Jim's CLEO Blog

Why a Temporal-Cloak is so Great: Uncovering the Hype

2012-01-26T13:14:00.000-08:00

(Figure from R. Boyd and Z. Shi, Jan. 5, "News and Views" Nature, explaining temporal-cloaking)

At Frontiers in Optics 2011 just this last October, Moti Fridman from Alex Gaeta's group presented work on a the first experimental demonstration of temporal-cloaking using a time-lens system. The work was based upon a theoretical paper from Martin McCall et al in the February issue of the Journal of Optics, and at the beginning of this month, appeared in an in-depth treatment in the January 5, issue of Nature. Besides the usual barrage of bloggers latching onto science-fictionesque results of new research, time-cloaking was also written up in traditional news media such as the Christian Science Monitor.

Temporal-cloaking certainly sounds like something out of Star Trek, but what is it and why is it so great? What makes a temporal cloak truly exciting, and what a majority of the recent articles and posts fail to highlight, is that the temporal-cloak allows cloaking over an infinite section of space albeit for a finite duration of time.

Let's imagine Harry Potter and his invisibility cloak. If the invisibility cloak is a temporal-cloak, Harry can move as far as he wants to the left-and-right and up-and-down without being seen for duration of the cloaking window. Harry can also move a little bit forward and backward without being seen, but not much or else he will walk out of the cloaking time-window (which is 50 ps for the Gaeta group's work or about 1.0 cm in fiber). It is crucial that he is in the right place in the axial dimension (forward/backward) since the window occurs at a specific place in space, but he has total freedom in the transverse dimension for the duration of the cloak. Conceivably Harry could pull-off a bank robbery as long as the bank and the vault are inside that particular infinite pancake of cloaking window and within the duration of the window.

Contrast that to a spatial cloak which gives cloaking for an infinite amount of time, but only a finite section of space. If Harry has a spatial invisibility cloak, then he can stand in one spot for as long as he wants without being seen.

Finally, if Harry has a spatio-temporal cloak, conceivably he can maintain invisibility for any duration of time and throughout any volume of space.

The temporal-cloak shown by the Gaeta group is not a practical cloak. If you scrutinize the setup you'll find that the way that they detect a cloaked event is through lack of nonlinear mixing. A nonlinear signal tells them the event is detected, and no signal tells them that the event is cloaked. You could just turn the power down to get the same result. They also couple into and out of the cloaking window with fiber-couplers between the cloaking apparatus. You can't send both the signal and the event to be cloaked down the same fiber because if the "event" goes through the same time-lens system as the "signal" the event will appear superposed instead of cloaked. Basically they had to sneak it into the right spot at the right time along a different path of propagation.

However, the point of the work was not to show practical temporal cloaking for masking or encryption, but to show the very odd, very fundamental, and very cool phenomena of creating and tailoring gaps in time. So even if the temporal-cloak won't be used anytime in the near future for cracking safes, it does bring the optics community closer to a true spatio-temporal invisibility cloak. It might be time to start brushing up on the rules of Quidditch.

Machining with Ultrafast Pulses

2011-12-12T07:30:00.000-08:00

(From Raydiance Inc)

As someone who has been trying to design novel ultrafast laser systems for the past eight years, my eyes were drawn to the title "Applications of Ultrafast Lasers" of Dr. Mike Mielke's talk from Raydiance, Inc. from the awesomely overwhelming list of invited speakers at CLEO 2012. Dr. Mielke's talk is one of a handful in CLEO's new Application and Technology conference which debuted last year in Baltimore in order to better bridge the gap between fundamental research and product commercialization.

To see what background information I could potentially find, I went to Raydiance's website to find a wealth of information on micromachining and a host of video shorts of ultrafast laser micromachining in action. They are so pleasing to watch, I couldn't help embedding many of them in this post.

Micromachinging with ultrafast lasers allows the removal of material without the introduction of heat (see the video above of laser micromachining on a match head without it igniting). Ultrafast lasers therefore give the advantages of laser machining- tailoring submicron features on the workpiece, without thermal collateral damage. For example, if you are going to have your dentist drill a tiny hole in one of your teeth (see the figure below) , you'd rather have her use the 350 fs laser shown in b) rather than 1.4 ns laser in a) in which the heat generated damages and fractures the tooth.

(Above: Drilling tooth enamel with a) 1.4 ns 30 J/cm²laser pulses and b) with 350 fs 3 J/cm²pulses. From B.C. Stuart et al LLNL.)

This is because drilling with the femtosecond pulses relies on an entirely different physical process for removal of material than nanosecond pulses. For long pulses (> 100 ps), photons are absorbed by the material and converted into heat. This eventually fractures, melts, or vaporizes material at (and nearby) the laser focus. On the other hand, if the pulse is fast enough (< 1 ps), the material is removed solely by photo-ionization. Rather than dumping energy into the material, electrons of target molecules are stripped off by the intense electric field of the pulse. No absorption takes place and therefore no heat is generated.

Because the mechanism for material removal using ultrafast pulses does not depend on the material properties as it does for thermal ablation, such as the melting point, conceivably any material can be machined using ultrafast pulses. This has allowed Raydiance to micromachine polymeric materials for manufacturing next-generation vascular stents and microfluidic devices (see the videos below).

(From Raydiance Inc)

Though micromachining using ultrafast lasers is not new, doing so in a robust workstation-platform is. Raydiance touts to have created the first "industrial grade" femtosecond laser platform. They have an impressive record and a current partnership with ROFIN GmbH for the development of industrial-grade femtosecond laser micromachining workstations. In the literature on their website they state, "A laser is not a solution. It might be the engine of a solution, however, 21st century manufacturing floors demand more: software integration, beam delivery, motion control, and visioning systems." As an "engine builder" myself it is helpful to know just what kind of engine is the most useful to workstation integration. Sometimes "engine builders" get caught up in making Formula One cars when what is most helpful is a reliable Hyundai sedan. Although not any pulse width, energy, and rep will do for athermal ablation, neither will a workstation without robust, continuous (thousands of hours 24/7), turn-key operation.

(From Raydiance Inc)

To that end, Raydiance's core platform, Smart Light, can simply be adapted (mainly turning down the power) for non-machining applications in defense and security such as remote sensing of hazardous chemicals and LADAR. Dr. Mielke's invited talk will likely emphasize Raydiance's pursuits in these areas since his talk is in the Government and Security subcategory. I will be interested to see what wavelength tuning options, wavelength conversion, or different center wavelengths Raydiance may be investigating for threat detection since Smart Light currently resides in the telecom C-band near 1550 nm and many absorption lines for molecules of interest live in the mid-IR. Until then, I hope you will enjoy, like me, these videos of lasers "vaporizing" material and leaving beautiful designs for very practical applications.

Using Soda Cans to Beat the Diffraction Limit

2011-10-19T21:12:00.000-07:00

(Above: Setup of the metalens (soda cans) used to focus a sound wave to a size of 1/25 th of the wavelength of the waves used to generate the beam)

Professor Mathias Fink from ESPCI ParisTech and Institut Langevin doesn't fit the typical profile for a plenary speaker at an optics conference, which is precisely why why you won't want to miss his plenary talk at CLEO 2012 this May. Though acoustics is the consistent medium for his work, his research more broadly consists of understanding the nature of waves and how to get around the limits assumed by our conventional understanding, such as diffraction-limited focusing and imaging. Much of professor Fink's work since the late 1990's has been using time-reversal, the subject of his upcoming plenary talk, to achieve these ends.

For example, in the August 5, 2011 issue of Physical Review Letters, Fink and collaborators demonstrated that they could focus a sound wave to 1/25 th of the wavelength of the waves used to create the focused beam. Ironically, this novel feat was obtained using very conventional objects- soda cans and computer speakers.

The MacGyveresque experiment shown in the figure above uses a grid of soda cans, a group of subwavelength acoustic resonators, to act as a "metalens". When illuminated with a broadband field, this metalens allows subwavelength detail in the near-field to be encoded onto propagating waves. Essentially the metalens is a very good evanescent-to-propagating-wave converter, "unsticking" evanescent waves with subwavelength detail that are typically locked to the surface of the object (or source) of interest. This phenomenon is analogous to the generation of surface plasmons in near-field microscopy (see the August 16th post below). The propagating waves, now containing subwavelength information, can be detected in the far-field and time-reversed (essentially run backwards) in order to focus to subwavelength spots.

Time-reversal essentially amounts to phase-conjugation. However, unlike optical phase conjugation, time-reversal is broadband. Rather, time-reversal is phase conjugation for every frequency at once.

In order to experimentally employ time-reversal, one needs a time-reversal mirror (TRM). For an acoustic wave, a TRM is essentially an array of piezoelectric transducers spread over a surface through which the wave of interest propagates. Each transducer records the wave at its unique position and then is made to play back the time-reversed copy such that the each wave retraces its complex path back to the source. Professor Fink and collaborators first demonstrated the power of time-reversal in the mid 1990's when they focused sound to a much smaller spot size than allowed by the aperture of the transducer array producing it. They discovered that when the source was allowed to scatter many times off of a random array of steel rods, they could reverse the signal such that it came back to a smaller spot size than the original source. The long path lengths from multiple scattering effectively widened the focusing aperture. When they removed the steel rods, they could only focus to the predicted size limited by the aperture of the transducer array.

In a 1997 physics today article, Fink explains time-reversal using an analogy of an exploding block:

"If we want to reconstruct an exploded block from the various scattered pieces, a time-reversal mirror would be a device that precisely reverses the velocity of each debris particle as it crosses a closed surface surrounding the initial block. But before being sent back, each particle must be held for an appropriate delay time: To reconstitute the block, one has to send back first the slowest pieces, which had arrived last."

Time-reversing an exploding block is of course thermodynamically impossible, however, for waves which can be described completely by a limited amount of information, it is reality. The strangeness of the multiple scattering experiment performed by Fink et al in the 1990's, and current experiments, is that it is as if the exploding block is being time-reversed to be put back together into a block that is smaller than the original.

So what about time-reversal for optics? Subdiffraction focusing and imaging in the optical domain have already been shown using a variety of techniques without time-reversal (for example, see Frank Kuo's September 10th post). However, two recent articles by McCabe et al, and Vellekoop et al show the optical analog of Fink's 1990's work, in which a highly scattering medium combined with time-reversal (via spatial light modulators) can be used to enhance an optical focus. Another recent work by Xu et al from Washington University shows a technique called Time-Reversed Ultrasonically Encoded (TRUE) focusing in which only the encoded portion of light from a microscope focal volume is time-reversed back to the sample for clean focusing. In this case the time-reversal mirror consists a holographic technique using a photorefractive crystal to a phase-conjugate of the right bit of light back to the focus.

I'm not only looking forward to Fink's plenary talk to learn about other uses of time-reversal in optics, but to generate ideas of what other wave phenomena may be borrowed from fields like acoustics, microwave communication, and quantum mechanics and visa-versa. After all, it's just the same wave equation.

Call for Papers

2011-10-02T22:53:00.000-07:00

October 1, marked the official call for papers for CLEO 2012 in San Jose, CA. I've decided to include a recurring gimmick in my past blog submissions for CLEO- a countdown clock. Mark your calendars for December 5, for submitting contributed work- there is still a good 63 days left to collect good data, put finishing touches on new instruments, or simulate new phenomena.

The official CLEO website has already posted plenary speakers. You can visit Expocad which will take you through the expo map, giving you booth information as you hover your mouse over different areas of the map. Stay tuned to this blog and CLEO's other various social media in the lower right-hand corner of the main page for the latest information for authors, attendees, speakers, students, and exhibitors.

Photonics for Global Health

2011-09-30T19:01:00.000-07:00

(Left: Reflection images of a histopathology slide corresponding to skin tissue using a low-cost, portable, lens-free off-axis holographic microscope. Right: Conventional reflection-mode microscope image of the same specimen using a 4X objective lens (NA: 0.1). Image from Biomedical Optics Express)

Research performed in the Ozcan group at UCLA holds a unique place in the field of optics and photonics. Besides the typical pursuit of advancing optical technology, another major initiative of this photonics group is solving problems of global world health, particularly in resource-poor countries.

Early September marked a milestone for the UCLA group as they published work on a compact, low-cost (~$100 USD of parts), dual-mode microscope with 2 micron resolution in Biomedical Optics Express (also written up in a recent OSA press release). The key to making such a low-footprint, low-cost, lab-grade device is using holographic microscopy. The image information stored in a hologram (the interference of the reflected or transmitted light from the specimen with a reference beam) requires no lenses, drastically reducing the weight, size, and overall expense of the device. A computer reconstructs the wavefront reflecting from (or transmitting through) the sample instead of a lens (see fig below). The impact to world health will be increased blood-diagnostics, water quality tests, tissue screening and analysis, and other imaging diagnostics in areas where microscopes currently are not available due to cost and/or remoteness of location. Getting more microscopes into the hands of health workers may have large impacts for heading off disease outbreaks as well as treatments for individuals.

(Schematic of the 200 gram microscope developed by the Ozcan group in reflection mode. LD: laser diode, PH: pin hole, BC: Beamsplitting Cube. Note the two AA batteries as the power source as well as for scale. Image from M. Lee, O. Yaglidere, and A. Ozcan, Biomedical Optics Express, 2, 2721 (2011). )

The idea of using holograms in microscopy is not new. In fact it was the quest for higher resolution in electron microscopy which prompted Dennis Gabor to devise wavefront reconstruction by holography in 1948. Gabor coined the word "hologram" which translates "whole message" to emphasize the amount of information that is stored in this very special interference pattern. For a brief history of holography from its roots in microscopy, its development through radar, and its boom in mainstream art and media in the 60's and 70's , see Jeff Hecht's 2010 OPN article.

What makes the Ozcan group's work so special is not the use of a fundamentally new technique, but clever and impressive engineering. This holographic microscope is small, inexpensive, and can work in both transmission and reflection mode. The transmission mode of the current device is similar to an earlier work by the Ozcan group- a cell-phone microscope. In the summer of 2010, the UCLA group published work in Lab on a Chip demonstrating a clever attachment to an ordinary cell-phone which could convert it into lab-grade microscope (see the youtube short below). By employing digital holographic microscopy, the group was able to produce a 38 gram attachment without any lenses, lasers, or bulky optics, which when incorporated with the cell phone camera, produced hologram on the cell phone detector array. The idea is that the hologram data would be sent over the same cell phone to the closest hospital/analysis station, a computer would process the hologram to extract the image information, and then the image would be sent back to the same phone, all within seconds of placing the sample to be analyzed into the device.

Though the current device cannot be so easily integrated onto a phone, the additional benefit of reflection-mode operation makes up for its "bulkiness." By operating in reflection-mode, the new microscope is additionally suited for imaging optically dense media like tissue, something not possible using in-line transmission holography due to spatial distortions in the reference wave. The developers decided to keep a transmission-mode an option, however, since it produces a larger field-of-view then its reflection counter-part and is easier to align and operate.

Once again a computer is needed to reconstruct the image from the hologram. However, hologram data could be sent to the nearest processing center if the field-worker is not carrying a laptop already. My thoughts immediately lead to the computer produced by Quanta through the One Laptop per Child initiative (OLPC). The XO laptop costs approximately $200 and can run on power sources such as solar, human power, generators, wind or water power. Though the aim of OLPC is to close the digital gap for children of resource-poor nations, I wonder if an XO equivalent could be developed to bridge the gap in digital medicine, not just on a records basis, but for data acquisition and processing for field-portable medical instruments like the microscope produced by the Ozcan group. I can imagine this $100 microscope interfaced with a $200 laptop.

What is exciting about this work is that it underscores the beauty and power of cross-discipline connections. Though lensless holographic microscopy is not new, using it as the foundation for a low-cost, field-portable devices is. To learn about more innovations like these, be sure to visit sessions this spring at CLEO Applications and Technology: Biomedical (just in its second year) in San Jose.

Year of the Plasmon

2011-08-16T13:20:00.000-07:00

(Left: August Cover of Nature Materials showing Liu et al s work on gas sensing using plasmonic response from a triangular nanoantenna. The work in the Nature article was expanded from that presented in CLEO 2011, postdeadline session)

This year may not be a flush for the market but it is looking good for plasmonics. Expansion of the the work shown in CLEO 2011, Postdeadline paper "Nanoantenna-enhanced gas sensing in a single tailored nanofocus," from Na Liu et al. just took the August cover of Nature Materials (see the figure above). Additionally, plasmonics has had a solid recent run of the main-stream physics circuit after the publication of two Physics Today articles earlier this year in February and July.

The July issue of Physics Today features an article by Lukas Novotny from University of Rochester in which he reviews near-field optics, the broader category where plasmonics resides. Earlier in the year, Mark Stockman of Georgia State University wrote a very accessible and informative article on nanoplasmonics that took the cover of the February issue of Physics Today. The cover shows a 13th century stained glass window of Sainte Chappelle in Paris whose yellow and red brilliance are assumed to come from nanoplasmonic resonances of silver and gold nanoparticles in the glass. The optical effect of how the red changes over the length of the window is said to have purposely been designed to mimic the flowing blood of Christ.

(Above: Sketch of Edward Synge's proposed near-field microscope. The red dot denotes the gold nanoparticle. Picture from L. Novotny, Phys. Today, 64, 47 (2011))

Novotny's July article also offers a romantic insight into the history of near-field optics and plasmonics. Novotny, recounts how in 1928, Edward Synge wrote a "prophetic letter" to Einstein proposing a near-field microscope (see Figure above) to optically image a biological sample below the diffraction limit. Synge's proposed microscope, which could not be realized until 1982 (by Dieter Phol's group at IBM of Switzerland), looks eerily familiar to current techniques used for the development of plasmonic devices and sensing- the use of metallic nanoparticles to generate surface plasmons in order to enhance a probing optical field. The two Physics Today articles are must-reads for those who need a crash-course on plasmonics.

A plasmon is created when the electrons on a metal surface are periodically displaced with respect to the lattice ions by an external, driving, optical field, creating an "electron oscillator." The frequency of the surface plasmon depends not on the driving field, but instead upon the restoring force and effective mass of the electrons in the metal. Changing the size and geometry of the metal structure will alter the restoring force and thereby the plasmon frequency. Using metallic nanostructures of the right size (smaller than the skin depth of the metal but bigger than the distance an electron moves during on optical cycle, 2-20 nm) the electric field due to the plasmon becomes highly localized in the immediate vicinity of the outer surface of the nanostructure (see the Figure below). By coupling the surface plasmon to propagating optical radiation, nanoscale information from the plasmon can be encoded micron-sized optical waves as it is in near-field microscopy. The highly localized field can also be used for a number of sensing techniques like SERS by which the interaction of a probe beam with a molecule is significantly enhanced due to the presence of nearby nanostructures. The cover article from Nature Materials uses a standard plasmonics approach by using redshifted plasmon response itself from a gold triangle structure for ultra-sensitive detection of hydrogen.

(Above: Diagram of plasmon dynamics on a 10 nm silver nanosphere. Eo represents the external light field, the black arrows represent the electric field from displaced electrons, the plasmon field, and the red arrows show the field inside the sphere. Picture from M. Stockman, Phys. Today, 64, 39 (2011) )

The exciting field of plasmonics has applications and positive repercussions in other fields as well. Tumor cells have been found to readily take up nanoparticles. By illuminating tissues with non-lethal IR light, the heat generated from enhanced local-fields of the high-Q nanostructures selectively kills cancer cells. Plasmon-enhanced solar energy conversion entails using metallic structures to better localize light for solar concentration. The opening tutorial, "Solar Energy Applications of Plasmonics," by Professor Harry Atwater of Caltech in CLEO:QELS session "Frontier Applications of Plasmoincs" during CLEO 2011, addressed this burgeoning new field.

There is no doubt that CLEO 2012 will host a number of technical and invited talks, both fundamental and applied, on the subject of plasmonics. After reading the Physics Today articles, I think I will have to add a lecture or two on plasmonics in my junior-level E&M class this fall. I will definitely have to attend some plasmonic talks next CLEO to learn more about this extremely interesting work that saddles fundamental physics and cutting-edge applications.

Are we Entering a Solar Boom?

2011-07-12T19:38:00.000-07:00

(First Solar employees working on the 21 MW solar power station in Blythe, CA in the Mojave Desert. The project was completed in December 2009. Photo from cnet News; originally from First Solar. First Solar just received $4.5 billion in DOE loans to build three new stations in the Mojave Desert whose total output will be 1.33 GW)

This summer seems to be marked by a frenzy of solar energy initiatives and development. The Business News section in the May issue of Nature Photonics reported on four recent major investments in solar technology manufacturing: JA Solar of Shanghai plans to build a 3 GW capacity plant in Hefei, China for the manufacturing of monocrystalline silicon solar cells. Investors have pledged $2.05 billion over the next four years, and production is slated to begin in 2012. Polysilicon Technology Company, a joint venture between Mutajadedah Energy of Saudi Arabia, and KCC Corporation of Seoul will build a $1.5 billion facility to produce solar-grade polysilicon in Jubail, Saudi Arabia by 2017. The Indian government is discussing a joint venture with nanotech company, Rusanano, of Moscow to obtain a consistent supply of silicon for Indian photovoltaic manufacturers with hopes of obtaining 2,000 tons of silicon ingots for solar cell production. And SoloPower of San Jose was guaranteed $197 million from the U.S. Department of Energy (DOE) to build a plant in Oregon for the manufacturing of flexible copper-indium-gallium diselenide (CIGS) for light-weight solar panels.

Though CIGS are not as efficient as crystalline silicon, like other thin-film technologies they reap benefits of inexpensive fabrication and production when compared to silicon cells. CIGS need only a fraction of the material to absorb incident photons. They can be manufactured in large-area, automated processes unlike more time-intensive and expensive ingot growth used for silicon. The flexible thin-film technology allows SoloPower's CIGS panels to be 75% lighter than traditional panels for less expensive and more practical installation on industrial roof-tops.

The DOE made even bigger news for solar energy investment, however, at the end of June when it promised $4.5 billion for the construction of three different California photovoltaic power plants: Antelope Valley Solar Ranch 1, the Desert Sunlight Project, and the Topaz Solar Project. Arizona-based company First Solar, Inc will sponsor all three projects, constructing each solar array with cadmium telluride (CdTe), thin-film photovoltaic modules. Together, the new power plants will provide 1.33 GW (powering the equivalent 275,000 U.S. homes) and offset the generation of 1.8 megatons of carbon dioxide. As described by Alexis Madrigal, author of "Powering the Dream: The History and Promise of Green Technology," (Da Capo Press, 2011), in a June 17, interview on NPR's Science Friday, the Mojave Desert solar plants will prove to be particularly effective when compared to other green initiatives. One reason for their effectiveness is their location- the solar plants will be simultaneously near large population centers, L.A. and Las Vegas, with ideal conditions for sunshine- the desert. This is in contrast to wind energy where ideal locations for wind farms often correspond to areas with low population densities (like the plains of North Dakota) and so power distribution becomes an issue. Additionally, the sunlight in the desert suits itself to matching peak output of the solar grid with peak usage- as everyone cranks up the air conditioning at the hottest time of the day, the PV modules are cranking out the most amps.

(Time-line of photovoltaic efficiencies for various cell types; from the National Renewable Energy Lab)

The choice of thin-film CdTe for the solar cells is once again due to balancing cost and efficiency. First Solar claims that its CdTe modules have the smallest carbon footprint (this includes fabrication and recycling of the module over its lifetime) compared to any photovoltaic on the market, as well as the fastest energy payback time (EPBT). They also note that the high temperature coefficient of CdTe allows their modules to perform better than silicon at higher temperatures, which will obviously be crucial given the heat conditions of the Mojave.

Other summer solar news include McGraw-Hill's June 13, announcement to build the world's largest private solar plant at its East Windsor, New Jersey campus. Though New Jersey is not as sunny as the Mojave Desert, the plant is slated to generate an impressive14 MW.

A detailed solar map was released by the City University of New York on June 16, which shows the solar energy production potential of the New York City's rooftops. The New York Times reported that the solar map, made by making LIDAR sweeps the previous year, shows that two-thirds of New York's rooftops have great potential for solar harvesting. If these rooftops were covered with solar panels, the city could use them to meet half of its electrical power consumption needs, even at peak use.

NYC roofs were not the only ones in the solar lime-light recently. Google announced on June 14, a partnership with SolarCity in which they will provide a $280 million fund to help finance SolarCity's solar panel leasing program for rooftops across the U.S. The largest hurdle for residential solar panels is the up-front cost and installation of panels, typically tens of thousands of dollars. By bankrolling SolarCity's leasing program, Google will put solar panels on the roofs of more U.S. homes. Other U.S. companies with solar leasing programs include Sungevity and SunRun.

In more solar news, IEEE released a statement on June 15, projecting that solar power could become the most economical form of energy generation in the next 10 years, provided a continued increase in efficiency of photovoltaics and development in mass production of of solar cells.

To that aim, a collaboration between Japan’s New Energy and Industrial Technology Development Organization (NEDO) and the European Commission, which began June 1, 2011 will attempt to push PV efficiency to greater than 45% in the next four years. The record is currently just over 40% in concentrator, multi-junction devices made by companies like Sharp, Spectrolabs, Spire and Solar Junction (see efficiency curve above). To meet this goal, the Japanese-EU collaboration led by Antonio Luque of University of Madrid and Masafumi Yamaguchi of Toyota Technological Institute will pursue an approach using multi-junction cells, but will also explore options of adding nanostructures like quantum wells or quantum dots. They will also try to enhance the design of typical solar module concentrator optics.

The potential solar boom will not only be good for our planet but will provide the optics community with new challenges and opportunities in R&D. If investment in solar energy continues at its current pace, we could see a significant shift in the funding and direction of optics research. Whatever the shape or face of the next best efficient or cost-effective solar cell, be rest assured you will hear about it at CLEO.

Capitol Hill Day

2011-05-11T21:38:00.000-07:00

(From Left: Laura Kolton (OSA Public Policy Team), Greg Quarles (President of B.E. Meyers Electro Optics), James van Howe (Assistant Professor, Augustana College), Representative Bobby Schilling (IL), Adam Zysk (research associate IIT, Chicago), Hong-Jhang Syu (Research Assistant, National Taiwan University))

On Thursday May 5th, a number of the conference attendees took a bus to Washington D.C. to visit the offices of various members of congress and senators of our respective legislative districts and states. Our goal was to help defend science funding levels in the wake of strong national sentiment to reduce U.S. federal spending.

What we learned the night before in the briefing at the Baltimore Convention Center was fascinating, and the actual day of visiting policy-makers to discuss science-funding issues was exhilarating. In the briefing, we learned that one of most effective ways of influencing a senator or member of congress was through a conversation with a constituent. Visits from lobbyists actually rank much lower on survey data from congressional staffers. What was also fascinating to me was that an email from a constituent ranked just below a visit from a constituent and still far above a visit from a lobbyist. I immediately promised myself to regularly send email to my representatives and you should too! It works!

At the briefing, one of the speakers, Mike Lubell, the Public Affairs Director at the American Physical Society, showed us revealing survey data from focus groups. One group was from a community with many ties to science industry and one had very little. Shockingly, the results were the roughly the same for each:

1. The groups generally loved science and are supportive of science research
2. The groups thought that science should be a national priority
3. Here's the kicker: The the groups were distrusting of the federal government as the funding source for science research. Somehow they want to keep good science without federal funding.

So there is good and bad news. Scientist can expect good moral and emotional support from the public, but maybe not dollars. In fact, Lubell showed a list that had science as the second most chosen category from the groups of where to cut federal funding.

Our task for the Capitol Hill visits was well laid out- try to educate our representatives about the role of federal money in science research; how it is almost the sole source for science funding in the U.S., how science requires sustained funding over time for results, and how our quality of life is enhanced by the technology we develop such as noninvasive biomedical imaging techniques for cancer diagnostics and photovoltaics for green energy production, not to mention the highly skilled workforce good science creates.

I particularly liked Lubell's list of "good" and "bad" words and phrases to bring up or avoid as you are trying to convince non-scientists of the importance of federal funding for science. Words like "basic research" and "fundamental research" did note bode well in the public eye. They took "basic" and "fundamental" to mean "remedial." The phrase, "Investing in America's future," tracks well with Democrats, but not Republicans since "investment" to the GOP means "spending." There was a fairly strong equal distaste among different parties for the idea that America needs to be the top competitor among foreign nations in science. I guess our Cold War attitude as been slipping since Reagan administration. A "good" party-neutral phrase is the cheesy (sorry but it is), "Building a better America." The list goes on and is both entertaining and illuminating as to the perception of science in the U.S.

Because I live in Iowa but work in Illinois, I met a handful of staffers from both states. From the picture above, you can see that my team was able to personally meet congressman Bobby Schilling (R) from Illinois. Congressman Schilling was extremely kind and hospitable, as were the staffers from the other offices we visited: Senator Kirk (R-IL), Senator Grassley (R-IA), Congressman Quigley (D-IL), and Congressman Braley (D-IA). I was very impressed with the professionalism and cordiality of the young staffers who took the time to listen to our concerns.

So I know you are now asking yourself, "What can I do to help?" Begin by emailing your representatives with your concerns for science funding (at the Capitol Hill visits we were advocating sustained levels (not an increase) . Also be sure to visit the OSA public policy homepage for updates on additional organized Capitol Hill visits, pending science-bearing legislation, letters to sign, etc.

For more info and photos on the Capitol Hill day event click here.

See you in San Jose!

2011-05-08T22:35:00.000-07:00

I hope this post greets everyone safe and cozy at home, resting from a week packed of optics innovation. I am still catching my breath. There was just so much. I would have liked to have attended many more talks, visited more booths at the expo, met up with more colleagues, and posted more (I still might on the latter- it turns out, for better or worse, Newton's First Law applies to blogs as well). Harold Metcalf was correct is is pre-CLEO analysis "Looking over the program and the titles of the sessions, I feel like a kid in a candy store- with unlimited funds, but limited time. It's impossible to do everything."

However, I intend to update this ClEO blog for a little longer with posts that I couldn't squeeze in during the week. I am going to try to have my "candy" and eat it too, though hopefully without a stomachache (figuratively or literally) for blogger or reader.

Regardless, mark your calendars for May 6-11, in 2012 for next year's meeting in San Jose!

Time-Lens 2.0

2011-05-07T19:16:00.000-07:00

Brian Kolner and Moshe Nazarathy coined the word "time-lens" in 1989 after using one to compress a pulse. They made a system in the time-domain that was a complete analog to a lens system in space. Their time-lens took a fat pulse and "focused" it, just like a spatial lens could take a fat beam and focus it to a smaller size. For more details, see Kolner's well-written 1994 review on space-time duality and van Howe and Xu's 2006 review on temporal-imaging devices).

Because much of my thesis work focused (pun intended) on temporal-imaging devices, I can't help seeing them everywhere. This year's CLEO conference was no exception with some talks being more direct about it than others.

Takahide Sakamoto from the National Institute of Information and Communication, in Tokoyo, Japan discussed time-lenses without using the word itself in tutorial, CMBB1, in "Optical Comb and Pulse Generation from CW Light." Sakamoto showed impressive work on comb synthesis from CW light using electro-optic (EO) modulation. He demonstrated that EO phase modulation provides the most efficient way to move from CW light to the picosecond bandwidth regime. Higher order nonlinearities like chi-3 from fiber (EO is chi-2 process) can then be used to move bandwidth to femtosecond regime. Sakamoto stressed a clever biasing and driving technique using an itensity modulator that allowed truly flat comb spectra.

Other work leveraging temporal imaging concepts were CMD1, "Tunable high-energy soliton pulse generation from a large-mode-area fiber pumped by a picosecond time-lens source," from Chris Xu's group at Cornell University and JTuI77, "Scalable 1.28-Tb/s Transmultiplexer Using a Time Lens" by Petrillo and Foster. The former used electro-optic modulation as the time-lens to generate a seed source from CW light for solition shifting. The latter used four-wave mixing as the time-lens mechanism in order to look at the Fourier transform of a data packet for high-speed time-division multiplexing to wavelength-division multiplexing conversion (just as a spatial lens can provide a Fourier transform of a spatial profile, a time-lens can give the power spectrum of a temporal profile). Note that the Xu group has also developed time-lens source for CARS microscopy.

Work from Andrew Weiner's group also made use of time-lenes, CWN3, "Broadband, Spectrally Flat Frequency Combs and Short Pulse Sources from Phase modulated CW: Bandwidth Scaling and Flatness Enhancement using Cascaded FWM" and CFG6, "Microwave Photonic Filters with > 65-dB Sidelobe Suppression Using Directly Generated Broadband, Quasi–Gaussian Shaped Optical Frequency Combs." These works used a front end similar to those shown by Sakamoto, but then added an assisted nonlinear enhancement to bandwidth by using four-wave mixing.

Finally, former CLEO Blogger, Kesnia Dolgaleva, authored CThHH6, "Integrated Temporal Fourier Transformer Based on Chirped Bragg Grating Waveguides" to show a compact, integrated Fourier Transformer, which though not a time-lens, is another device similarly based on space-time duality. This paper draws upon co-author Jose Azana's previous fiber Bragg grating work, which is just one of many Azana's contributions to the field of temporal imaging.

If you look hard enough, you can see time-lenses anywhere- all you need is a device that gives a quadratic phase in time to an optical wavefront (nonlinear frequency mixing, used everywhere in optics, is one technique that works well). However, the big advantage for recognizing a time-lens when you have one is that you can bring all of the knowledge of spatial imaging systems to your work with a simple change of variables.

The Real-Life Tony Stark

2011-05-05T20:41:00.001-07:00

(Robert Downey Jr. plays Tony Stark, defense contractor, billionaire playboy, scientific genius, and alter ego Iron Man. Image from www.comicbookmovie.com, still from Iron Man 2)

On Tuesday, May 3, I sat in on part of the Market Focus talks at the CLEO expo on defense. The Market Focus sessions cover various business and commercial applications of optics research. Last year was the first time I attended a Market Focus session, and I knew I had to go back. It is a little expo in itself that requires no walking- you to sit down and find out trends and problems that need solving in particular commercial areas. Great fodder for new research ideas!

Although the sessions are broken up into specific talks, what makes these sessions unique is that they turn into a round-table discussion at the end (and even during) the session. They have a more intimate and informal feel than the technical talks and have been organized with a specific agenda of bringing the attendee to a common understanding of the particular market being addressed.

For example, in the defense session, moderator John Koroshetz from Northrop Gruman Laser Systems laid out the logical order of talks to help us get our foot in the door of defense contracting: 1) Science and Technology Development, 2) Product Development, 3) Manufacturing, and 4) The Soldier's perspective. The aim was to help a novice understand the cycle of product development, funding, testing, manufacturing, and end-use, which often cycles back to development for upgrading and enhancing the product into its next-generation phase.

The first speaker, Craig Hoffman, from the Naval Research Laboratory, described science and technology development of infrared imaging systems. He broke up NRLs work in this area by spectral region:

-Visible: 0.4-0.7 microns (high photon energy makes devices tolerant to noise, but scattering makes it bad for imaging through dust or fog)

-Near IR: 0.7-3.0 microns (better for imaging through climate, but resolution gets worse because the wavelength is getting longer; becoming less tolerant to noise)

-Mid-IR: 3.0-5.0 microns (getting very good at seeing through climate, but getting even worse with resolution and noise tolerance; detectors may need to be cryogenically cooled to circumvent thermal noise)

-Longwave: 5.0-14.0 microns (least prone to scattering, worst for resolution and noise)

NRL is looking to piggy back imaging systems in these regions for applications in target acquisition, surveillance, and reconnaissance. The shorter wavelength systems use reflected light to gain information about detail of a target whereas the longer wavelength systems make use of emissive properties of a target to gain bulk properties like thermal imaging.

For example, new thermal imaging systems use mid-infrared light detection to gain detailed information about a target, but also use longwave detection in order to gain a wider field of view. You need both since by themselves the former sacrifices field for resolution and the latter sacrifices resolution for field.

Hoffman went on to describe military imaging problems that need better answers 1) Detailed target identification. You don't want to just know if a target is a tractor or a tank, but exactly whose tank it is (friend or foe?) and with enough time to either make evasive maneuvers or decide how to engage. 2) Fast data acquisition for reconnaissance. For this application, you want to collect data from an aircraft that is flying high and fast. You don't have the burden of real-time analysis like target acquisition (you can spend weeks later to analyze data), but you do need to collect enough information, with enough quality during the short acquisition time. 3) Surveilling a small area for weeks on end to look at changes in patterns like traffic flow, building construction, etc.

Hoffman spoke briefly about things like SWaP- size, weight, and power. This acronym represents all the things that should be as small as possible for a viable military product. Pete Vallianos from N2 Imaging systems followed up Hoffman's talk with more of the parameters, tests, and requirements related to SWaP. Vallianos underscored the importance of practicality and robust requirements when it comes to making products for the military. He repeatedly reminded the attendees that the military is not interested in your research per se (definitely not technology for its own sake), but rather interested in how technology might solve problems. While being developed, it needs to go through a variety of rigorous tests- one of the stress tests from the Marines is dropping your product from a height of six feet onto a piece of plywood . If it doesn't survive, it's back to the drawing board.

Vallianos described some specific product development interests of the military in imaging:

-microbolometers
-small eye safe lasers
-CMOS, low level light detection
-lightweight visible optics
-high transmission in optics across the visible spectrum through the longwave IR
-moldable aspheric lenses
-robust broadband optical coatings
-OLEDs
-LCDs
-Lightweight optical "network" on a soldiers back
-Any decrease in power for powered optics to get grid of as many of the batteries as possible a soldier needs to carry in his or her pack.

Though the speakers did not describe any iron suits with flying capability, or magic cold-fusion-like power supplies, I think Tony Stark still would have been proud of this session.

Post-deadline Prep

2011-05-05T14:29:00.000-07:00

Just wanted to chime in with a nagging note to remind you to plan your post-deadline itinerary before 8 pm. I am going to commit to PDPA-Session I and not try to hop around the standing-room only crowd. I am particularly interested in the supercontinuum generation and frequency-comb work in this session, some of which is pushing into the mid-ir where there are interesting chemicals to identify for spectroscopy and stand-off detection. Other broadband generation in this session has been performed with small waveguides or micro-resonantors- little pocket combs on silicon (see the April 20, post for more details). I will be disappointed to miss the new Applications and Technology Session, particularly the biomedical work. These groups by far always have the coolest pictures, images, and videos. If you can make it to these talks, the first four of PDPB-Session II, be prepared to be blown away by beautiful videos and images that address improving image acquisition rate, penetration depth, and resolution (again, see the April 20, post for more details). Very likely, these state-of-the-art techniques may be used on you in your lifetime. You can tell your doctor, "I saw this work at CLEO 2011 before you even graduated from med school."

The Romance of Photonic Lattices and Ham

2011-05-04T20:51:00.000-07:00

(Left: beam profile in one of Mordechai Segev's 2D photonic crystal lattices. The transverse disorder increases from c) to e). From Schwartz, Segev et al)

This year's CLEO plenary sessions were exceptional. Monday evening hosted talks by Donald Keck, who pioneered the first low-loss optical fiber and James Fujimoto, renown for developing optical coherence tomography. Wednesday morning's plenary followed with exhilarating work (I'm serious, not just blogger hyperbole here) on photonic crystals. Even the awards were exciting. Amnon Yariv, responsible for the creation of the distributed feedback laser, and whose book "Optical Electronics in Modern Communication," I safeguard as one of the most helpful optics texts on my shelf, was presented with the 2011 IEEE Photonics Award. In his acceptance speech, he spoke briefly of his emigration to the United States from Israel 60 years ago. The freighter that carried him, other passengers, and iron ore across the Atlantic, made entry in none other than the city of Baltimore. Yariv, reminisced about his first meal after landing in a gritty, industrial, 1950s Baltimore-a ham sandwich (his first ever)!

After the awards, the plenary speakers Mordechai (Moti) Segev and Susumu Noda spoke about their respective work on photonic crystals. Segev, a charismatic speaker, setup a beautiful story addressing a fundamental understanding of periodic and random structures via photonic lattices. He specifically spoke about work on Anderson Localization of Photons, the optical analog to Anderson's Theory for Localization of electron's in a crystal lattice. By introducing disorder into a 2D photonic lattice, Segev was able to constructively interfere light over a small area, and destructively interfere light everywhere else. Diffraction is thwarted, analogous to how diffusion is thwarted by the interference of electron waves for Anderson Localization in a crystal lattice (see figure above). Check out Frank Kuo's February 26, blogpost with more details describing this work.

Segev's group of course has pushed this work further, and into stranger directions. In contrast to confinement, Segev's group found that they could make a beam expand faster than diffraction, hyper-transport. One reason this work is so beautiful is that the theory and phenomena for photonic lattices can be borrowed from crystal lattices in condensed matter and visa-versa. The equations are the same, you just need to change the variables and some good creativity. In 2008, Roati et al leveraged work from Anderson Localization in photonic lattices to demonstrate Anderson Localization for the first time using matter waves. This makes me wonder about a designing a crystal structure with say hyper-diffusion? With a sharp mind and good imagination, the possibilities seem endless.

Segev does a fantastic job framing his work romantically. Though the devices his group makes have great practical implications, it is all through the guise of exploring the nature of world. Segev helps remind us why we became interested in science in the first place, for the thrill of exploration and finding answers, to generate new questions, and to pursue things because they are beautiful.

Segev was a tough act to follow, but Noda came through. After Segev's nice setup, Noda showed one impressive photonic crystal device after the other. Here is a list of some of the groundbreaking devices he has made:

-Nano-cavities with Q > 40,000
-Inhibition of spontaneous emission
-Light that can make right angle turns
-Slowing or stopping light with probe pulses
-Novel gates for quantum computing
-Small beam-steering devices
-High-efficiency, high power single wavelength emitters
-Creation of unique beam patterns for applications like optical trapping of non-dielectric particles
-Sub-wavelength focusing of beams
-Thermal emission control (shaping and redistribution of blackbody spectra)

Again, for details on the physics behind some of these devices, see Frank Kuo's February 26, blogpost. I left this plenary session inspired, ready to get into the lab to get some work done, and strangely with the craving for a Baltimore ham sandwich.

Lasers can Mold and Manipulate Metal as easy as Play-doh

2011-05-03T13:01:00.000-07:00

(Left: Dr. Marshall Jones from GE Global Research; Photo from GE)

The head of the student machine shop at Cornell, Bob Snedeker ( Sned), liked to remind us in a sarcastic fashion that its easier to take material away from a workpiece than to put it back on- warning: be careful about how much you take off as you cut. Or as the old saying goes in carpentry, "measure twice, cut once." This is not necessarily true for laser machining of metals. Laser cladding, which was one of the topics discussed in the tutorial, AMB1 "Industrial Applications of Laser Materials Processing," by Dr. Marshall Jones from GE Global Research, is a technique in which material can be added to a workpiece where too much was accidentally cut off. Like Play-doh, you can just put back on what you need. Wow, if only I could have laser-cladded my tool bits, and special nut and bolt we were required to make in order to graduate from machine-shop training! Sned had high standards and we spent many hours to make a piece to find out we needed to start over with fresh stock. It was back to the grindstone (literally!) until those bits had a perfect angle and facet.

GE uses laser cladding to clean up mistakes that may have been made for particularly expensive pieces such as airfoils for aviation. You don't want to throw these out and start over. Laser cladding is also used for coat metals with another protective metal surface- hardfacing.

Another laser processing technique explained by Marshall was laser-shock peening. Peening (as in a ball peen hammer-a remnant tool from days of blacksmithing) is a technique that reduces the fatigue of a metal (like preventing cracks from spreading) by applying a compression force to the surface. In the old days, this was done with a hammer, Marshall uses a "laser hammer." To create a shock wave powerful enough to peen, you need a laser beam with an a power density of 10¹⁰ W/cm² and an interaction time with the surface of no more than 10 ns. Using an interface like water, through which the compression force propagates to reach the metal surface, can make peening more effective. GE also uses shock peening for aviation pieces in order to extend the life of a particular part.

Marshall also discussed a handful of additional applications for laser welding at GE. GE rail uses laser welding for their diesel engine heads and liners. Their consumer division uses it to weld electrodes of ceramic metal halide lamps- the ones that give a nice white-light spectrum crucial for lighting for retail. Marshall brought up the fact that jewelers and clothing retailers particularly need white-light illumination in their stores to ensure customer satisfaction (you don't want what you thought was a red dress to turn out to really be magenta when you leave a shop and get out into the sunlight). The ceramic metal hallide lamp electrodes are particularly tricky to weld together because of the need to join odd materials W:Mo welds and Mo:Nb welds. GE uses a special three-beam laser system to join these materials.

Finally, Marshall briefly discussed the laser systems themselves used for such applications. The conventional lasers used for processing are CO2 lasers and Nd:YAG systems that give out approximately 20 kW average power. Unfortunately they have 10% and 3% wall-power efficiency respectively, and CO2 lasers require expensive specialty fiber for coupling due to the long emission wavelength. Ytterbium-doped fiber lasers and ampliers are beginning to replace these current workhorses due to high wall-power efficiency, 30%, and all-fiber configurations (zero optical alignment and high flexibility in footprint and beam delivery). The main disadvantage to high-power fiber lasers is expense. However, as fiber-systems continue to be developed, they may very well replace their bulk system competitors in the near-future.

Small, Mountain-Town Mecca for Optics Research

2011-05-02T18:40:00.000-07:00

(Above: Big Sky Laser series compact Q-Switched, Nd:YAG from Quantel Laser. Author's note: may not be best to combine beautiful Montana stream with Nd:YAG)

I am likely showing my naivete as a "young" optics researcher, but after my Super Shuttle ride from the airport to my hotel last night, I felt compelled to say something about Bozeman, Montana. And no, I'm not being paid by Bozeman's Chamber of Commerce (though if you are paying attention Bozeman, an all-expenses-paid visit to Bozeman could convince me to write more about your town whose combination of optics innovation and gorgeous backdrop is causing me to want to pack up my bags and head out West to Big Sky Country.)

What peaked my interest about Bozeman were two passengers in my Blue Van who were employed by Bozeman optics companies. I knew ILX Lightwave was out of Bozeman, but didn't realize that was just the beginning. One of the passengers was an HR rep from Quantel. Note to job seekers: Quantel-Medical, which makes laser systems for ophthamology and dermatology, is looking to fill several positions. Find out more information at the CLEO Job Fair.

My surface internet searching led me to make a stab at a list of photonics companies in Bozeman (a booth number adjacent lets you know that they will be at the expo which opens at 9:45 am tomorrow):

AdvR (booth 1330)
Altos Photonics (booth 1225)
Bridger Photonics
ILX Lightwave (booth 1808)
Lattice Materials
Resonon
S2
Scientific Materials Corp
Quantel (booth 1903)
Quantum Composers

This list, which is by no means complete, is still very impressive given that the population of Bozeman is just under 40 thousand.

So why all the optics in Bozeman? A 2005 article from the Bozeman Daily Chronicle gives credit to Montana State University professors Pat Callis and Rufus Cone for strengthening the optics program in the late 1980's which led the establishment of a handful of companies in 1990, such as ILX Lightwave, Big Sky Laser (now Quantel), and Lattice Materials. To further the growth of optics at MSU and colloboration between industry, OpTec was created in 1995 as a multidisciplinary center for optics research. In 1999, Spectrum Lab was formed to specifically transition photonics research from MSU to Montana companies. Bozeman companies have also been no strangers to Small Business Innovation Research (SBIR) grants to bolster the development of optics start-ups.

Be sure to stop by the Bozeman contingent at the expo, if not to talk optics and photonics, at least to hear adventures of fly-fishing, downhill skiing, rugged hiking, and glacier climbing!

Photonic Spark Plugs: Zero to Ten Millijoules in just a Nanosecond

2011-04-25T14:00:00.000-07:00

(Prototype of a photonic spark plug using Q-switched Nd:YAG/Cr⁴⁺:YAG microlasers (top), and a standard automobile spark plug (bottom). Photo from Takunori Taira, National Institutes of Natural Sciences, Japan)

An April 20, CLEO press release recently caught the eye of the BBC News, and with good reason. A Japanes and Romanian collaboration will show data at CLEO from a 10 mm, multi-beam, ceramic laser whose beams can reach energies greater than 10 millijoules over a 800 picosecond pulse width, to ignite fuel for internal combustion.

The research behind the photonic spark plug will be presented in, CMP1 “Composite All-Ceramics, Passively Q-switched Nd:YAG/Cr4+:YAG Monolithic Micro-Laser with Two-Beam Output for Multi-Point Ignition” on May 2, at 1:30 pm, by Takunuroi Taira and Matsaki Tsunekane from the Laser Research Center in Okazaki, Japan, in collaboration with Kenji Kanehara from Nippon Soken, Inc. in Japan, andNicolaie Pavel of Romania’s National Institute for Laser, Plasma and Radiation Physics in Romania.

There are a handful of advantages to using photonic spark plugs over conventional spark plugs. A photonic spark plug could potentially ignite leaner fuel mixtures (more air and less fuel) to reduce emissions of polluting nitrogen oxides (NOx). Conventional spark plugs cannot practically accomplish this right now because the increased spark-voltage required to ignite lean mixtures erodes the electrodes too quickly-they need to be replaced too frequently which is expensive.

Additionally, a photonic spark plug could improve combustion efficiency for better driving performance and/or fuel economy. A conventional spark plug sits on top of the head of a cylinder and ignites the fuel mixture near the top where there is a large thermal mass of cold metal from the cylinder. Taira's photonic spark plug can focus the beams into the center of the gas mixture for three times faster, and a more symmetric, expansion of the flame. Also, the ignition time-scale using the pulsed micro-laser beams is nanoseconds compared to milliseconds for a conventional spark plug. The ability to better control ignition timing over an automobile's cylinders will result in more power delivered to the drive-train when desired.

The Japanese and Romanian collaboration is already working with DENSO Corporation, an affiliate of Toyota. Keep your eyes out for photonic, fiber-patch cord jumper cables in the near future!

Postdeadline Papers show Emphasis in Broadband Light Generation, Biomedical Imaging, and Nanophotonics

2011-04-20T13:10:00.000-07:00

(Fig. 1 From P. Del'Haye, Nature, 450 1214, (2007). a) frequency comb spectrum, b) degenerate and non-degenerate four-wave-mixing among cavity modes, c) SEM image of torroidal microcavity)

On Thursday May 5, from 8pm- 10pm, conference goers will be madly dashing from ballroom to ballroom to hear the latest breaking optics research- it's like a geeky Black Friday for optical science. There are 36 talks in total, but because they are spread out among three sessions, you realistically can only hear 12. Trying to see more requires cat-like agility to maneuver around standing-room-only crowds. Good thing postdeadline abstracts were recently posted. Be sure to look through the agenda of sessions and plan your evening.

This year's sessions include record breaking feats typical of CLEO postdealine papers: an ultralow 181 nA lasing threshold in a nanocavity laser (PDPA1), a whopping 4176% W^-1cm^-2 conversion efficiency for parametric fluorescence in a diode laser (PDPA3), a limit-pushing 1.5 mm imaging depth in a mouse brain cortex using a two-photon microscope (PDPB3), Mid-IR to keV X-ray supercontinuum generation (PDPC12), a noise figure less than 3 dB in a phase sensitive amplifier (PDPB10), and many others.

Though the sessions will host a wide variety of topics in fundamental and applied optics, some themes that emerge from this year's postdeadline abstracts are papers that demonstrate broadband frequency generation, biomedical imaging (the postdeadline subcategory CLEO: Applications & Technology 1: Biomedical has the most papers of the three sessions), and nanoscale lasers and nano-photonic devices.

One of the papers on broadband frequency generation, PDPA4, "Mid-Infrared Frequency Combs Based on Microresonators," by Wang et al. from a German, Swiss, and French collaboration (note one of et al's s is Nobel Laureate Theodor Hansch), builds on previous work reported in a 2007 Nature paper to produce a monolithic comb generator in the Mid-IR. The reason for the microresonator is to get rid of the big Ti:Sapphire laser typically used to generate frequency combs in order to scale down cost, complexity and size of the comb generator. The high-Q microresonator, an example of which is shown in the Fig. 1, requires a simple CW pump. Besides being smaller, simpler, and potentially much cheaper, the microresonator has the advantage of producing comb spacings greater than 500 GHz (something unattainable by comb generators that use ultrafast pulsed seed sources like the Ti:Sapph).

(Fig. 2 From Daylight Solutions, interesting molecules arranged by peak absorption wavelength)

One compelling reason for building a comb generator in the Mid-IR is for ultrasensitive, broadband spectroscopy in an interesting spectral region for which there is a dearth of laser sources. Figure 2. from Daylight Solutions (CLEO booth 1526), a company that fabricates quantum cascade lasers between 3.0 and 20.0 microns, sorts molecules of interest by their peak spectral absorbance. These molecules are interesting for environmental monitoring (ozone, water, methane, carbon dioxide), threat and standoff detection (TNT, TATP, VX), and biomedical spectroscopy (glucose).

Similar to the European group's comb generator, PDPA6, "Octave-Spanning Supercontinuum Generation in CMOS-Compatible Silicon Nitride Waveguides, by Halir et al. (Recent MacArthur fellow, Mihal Lipson, is one of the notable et al's on this paper) uses a nanoscale structure, a silicon-based waveguide, to generate an impressive 1.6 octave bandwidth up to 2025 nm on a CMOS compatible platform. Your plug-and-play supercontinuum source is just around the corner! But will it be Windows 7 compatible?

Other postdeadline papers concerned with broadband frequency generation are PDPA5, "Self-Referenced Frequency Comb from a Tm-fiber Amplifier via PPLN Waveguide Supercontinuum," PDPA7, "Spectral Line-by-Line Pulse Shaping of an On-Chip Microresonator Frequency Comb," PDPC9, "Supercontinuum Generation with Self-Healing Airy Pulses," and PDPC12, "Bright Coherent Attosecond-to-Zeptosecond KeV X-ray Supercontinua."

(Fig. 3. From Kobat et al., Optics Exp., 17, 13354, (2009). a) Two-photon image of a mouse cortex with 775 nm excitation and 1280 nm excitation. b) Attenuation of fluorescence vs. depth for 775 nm and 1280 nm excitation.)

New additions to this year's postdeadline session are subcategories in CLEO: Applications and Technology, most notably CLEO: Applications & Technology 1: Biomedical. The four papers in this subcategory demonstrate pushing the limits on resolution, high-speed image acquisition, or penetration depth for different microscopic techniques. PDPB3, "In vivo two-photon imaging of cortical vasculature in mice to 1.5-mm depth with 1280 nm excitation," by Kobat et al. shows record imaging depth in a mouse brain cortex using two-photon microscopy by cleverly using long-wavelength excitation. Typical two-photon microscopes use 800 nm, ultrafast pulses from a Ti:Sapphire laser to excite the tissue to be imaged. Photons may not make it to the depth of interest because of absorption or scattering. In brain tissue, scattering dominates over absorption between 350 nm -1300 nm. By using a longer excitation source, more photons can make it to the target allowing for deeper imaging.

Longer wavelength excitation also means longer wavelength emission, for which there is a decreased absorption due to intrinsic tissue. So by using a 1300 nm excitation source, photons scatter less on the way to the tissue to be imaged, and are absorbed less as the fluorescence makes it way back to the objective lens. Resolution is decreased because of the the longer wavelength, however, tissue can be imaged significantly deeper. Figure 3. shows the difference in image depth using 1280 nm excitation as opposed to 775 nm excitation in the authors' previous 2009 work for which they showed 1.0 mm imaging depth.

These are only some examples of the hot research to be presented at the postdeadline session. After all, there were only 36 accepted papers (they're all hot). Make sure to wear a good pair of shoes, maybe do some some pre-stretching, but most importantly, plan out your postdeadline itinerary by looking at the abstracts. This is one venue where you can be assured every conference attendee will be present.

Civic Scientific Duty

2011-04-07T07:01:00.000-07:00

This is just a short note to emphatically urge any U.S. citizens attending CLEO to sign up and participate in Capitol Hill Day during Thursday May 5, at the CLEO conference. The deadline for signing up is this Friday, April 8. OSA will arrange for you to meet with your district's or state representative(s) so that you can describe the importance of the optics industry, optics and science research, and science education for your state. Your voice is particularly important to prevent harmful or devastating budget cuts to optics, as U.S. congress focuses on ways to cure a ballooning U.S. deficit through budget cuts. Though we may be on different sides of the political aisle, we know that government funding for science research is intimately intertwined with private sector development of cutting edge products. If science and tech funding agencies like NSF, NIH, DOE, DOD, DOC, even USDA (see December FTTH post) take a blow, not only those in academia and government labs will feel it, but the optics industry will as well

OSA will provide training on Wednesday, May 4, at 6 pm for strategies on how to efficiently and appropriately promote science funding to your representatives. On May 5, transportation will be proviced to D.C. via a charter bus. The bus will leave at 8:30 am and return before 5 pm. Because many CLEO attendees might not wish to miss a full day of talks (or might have a talk themselves), OSA recommends the use of a commuter train line from D.C. to Baltimore for those who need to return early.

This is a unique opportunity for scientific civic engagement. Please participate and help keep funding in the optical sciences.

Candy store for Lasers and Electro-Optics

2011-04-05T07:26:00.000-07:00

(Above: Video Interviews with Program Chairs: from CLEO website)

If you haven't been to the CLEO 2011 conference website in the last week (or even if you have), it is worth taking a look at the video interviews with the programming chairs. There are 11 videos addressing the chairs' top picks for talks, their views of trends in optics, advice for conference goers, and their impressions of CLEO's scope and impact for optics research.

In the interviews, the chairs spoke in unison of how CLEO is unique among optics conferences in its breadth of research, particularly spanning basic research to market-ready products. On one hand, you can find talks on fundamental quantum mechanics such as those in the Symposium on the Zeno Effect in Optoelectronics and Quantum Optics whose subject delves into the fundamental nature of measurement. The quantum Zeno effect (or paradox) refers to inhibiting quantum transitions by frequent, repeated measurement. For example, observing an unstable particle in an undecayed state collapses the wavefunction to this state. By quickly measuring it again and again, you can force the wavefunction to repeatedly collapse to the undecayed state by never giving it time to evolve. It never decays, analogous to how Zeno's arrow never hits its mark. So, how could this be used for quantum optics? Besides generically controlling quantum coherence or decoherence of a system, the quantum Zeno effect has applications in optical switching.

On the other hand, in session "Laser Micro and Nano Structuring", in CLEO: Technology and Applications: Industrial, Guido Hennig from Daetwyler Graphics AG, will give an invited talk, AMD4, "Laser Microstructuring and Processing in Printing Industry," discussing the use of high-power fiber lasers for engraving printing plates, as well as high-speed laser modulation for laser-induced ink transfer. In one of the video interviews, Harold Metcalf, from SUNY Stoneybrook, CLEO:QELS Fundamental Science General Co-Chair, aptly characterizes the wide scope of such interesting topics. "Looking over the program and the titles of the sessions, I feel like a kid in a candy store- with unlimited funds, but limited time. It's impossible to do everything," quips Metcalf. To view the "candy store" selection, which I highly recommend as a way of searching for interesting talks you might otherwise miss, go to the conference itinerary planner and click on "Search" and then the "Session Title" drop down menu. You'll be overwhelmed, impressed, and excited.

Some of the specific goodies highlighted by the program chairs in the video-interviews were contributed papers and invited talks discussing UV LEDs, photovoltaics, nanoscale laser sources, metamaterials, broadband spectroscopy, and integrating optics on-chip. Christian Wetzel of Rensselaer Polytechnic Institute, CLEO: Applications and Technology: Industrial Subcommittee Member, points to tutorial ATuD1, "Water and Air Treatment Using Ultraviolet Light Sources," by Gord Knight of Trojan Technologies, as well as invited talk AMC4, "New Concepts and Materials for Solar Power Conversion Devices," by Wladeck Walukiewicz, of University of California, Berkeley, both of which use group III nitride materials in unique ways to develop "green" photonics (Walukiewicz will discuss inserting another band gap within a band gap to increase solar cell efficiency). Seth Bank of University of Texas at Austin, CLEO: Science and Innovations 3: Semiconductor Lasers Alternate Chair, discusses how this year marks the "emergence of the the nanolaser" and recommends tutorial talk CTuG1, "Nanoscale Lasers: How Small Can they Go?" from Shun Lien Chuang of University of Illinois, Urbana-Champaign as well as device results from invited paper CTuG2, "Room Temperature CW Operation of Metal-Semiconductor Plasmonic Nanolasers with Subwavelength Cavity." Tim Carrig of Lockheed Martin, CLEO: Science and Innovations General Co-Chair, and CLEO: Applications and Technology General Chair, projects now will be the time that companies need to look at the fundamental research on optical metamaterials to begin understanding how to make market-ready products in the near-future. For introductory information on metamaterial applications, a good place to start will be tutorial QTuM1, "Optical Metatronics" from Nader Engheta from University of Pennsylvania.

The suggestions of talks and lists of recommendations from the chairs goes on. To find out more, click on the program chair video link on the CLEO main page.

CLEO Technology Sparks Controversy

2011-03-17T21:31:00.000-07:00

(Left: Data points from Osram Opto Semiconductor of Germany. Lower black square at 142 lm/W demonstrating record white-light LED efficiency; second black square at 160 lm/W shows projected efficiency after further optimization.)

You may not think that LED lighting would be a controversial topic, but as the New York Times reports, it may be indirectly responsible for new anger among conservative lawmakers in the United States. A U.S. federal law passed in 2007 by the Bush administration will, among other energy-saving measures, make the sale of the incandescent 100-watt light bulbs illegal in 2012. Republican representatives Joe Barton of Texas and Michelle Bachmann of Minnesota, and Republican Senator Rand Paul of Kentucky have recently become vocal about the rights of Americans to purchase lighting of their choice (energy-efficient or not).

The alternatives to the more-than-a-century-old technology spurning this debate are a new make-over of halogens (not much more efficient than incandescent bulbs at about 20 lumens/W), compact fluorescent bulbs (about70 lumens/W), and LED lighting (Osram Opto Semiconductors of Germany just recently claimed to have set a record for warm-white LED chips at 142 lumens/W). CLEO attendees beware: might tea-party members be planning protests of sessions within CLEO Science and Innovation 15: LEDs, Photovoltaics and Energy-efficient ("green") Photonics?

The "controversial" talks related to LED lighting can be found specifically in sessions "Nano-structured LEDs" on Monday, May 2, 1:30-3:15 pm and "Toward More Efficient Visible LEDs" on Wednesday, May 4, 1:30-3:10 pm. Many of these talks will address specific problems in the overarching goal of fabricating highly-efficient LEDs that can simultaneously mimic the white-light spectrum of an incandescent light bulb. White-light LEDs could reach luminous efficiencies of greater than 300 lumens/W once certain device and fabrication challenges are overcome.¹

One of the greater challenges is overcoming the emission gap in the green-yellow region of the visible spectrum (515-600 nm).^1,2 Whether multiple LEDs of different color are combined to produce white-light, or one or two different colored LEDs are used to pump phosphors to produce white light, current designs lack efficient production of yellow-green photons for true white-light color (a stinging irony for a technology slated as "green" photonics). Invited talk, CMU5, "Nitride-based Nano-columns and Applications" and contributed paper CMU6, "Diffraction-Coupled Plasmon-Enhanced Light Emission from InGaN/GaN Quantum Wells" in session "Nano-structured LEDs"will show different approaches to generating green light using nano-structures on InGaN. Lowering the dimensionality by using nano-structures allows one to play with defect, strain, and polarization properties of the material and hence light generating capability and extraction.²

Another challenge being addressed in session "Toward More Efficient Visible LEDs" is "efficiency droop" particular to InGaN. InGaN LEDs show great promise at low currents, but suffer an enormous efficiency reduction (the droop) at high-current injection, a problem for potential use in high-power applications. The jury is still out on the cause for the droop.² Contributed paper CWF3, "On the symmetry of efficiency-versus-carrier-concentration curves in GaInN/GaN light-emitting diodes and relation to droop-causing mechanisms" will be presenting evidence in support of carrier-leakage theory for droop. Contributed paper CWF4 "Efficiency Droop Reduction in InGaN/GaN Light-emitting Diodes by Graded-thickness Multiple Quantum Wells" will show work demonstrating droop reduction by inserting clever nano-structures into the design.

Whether or not you personally believe you should have the right to buy old-tech, 100-Watt incandescent light bulbs, one thing that is not a controversy is that LED technology is hot. It will likely be the future of lighting for illumination and displays. Don't miss out on these talks.

References

1. E Schubert and J.K. Kim, "Solid-State Light Sources Getting Smart," Science, 308, 1274-1278, (2005).

2. M. Crawford, "LEDs for Solid-State Lighting: Performance Challenges and Recent Advances," J. Sel. Topics in Quant. Electron., 15, 1028-1040, (2009).

Thoughts go out to our Japanese Colleagues

2011-03-14T07:47:00.000-07:00

I know I am not alone when I write that my thoughts go out to our Japanese colleagues, collaborators, and friends as they cope with the aftermath of the March 11, earthquake and tsunami. The field of optics has a rich history of Japanese innovation. CLEO habitually hosts a significant number of contributed papers, tutorials, short courses, and plenary talks from Japanese scientists or those with ties to Japanese universities or companies. I hope for the safety and health of the survivors of this horrific disaster, and for what it may be worth, offer condolences to those who lost friends, family and loved-ones.

I am optimistic that the recent crises involving nuclear reactors will be solved without further disaster. My experience with Japanese technology and expertise is that it is thoughtful, long-term, and state-of-the-art. If anyone can come up with the right solution, it is them.

James Bond meets CLEO

2011-03-04T07:51:00.000-08:00

(Above: From LLNL, Artist's concept of the MEGa-ray system)

The conference program for CLEO 2011 was just released on Wednesday, March 2. Among many other cutting-edge and ground-breaking contributed papers are those from the new conference to debut this May, CLEO: Applications and Technology. Browsing the topic subcategory, Lasers for Government Science and Security Applications, I came across titles that seemed to be the stuff out of a James Bond movie, ATuF2, "Mono-Energetic Gamma-rays (MEGa-rays) and the Dawn of Nuclear Photonics" and ATuF4, "2D+3D Face Imaging for Stand-off Biometric Identification." Can't you just picture the mad, evil-scientist-villain (disfigured in some way, stroking his cat) plotting to steal a MEGa-Ray device in one scene, and Q 3D-scanning 007's face in order for him to gain access into MI6 in another? Maybe I need to do more optics research and watch less movies, however, there's no question about impact of these papers.

Last February, David Gibson, Christopher Barty and colleagues at the National Ignition Facility and Photon Science Division at Lawrence Livermore National Laboratory (LLNL) published their initial results on a MEGa-Ray source they constructed as groundwork for a beefier machine (2 MeV) in the future. At 2 MeV, such a narrow-bandwidth, high-energy, x-ray source could provide brightness 15 orders of magnitude greater than those produced by synchotrons. The artist rendition of the facility shown in the figure above demonstrates the compact size (a large room) compared to the kilometer-scale rings or linacs conventionally used for generating high energy x-ray beams. Additionally, x-rays of this energy and brightness will find use in nuclear physics and applications such as detection of concealed nuclear material or specific isotope detection and quantification.

So how do you make a MEGa-Ray? By scattering high-intensity laser photons off of a relativistic electron beam (Compton Scattering). In fact, the relativistic electrons are made with a laser as well. The group at LLNL uses matched fiber laser oscillators and fiber-based amplifiers to make the relativistic electrons and the high-intensity scattering light to produce the end product.

Brian Redman from Lockheed Martin and his collaborators, on the other hand, are using light in a very different way- to scan human faces for secure identification and threat-detection. Biometric identification refers to a technique in which a subject can be identified by a unique physical trait or something they physically produce. Some examples are fingerprinting, iris scans, facial scans, and analysis of gait. This topic is particular fascinating to me since human identification is something that the human brain does remarkably well, and for which computers often have trouble. We can identify another person with a great success rate from a far distance based on how they walk, their gait (for a fun gait simulator click here). We have an impeccable ability to identify faces, particularly when we are young- babies can recognize different monkey faces. Therefore one of the directions of research on biometric identification is to improve computational algorithms.

One of Lockheed's specific objectives in their partnership with the FBI is to build a database of facial scans analogous to their database of fingerprints, the Integrated Automated Fingerprint Identification System (IAFIS). I look forward to hearing how Dr. Redman's CLEO talk addresses the optics involved in the facial scans, the use of both 2D and 3D scan information, and the success of the algorithms employed.

Femtomagnetism and Phototherapy

2011-02-23T11:26:00.001-08:00

(Left: Schematic of pump-probe experiment to investigate femtosecond time-scale demagnetization on a magnetic film; from Bigot et al., Nature, 465, 458 (2010).)

As we await decisions on contributed papers in the next couple of weeks and for the technical program to be scheduled, the list of tutorials and invited talks for CLEO 2011 is rounding out. Two provoking titles that recently caught my eye were tutorial talks "Femtomagnetism" to be given by Jean-Yves Bigot from CNRS in Strasbourg, France under CLEO: QELS Fundamental Science 4: Optical Interactions with Condensed Matter and Ultrafast Phenomena as well as "Therapeutic Applications of Light: Photodynamic Therapy, the Killer and Low Level Light Therapy, the Healer" to be given by Michael Hamblin from Massachusetts General Hospital, under CLEO: Applications & Technology 1: Biomedical.

Femtomagnetism refers to magnetization dynamics which occur on a femtosecond time-scale. Over the last decade, Dr. Bigot and his colleagues have been using ultrafast laser pulses to induce changes in the magnetization of ferromagnetic materials on unprecedented time-scales. Besides probing the fundamental nature of magnetism, this work provides insight into the future of magnetic data storage, particularly finding a way to increase the speed of recording data. A ground breaking paper Phys Rev Lett. in 2007, by Stanciu et al. showed how the previously-thought fundamental speed limit to magnetic data recording could be broken by using ultrafast laser pulses to reverse the magnetization of magnetic bits during writing.

In a recent Nature article, Bigot et al. describe short time-scale, spin-orbit dynamics during femtosecond, laser-induced demagnetization. Using a femtosecond pump pulse to quickly demagnetize a ferromagnetic thin-film immersed in a magnetic field, Bigot and his collaborators extract information about the spin and orbital angular momentum as a function of time in a cross-correlation technique using x-ray pulses (See Fig.1). Spin and orbital angular momentum contributions during the process are measured by time-resolved x-ray magnetic circular dichroism (XMCD), a technique in which circularly polarized x-rays absorb in different proportions at different energies depending on the spin and orbital angular contributions of the material. This recent work investigates the magnetism dynamics in thin films whose magnetization is perpendicular to the plane of the film- a class of materials sought after for high-density data storage, and for which spin-orbit coupling plays a large role.

After reading some background on this fascinating and complex work, I was reminded of a famous interview with Richard Fenynman where a BBC reporter asks him to explain magnetism (click here to see the youtube clip). In Feynman's clever way he basically tells the reporter he can't do it because there is nothing in the reporter's sphere of knowledge and experience that would help him understand. Magnetism is beautiful, complicated, and at the fundamental quantum level, extremely non-intuitive (you really can't get by on analogies of spinning tops and orbitting planets, that's just plain wrong). If like me, you need some background, a good start is Bigot's 2002 review paper. Of course, why not hear it from the horses mouth and mark the tutorial on your conference planner.

(Above: plots showing enhanced cellular uptake of the photosensitizer ZnPc-(Lys) compared with other sensitizers, and corresponding images of cells; from Hamblin et al., ChemMedChem, 5, 890, (2010).)

Professor Hamblin's work on the other hand uses light in a very different way- to activate chemicals that can target and selectively kill harmful cells like infectious microbes or malignant cancer cells (photodynamic therapy), as well as to activate the production of intrinsic detoxifying chemicals within damaed cells to stimulate tissue healing (low level light therapy). In photodynamic therapy (PDT), photosensitizers are introduced into the body locally or topically and taken-up by the harmful cells. Illuminating the targeted cells with light excites the photosensitizers and produces reactive oxygen species harmful to the targeted cell.

(Above: Table showing inhibition of tumor growth when using photodynamic therapy with ZnPc-(Lys) ; from Hamblin et al., ChemMedChem, 5, 890, (2010).)

One of the aims of Hamblin's group is to create more efficient photosensitizers- ones that are more readily taken up by targeted cells and that are more lethal. Hamblin recently synthesized a photosensitizer, Pentalysine Be ta-Carbonylphthalocyanine Zinc (ZnPc-(Lys)), that showed better cellular up-take, better selectivity to targeted cells, and a 20 times increase in photo-toxicity. Figure 2. shows the increase in uptake compared to conventional sensitizers and Table 1. shows the results of tumor-growth inhibition in Kunningmig mice that were treated with PDT using ZnPC-(Lys). For more information on killing and healing power of light, visit Professor Hamblin's very accessible and informative web pages. Better yet, be sure to attend the tutorial on phototherapy!

Stand Up and Clap if you Love Science!

2011-01-27T13:22:00.000-08:00

(Above: U.S. President, Barack Obama, following-up his state-of-the-union message at energy technology firm Orion Energy Systems in Manitowok, WI on January 26. Photo from Orion Energy Systems)

Just this past Tuesday, U.S. president, Barack Obama, invoked science and innovation in the State-of-the-Union-Address, as the silver bullet to heal an ailing U.S. economy and crumbling infrastructure. U.S. statesmen and -women alike got up out of their seats repeatedly to give applause for science. Specifically, Mr. Obama, cited three optics-related areas of research to which he will try to allocate U.S. federal funding: 1) biomedical research, 2) information technology, and 3) clean-energy technology. Mr. Obama proposed to send a budget to congress in the next few weeks that would help the U.S. "...reach a level of research and development we haven’t seen since the height of the Space Race." To that aim, CLEO will be hosting contributed papers in these three areas, and if Mr. Obama is successful in his budget requests, perhaps we will be seeing more submissions and exhibitions in these fields in the near-future.

Entire sessions devoted to Obama's first research area, biomedical research, can be found under two-topic categories CLEO:Applications and Technology 1: Biomedical and CLEO: Science and Innovation10: Biophotonics and Optofluidics. The former will contain research already in the clinical-trial stage, whereas the latter will hold emerging research that is "pre-pilot." One of the many sub-categories in these topics includes optical biopsy. The goal of optical biopsy is to diagnose tissue during a medical procedure in vivo with photons rather than extracting it invasively with a knife (to be analyzed later in a lab). This is the aim of many biomedical techniques such as diffuse optical tomography (DOT), optical coherence tomography (OCT), and multiphoton microscopy (MPM). These techniques use light in clever ways to extract information from deep inside tissue which typically scatters away all the light you want. Be sure to attend these sessions for the latest on these and other emerging biomedical techniques.

Sessions for Mr. Obama's second research area, information technology, can be found under topic categories CLEO: Science and Innovation 12: Lightwave Communication and Optical Networking, CLEO Symposium on Quantum Communications, and CLEO: Science and Innovation 9: Components, Integration, Interconnects and Signal Processing. One of the invited talks in the special Symposium on Quantum Communications will be from Masahide Sasaki of NICT, regarding the Tokyo Quantum Key Distribution (QKD) Network. Just this past October, a secure video (a record megabit per second data rate using QKD) was demonstrated over the Tokyo QKD Network at the Updating Quantum Cryptography and Communications conference. Be sure to attend Dr. Sasaki's talk on the current and future state of secure photonic networks.

Finally, sessions regarding Mr. Obama's third area of research, clean-energy technology, can be found under topic categories CLEO: Science and Innovation 15: LEDs, Photovoltaics, and Energy-efficient ("Green") Photonics, and CLEO: Applications and Technology 2: Environment and Energy. One of the sub-categories, photovoltaics, will be discussed at the research stage in the first category, and their practical production and implementation in the second. Some of the issues concerning photovoltaics are reducing production cost while increasing power conversion efficiency. Simple silicon is cheap, but only gives efficiencies in the range of 10-18% for ambient sunlight. Using tricks to expand the spectral response in the UV and infrared can be done by incorporating multiple materials. Concentrix of Germany, manufactures a triple-junction cell (GaInP/GaInAs/Ge) that produces efficiencies up to 38%. Production is more expensive than a single silicon p-n junction, however, by incorporating a Fresnel lens on the surface, less material is needed, and cost can be significantly lowered (see Nature Photonics, "Concentrating on the Future") . Other tricks to up efficiencies can be used such as "quantum-cutting" (either down-converting UV light into redder light or using two-photon absorption of infrared photons), texturizing the surface to minimize reflection, or incorporating nanostructures to increase light harnessing capability through plasmon response (see Nature Photonics, "Sunny Outlook"). Come to these sessions to learn about the latest research, not just in photovoltaics, but in other areas of "green" photonics. If Mr. Obama has his way "by 2035, 80 percent of America’s electricity will come from clean energy sources." If the U.S. reaches this goal, it will be the very technology presented at CLEO that will have brought us there.

Fiber-to-the-home and Science Innovation

2010-12-30T22:19:00.000-08:00

(Left: Fiber-to-the-home converter box at my mother-in-law's rural Wisconsin home. The optical signal is converted into an electrical signal at the box and then routed into the house. The black cable is the input optical fiber bundle; if you squint, you can make out some additional yellow-jacket, fiber patch-cords through an opening at the base of the box.)

Like usual, this Christmas holiday my family and I spent some time at my mother-in-law's rural home in Spring Valley, Wisconsin enjoying good food, fresh air, and the escape from the confines and bustle of city-living. However, what was different about this year's visit was her home's new Terabit/s capacity for current and future digital communication and entertainment needs. My mother-in-law lives in one of six million American homes that currently have Fiber-to-the-home (FTTH) connectivity.

Her service provider, West Wisconsin Telecom Cooperative, is part of a growing number of American rural telecoms and municipalities surpassing their urban counterparts in the future of lightwave communications. Much of this rural technological growth has been made possible through grants and low-interest loans from the United States Department of Agriculture (USDA) Rural Utility Service (RUS) Telecommunications Program whose aim is to improve education, health, and economic opportunities of rural families and businesses through broadband internet access.

(Above: The neighbor's farm across the street .)

Seeing and using FTTH in person at my mother-in-law's got me excited about its implications on photonics research and applications, and science in general. Though CLEO is not a telecom- centered conference like OFC (optical fiber communications conference), there is much that fundamental science and optics research can leverage from telecom technology and visa-versa. The growth in one field breeds growth in the other. For a nice paper about the symbiotic relationship between great physics discoveries and advances in telecommunications technology, see Brinkman and Lang's 1999 Reviews of Modern Physics paper "Physics and the Communications Industry."

Though I may be biased towards fiber-based technologies, to me the links between work presented at CLEO and the growth of telecom is pervasive. For starters, the first CLEO plenary speaker, Donald Keck, will share stories of how his team at Corning pioneered the first usable low-loss fiber in 1970 and discuss its place in the broader context of the ensuing optical technology and information revolution. The exciting history of bringing down the loss of optical fiber (which in its infancy was an opaque 1000 dB/km) involves a Nobel prize (Charles Kao correclty hypothesized the bottleneck to transparency) and the development of the groundbreaking fabrication technique of modified chemical vapor deposition (MCVD) by John MacChesney's team at Bell Labs, which brought loss down to what it is today.

As Keck will likely discuss, making fiber transparent paved the way not only for a host of other telecom and information technologies but new fields of photonics. For communications, once you have an acceptable waveguide, you still need sources, modulators, detectors, amplifiers, routers, multiplexers, switches. For the most recent breakthoughs in telecom be sure to attend CLEO: Science and Innovation 12: Lightwave Communication and Optical Networking.

Naturally, the field of quantum communications is tied up in current telecom technology. CLEO Symposium on Quantum Communications will host papers in both fundamental science research in quantum information and actual quantum communication testbeds- fiber-based and free-space.

You can find telecom-derived technology in CLEO: Science and Innovation 11: Fiber Amplifiers Lasers and Devices. This session includes topics such as CW and pulsed mode-locked fiber oscillators, amplification in doped fibers, ultra-wideband fiber amplifiers, Raman amplifiers, coherent and incoherent combination of fiber lasers and amplifiers, fiber-based nonlinear effects, fiber-grating and microstructured fiber devices. The applications for these technologies range from spectroscopy, biomedical imaging, and materials processing.

(Above: Sign marking the location of buried fiber)

My excitement at my mother-in-law's FTTH led to some disappointment about the speed of her computer (any computer for that matter). She has ~100 Tb/s capacity, but only ~Gb/s capability. To get the capability you need to move to all-optical signal processing and optical computing. CLEO will host a variety of sessions regarding or related to this important technological goal. See CLEO-QELS Fundamental Science 6: Nano-optics and plasmonics; CLEO: Science and Innovation 7: Nano-optics Micro- and Nano-photonic devices; and CLEO: Science and Innovation 9: Components, Integration, Interconnects and Signal Processing. Among other ground-breaking research, I anticipate contributed papers from the Cornell Nanophotonic's Group whose P.I., Michal Lipson, recently received a MacArthur Genius Award , ($500k no strings attached) for her pioneering work in silicon-based circuits for practical optical computing.

The list of sessions at CLEO inspired by optical fiber and telecom technology goes on. One of my hopes for 2011 is to witness FTTH to more of the country, rural and urban. This isn't just job security for us all, but may prove pivotal to the growth and expansion of innovation in optics and science.

Emerging THz technology could solve body-scanner controversy

2010-11-23T20:44:00.000-08:00

Above: From TeraView press release Jan. 2010, THz Spectra of explosives (threats) and different clothing materials (non-threats).

Today, the day before Thanksgiving, is one of the busiest holidays for air-travel in the U.S. The latest hubbub in U.S. airport security is the use of x-ray body scanners to detect for potential explosives or weapons carried by passengers. The scanners spray the traveler with soft x-rays and then detect the back-scattered radiation to produce an image of the passenger, minus his or her clothing. Many travelers have found this new level of security too invasive and have opted out for the traditional pat-down. Others have used their experience as the "butt" of jokes; Humorist Dave Barry recently described his ordeal of going through airport security of having both the scan and a pat-down due to a "blurry groin area" from the image. The threat of body-scanner boycotts from various websites and blogs prompted transportation security administration (TSA) chief John Pistole to plead to holiday-travelers to put security needs above personal modesty since the pat-down takes much longer and will lead to travel delays, inconvenience, and economic hardship for the travel industry.

The first thing that came to my mind in the flurry of stories I've been hearing regarding body-scanners and privacy issues was Terahertz (THz) radiation. Though I don't remember the particular conference, I still have the images in my head from a THz radiation talk not long after the Columbia Space Shuttle disaster in 2003 of space-shuttle foam and a body-scan. The presenters were using these images to motivate the applications of THz radiation for imaging- the THz image of the foam as a nondestructive technique to look at the structural integrity of shuttle foam, and the THz image of a body-scan as a better control of threat-detection in airports. Thz radiation was a budding field at this time and has since exploded. Last CLEO conference there were nine different sessions involving THz research and applications. Sessions ranged from new THz sources and detectors to THz waveguides and metamaterials. At the 2010 postdealine session, Xi-Cheng Zhang's group of Rensselaer Polytechnic Institute (likely the same group whose space shuttle foam and body-scan I remember from 2003) presented a paper on remote sensing using broadband THz sources.

One of the reasons the 2003 images stuck in my head was that the body-scan model was wearing what I assumed to be some kind of metallic underwear. What makes THz radiation useful for a body-scan is that it is readily transmitted through non-metallic and non-polar materials like clothing. Obviously the model for this research shared the same concerns as many current U.S. travelers. However, there is more to THz imaging than just seeing through clothing which could make THz scanners both a more effective and less invasive tool than x-ray scanners.

Unlike x-rays, there are a number of explosive, chemical, and biological agents of interest for threat-detection that have characteristic THz spectra¹, including PETN which was found in the "underwear bomber's" briefs after his foiled attempt to blow-up a plane near Detroit last Christmas. Rather than build up an image of the body and rely on the scanner operator to judge the potential threat from visual inspection, a THz scanner could look at the reflected spectra point-by-point to compile a molecular fingerprint by comparing to a database of absorbance spectra. Effectively, this technique is "THz spectroscopy through clothing". You build up a chemical map across the body instead of a body image. TeraView of Cambridge announced work on such a scanner last January when the U.K. ran into similar passenger discontent over x-ray body-scans. Besides giving travelers back their modesty, this technique likely could give better threat detection as well as less false-positives since threats are identified chemically instead of visually.

To find the latest breakthroughs on THz scanners, be sure to attend sessions under CLEO: Science & Innovation: Terahertz Technologies and Applications, or CLEO: Applications & Technology: Government & National Science, Security & Standards Applications this May. Until then, have happy, safe, and hopefully noninvasive travels.

References

1. J. F. Federici et al., "THz imaging and sensing for security applications-explosives, weapons, and drugs," Semicond. Sci. Technol., 20, S266-S280, (2005).

Your mother may think you're special, but does CLEO?

2010-10-31T15:18:00.000-07:00

Above: reproduced from Ref. 1. Magnetomotion OCT (MM-OCT) of chicken breast tissue.

CLEO conference organizers recently posted the categories for the Special Symposia which are to include five areas: 1) Nano-bio-photonics, 2) Broadband Spectroscopy: New Techniques and Sources, 3) Quantum Communications, 4) Fiber Parametric Devices and Applications, and 5) Light-emitting Nano-plasmonic Devices.

Among other invited speakers in the Nano-bio-photonics Symposium, Stephen Boppart from University of Illinois, Urbana-Champaign, will be discussing "Endogenous Molecules or Exogenous Molecularly Targeted Contrast Agents for OCT." OCT, or Optical Coherence Tomography, was pioneered in the early 1990's by James Fujimoto of MIT, who will also be giving an invited talk in this Symposium. OCT uses the cleverness of interfering low-coherence light to scan through tissue to depths up to a few millimeters and with an axial resolution equivalent to the coherence length of the source, typically less than 10 microns. Complete OCT setups can be purchased commercially, like Thorlab's OCS1300SS. In fact, during my last eye-checkup I asked my optometrist if she had heard of OCT since they are becoming more widely used by opthamologists to probe retinal health and conditions. She did. In fact she had participated in a clinic to understand how to use OCT and read images.

Though roubst, OCT has been limited to a small number of medical applications because it is insensitive to standard molecular probes used by biomedical researchers such as fluorophores or bioluminescent markers. This is because fluorescence and bioluminescence arise from inelastically scattered light, and OCT is sensitive only to elastically scattered light (light coherent with the source). Therefore, in order to use molecular probes with OCT to diagnose a wider variety of diseases or to answer fundamental questions of cellular function, one must use a different set of probes that are sensitive to elastic scattering properties of light like changes in scattering itself, absorption, polarization, phase, or frequency.¹

From the title of the talk, I imagine that Professor Boppart will be discussing some of the exogenous probes (probes introduced into the tissue) he and his group have created and used for OCT like metallic nanoshells and microspheres engineered from a variety of materials to enhance scattering.¹ My favorite of the ingenuous probes are particles with high magnetic susceptibilities such that when modulated with a magnetic field, their subsequent motion changes the local scattering properties of the tissue, see the figure above.¹ I also suspect he will be talking about endogenous probes (where the tissue of interest naturally contains helpful probes) like collagen that can be stimulated by a coherent process like second harmonic generation, or Hb/HbO2 whose scattering and absorbing properties are frequency-dependent.¹ I'm excited to hear advances in this work as well as attend the other symposia.

The latter four symposia are open for submission of contributed papers and you can find the CLEO or QELS subcategory to which to submit beneath the particular symposium description. I'm particularly interested in the Broadband Spectroscopy Symposium since one of the emphases is Mid IR sources, a new interest of mine. I also am excited that the Quantum Communication Symposium, which like the Nano-bio-photonic Symposium, has been placed under the designations of QELS: Fundamental Science, and CLEO: Science and Innovation, and CLEO: Applications and Technology. These symposia will attempt to show their fields from the idea-stage all the way to commercialization.

So if you think you're special (which if you're planning on submitting work to CLEO you most certainly are), take a moment to see if your work falls into the Special Symposia categories.

References

1. S. A. Boppart et al., "Optical probes and techniques for molecular contrast enhancement in coherence imaging ," Journal of Biomedical Optics, 10, 041208, (2005).

Call for Papers and CLEO's New Direction

2010-09-27T11:07:00.000-07:00

As the leaves are changing color and the days are becoming shorter, it's time to get your CLEO submission into shape. Time to order those parts with long lead-times. Time to optimize your code. Time to hunker-down, build your experiment and collect data. And this time, perhaps even demonstrate your prototype.

This Thursday marks the official Call for Papers for CLEO 2011 in Baltimore. The deadline for submissions (with the exception of post-deadline papers) is December 2, 12:00 pm EST. For your convenience, and hopefully not to stress you out, I've embedded a countdown timer at the top of the blog.

CLEO 2011 will prove to be even more exciting this coming May due to the addition of a new conference, CLEO: Applications and Technology. The classic CLEO conference, CLEO: Science and Innovation and CLEO/QELS: Fundamental Science, will still remain intact. The new conference will "explore the intersection of academic research with product commercialization." Papers submitted to the Applications and Technology conference will demonstrate the transition of fundamental and applied research toward product commercialization. The conference programmers emphasize work should be pre-commercial. Topic categories include Biomedical, Environment/Energy, Government and National Science, Security and Standards Applications, and Industrial.

The addition of CLEO: Applications and Technology, to classic CLEO, QELS, Market Focus, and the Expo gives continuity to the spectrum (no pun intended) of innovation at the conference. Under one roof conference-goers will now be able to learn about break-throughs in fundamental science (QELS), applied science (CLEO), the transition of applied research to commercial products (Applications and Technology), commercial developments and research ready-for-commercialization (Market Focus), as well as see and purchase commercial products first-hand (Expo).

In my opinion, the move to foster more collaboration and communication between fundamental research and product development is wholly positive. I recently showed my electronics class the NOVA special Transistorized which recounts the development of the transistor. The history of this device that revolutionized all of our lives shows how synergy between commercial enterprise and fundamental science can produce both Nobel laureates and corporate behemoths like Sony and Intel. Let's hope history repeats itself in Baltimore.

FiO/LS 2010: Everything and the Kitchen Sink

2010-09-27T02:18:00.000-07:00

Karl Koch of Corning, Inc., and this year's General Program Chair for Frontiers in Optics 2010 Annual Meeting, is not fibbing in the slightest when he says FiO "..covers almost all topic areas that the Optical Society concerns itself with." Where else could you find sessions like Astrophotonics, Vison and Color, Optical Design with Unconventional Polarization, Laser-based Particle Acceleration, Lasers for Fusion and Fast Ignition, and Sensing in Higher Dimensions all in the same program?

This year's conference is being held in Rochester, NY during October 24-28. Whether attending or not, be sure to catch up with FiO bloggers Laura Waller and Stephen Roberson for daily conference updates. Besides the breadth of topics, what makes FiO/LS special is a smaller, more intimate atmosphere than the typical conference fare. Quality has not been sacrificed for breadth. This years conference includes presentations by heavy-hitters such as Emil Wolf, James Gordon, Stephen Block, Jim Fujimoto, Sunney Xie, Alain Aspect, and many more.

To help build your specific conference itinerary, I recommend watching the you-tube shorts of the different subcommittee chairs describing work in their particular topics. I found Alfred U'Ren's, of Universidad Nacional Autonoma de Mexico, descriptions of Quantum Electronics abstracts (above) particularly helpful. Among other talks, Dr. U'Ren highlighted work by Stephen Barnett, FTuZ1, "The Enigma of Optical Momentum," in which Barnett seems to have solved a longstanding paradox between conflicting descriptions of optical momentum in materials. Through a combination of browsing the shorts and looking at the online planner, I also became interested in FTuS7, "Tensile Strength Analysis of Laser Skin Welding with Thulium Laser System," whose authors are seeking a photonic replacement to suturing wounds using Mid-IR light.

Though the plenary is typically a staple, I still feel compelled to urge you to attend Joseph Eberly's Ives Medal Address. Dr. Eberly will be receiving OSA's highest honor. His talk, "When Malus Tangles with Euclid, who Wins?" stands to be creative and enlightening.

Finally, another unique quality of FiO/LS is an emphasis on education in science and optics. Science Educators day, Wednesday, October 27, 4:30-8:00 pm, is a chance for middle and high school educators, professional or volunteer outreach, to learn new hands-on demos and experiments in optics for the classroom. Additionally, FiO/LS is one of the few professional optics conferences that has an undergraduate symposium, Monday, October 25, 12:00-6:30 pm. FiO/LS is leading the way to mentor and encourage the future generation of optical scientists and engineers. Mark your calendars and support these budding, young scientists.

Oh what an entangled web we weave...

2010-09-07T20:41:00.001-07:00

(Above: The nerdy license plate of fellow Augustana College physics professor Cecilia Vogel, referencing the famous 1935 Phys. Rev. paper by Einstein, Podolsky, and Rosen which introduced the idea of entanglement and questioned the completeness of a quantum mechanical description of reality)

Looking back through some of the literature in photonics and optics published this summer, I was most fascinated by three experiments concerning reliable generation of entangled photons. Two groups, one from China¹ and another from Vienna², showed independent reports of heralded generation of entangled photon pairs. Another, from Toshiba of Europe , demonstrated 'on-demand' entangled photons from a quantum dot embedded inside an LED, making an entangled-LED or more simply, ELED³. These works have been nicely summarized in the News and Views section in the August issue of Nature Photonics: “Entangled photons report for duty,” by Pieter Kok⁴ and “A spooky light-emitting diode” by Val Zwiller⁵ .

For me, quantum entanglement may be one of the coolest and weirdest properties of light. Entanglement ‘spooked’ Einstein and led to a paradigm shift in our fundamental understanding of the nature of measurement and reality. Particles of matter or light don’t live in well defined states until we force them to by a measurement. This is already weird, but now if they are entangled, the measuring process is shown to be nonlocal–a measurement on one particle simultaneously determines the state of the other.

As a young graduate student, I found myself filling up conference itineraries with talks on quantum computing, cryptography, and key distribution. My head spun with trying to understand all the bras and kets that accompanied explanations of quantum information protocols. Admittedly, I should have paid better attention in modern physics and quantum mechanics when I was a student (sorry professors Vogel, Coppersmith, and Drell!). However, frustrated with Alice, Bob, and that pesky Eve, my reaction was to give up, and since my research dealt with large numbers of photons, I decided to happily and naïvely live in a classical world.

The recent News and Views articles by Kok and Zwiller stirred the inner physicist within me, and sent me down a path of literature searching too detailed, too mathy , and too long for a blog post. However, I’ve attempted to give my own understanding of how the exciting work of heralded and on-demand entangled photon sources can be put into a broader context. If you’re a beginner like me and want more information on the fundamentals of quantum information, I recommend Kok’s website and review article⁶, Gisin’s review⁷, and Dehlinger’s article geared for setting up entanglement experiments for the advanced undergraduate laboratory curriculum⁸.

Whether or not you’re a practicing quantum mechanic, you likely know that entanglement is a crucial ingredient for quantum information processing. Entanglement using photons may be the best method for practically achieving quantum computing and for quantum communication due to their coherence, low transmission loss, and ease of manipulation. The most widely used method for generating entangled photon-pairs is through spontaneous parametric down-conversion in a nonlinear crystal (SPDC). This technique is so robust that it has recently been employed in a number of undergraduate teaching labs to help physics students understand the photonic nature of light and the non-intuitive implications of quantum mechanics^8,9,10.

Beating the odds

The problem with SPDC is that the process of pair generation is probabilistic. More often than not, zero or multiple pairs are generated, see Fig 1 (a). Like a game of black-jack at a Vegas card table, more often than not you don’t get the cards want, and so more often than not, the house wins. However, if you are clever and can count cards, you can guarantee a win even though the odds are against you. You aren’t changing the probability distribution of what is being dealt, you are just predicting what will be played. You can select which cards you want and pass on others without having to see their face values. In the language of quantum entanglement, you would be 'heralding' or announcing the cards you want before they are dealt.
Figure 1. reproduced and adapted from ref. 4. Creating entangled photon pairs. (a) In normal operation, a parametric down-converter (PDC) produces an unknown number of entangled photon pairs in each pulse. Detectors must then ‘post-select’ the correct events that contain exactly one pair. (b) The basic setup used by Pan and Walther's lab; a particular four-photon detection event can occur only when three pairs are present, with the remaining two entangled photons propagating freely. This creates precisely one ‘heralded’ entangled photon pair.

The heralded entangled photon source produced by Jian-Wie Pan’s lab in China¹ and Philip Walther’s lab in Vienna² was done through clever counting. Both groups used a setup similar to Fig 1. (b) such that when three photon pairs were generated simultaneously by SPDC, two of the pairs would be ‘peeled off’⁴ by the beam splitters, and remaining would be guaranteed to be a single entangled pair. Essentially, the simultaneous firing of four detectors at the outputs of the ‘peel off’- beam splitter herald a single remaining entangled photon pair. You have to wait for a three-photon pair event, but you can be guaranteed an entangled output.

Fig. 2 (a) Reproduced and adapted from from ref. 3. Schematic of the active region of the ELED, showing the emission of a polarization entangled photon pair through the biexciton cascade. (b) reproduced from ref. 5. Optical microscope image of the from Toshiba Europe.

Another way to beat the house is to change the probability of cards drawn- use your own deck. Salter et al.³ from the Shileds group of Toshiba Europe essentially took this approach to creating entangled photon pairs by using an entirely different physical mechanism than SPDC. Using the radiative decay of the biexciton state in a quantum dot Fig. 2 (a) , the Toshiba group created an ‘on-demand’ entangled source. The biexciton state is created by the capture of two electrons and two holes. So long as the two excitons are degenerate in energy (no fine structure splitting) the output will be entangled. In fact, one of the experimental hurdles overcome by the Tohsiba group was to grow quantum dots emitting photons of the right energy, near 1.4 eV (887 nm), in order to have very small fine-structure splitting. Because the source is not probabilistic and no clever counting setups are needed, it is referred to as ‘sub-Poissonian’⁵. What makes Salter’s work so hot is that the on-demand source is driven electrically. No bulky pump lasers are needed like they are for an SPDC source. The entangled-LED, or ELED, could possibly be scaled down to submicron sizes for on-chip integration⁵, see the microscope image in Fig. 2 (b).

Limitations

Though each technique is a groundbreaking achievement, there are a number of practical limitations to be overcome. The rate at which either gives entangled pairs is quite low. For heralded pair generation using a typical SPDC setup, the rate of three-photon events, from which you cleverly select a single pair, ranges from 0.001 to 0.1 Hz². Cranking up the pump laser power can give you more three-pair events, but then it will start to give you four-pair events as well, which will trigger your detectors and give a false-positive.

For the ELED, the Toshiba group showed an entangled pair rate of 3.0 Hz. This can be improved by increasing the coupling efficiency as well as increasing the injection current. Intrinsically, this device shows better promise as an ‘on-demand’ source since the probability of generating and entangled pair per voltage pulse is 3%³ - about 10,000 times more probable than generating a three-photon pair in SPDC⁴.

Both techniques show an entanglement fidelity of more than 80%. The primary reason that heralded generation using SPDC comes up short of perfect entanglement is due to the nonzero probability of the creation of simultaneous four-photon pairs. As mentioned above, four-photon events will also simultaneously trigger your detectors and give you a two-pair output instead of the single pair you expect. The imperfect entanglement in the ELED made by Toshiba primarily comes from unentangled background light from the surrounding diode structure. Eighty percent fidelity may not be useful for all quantum information protocols but is high enough for important components of quantum computing like teleportation and entanglement swapping³.

Finally, both techniques are not quite ready to be integrated on-chip. Walther et al.² made their pump source with a frequency doubled Ti:Sapphire laser Though Ti:Sapphs are the workhorses of ultrafast optics and are very robust (See earlier post for more details), they currently require a good amount of space on an optics table(roughly four feet long and 1 foot wide), expert knowledge of ultrafast optics to troubleshoot, and a good amount of money (~$100k). The ELED beats SPDC in this regard since it is compact and requires a simple low-voltage electrical pulse. Unfortunately, successful operation requires near-liquid helium temperatures. Salter et al.³ showed operation at a chilly 5 K.

Despite such hang-ups, one has to keep in mind the practicality of early computing and information processing. Could Mauchly and Eckert, the inventors of the ENIAC (which consumed 150 kW of power, used 18,000 vacuum tubes, and was so big that it needed to be housed in a 30 x 50 foot room) ever envisioned an iPod Touch? And even if the quantum version of the iPod Touch never materializes, perhaps this cool physics is just worth doing for its own sake.

References

1. C. Wagenknecht et al., "Experimental demonstration of a heralded entanglement source," Nature Photonics, 4, 549-552, (2010).

2. S. Barz et al., "Heralded generation of entangled photon pairs," Nature Photonics, 4, 553-556, (2010).

3. C. L. Salter et al., “An entangled-light-emitting diode,” Nature, 465, 594-597, (2010).

4. P. Kok, “Entangled photons report for duty,” Nature Photonics, 4, 504-505, (2010).

5. V. Zwiller, “A spooky light-emitting diode,” Nature Photonics, 4, 508-509, (2010).

6. P. Kok et al., “Linear optical quantum computing with photonic qubits,” Rev. Mod. Phys., 79, 135-174, (2007).

7. N. Gisin et al., “Quantum Cryptography,” Rev. Mod. Phys., 74, 145-195, (2002).

8. D. Dehlinger and W. M. Mitchell, “Entangled photons, nonlocality, and Bell inequalities in the undergraduate laboratory,” Am. J. Phys, 70, 903-910, (2002).

9. E. J. Galvez et al., “Interference with correlated photons: five quantum mechanics experiments for undergraduates,” Am. J. Phys, 73, 127-140, (2005).

10. J.J. Thorn et al., “Observing the quantum behavior of light in an undergraduate laboratory,” Am. J. Phys, 72, 1210-1219, (2004).

Erratum

2010-05-26T08:42:00.001-07:00

Greetings. If anyone is still paying attention, I wanted to clarify an error in post "Cutting-edge and Future Saturable Absorbers" originally posted on May 20. I was a little two-photon happy and incorrectly inserted a two-photon absorption process in the electron transition diagram. This has now been corrected. My apologies to author Amir Nevet for this mistake and many thanks to the author for clarifying the correct diagram of the second-order process. Best of luck to the authors developing this work. I know I am looking forward to the day when I can get my hands on a two-photon amplifier. If Nevet et al are taking pre-orders, I'd like mine fiber-coupled!

See you in Baltimore in 2011

2010-05-22T20:40:00.000-07:00

I hope all conference attendees, presenters, and organizers have made it safely back home by now. Thanks to all of you for your hard work, great research, and participation in our field. Though the economy has not been on our side, one wouldn't know it from the innovations demonstrated in both the academic sphere and marketplace at this conference.

I hope to see everyone at CLEO/QELS in Baltimore, May 1-6, 2011.

I would like to give special thanks to April Zack, head of OSA student chapters and the young professionals organization of the OSA, Dominique Smith, from OSA marketing communications, and Juliann Grant, OSA social media consultant, without whom this blog would not have happened.

Also, special thanks to Sam Rubin of Thorlabs for sending me home with enough Thorlabs T-shirts for everyone in my lab at Augustana, as well as the doggy bag of lab snacks which saved me one night at the hotel when I came down with a bad case of the munchies!

Most of all, thanks to all of you who took time to read the posts. I certainly benefited from writing them. Never would I have looked so carefully at what was available to me at the conference. I hope you came away with something as well.

Postdeadline Frenzy: Black is the new Black

2010-05-20T13:56:00.000-07:00

Get ready for the post deadline frenzy beginning at 8:00 pm this evening. Make sure to stretch and warm-up properly as you race from room to room. Some areas that caught my interest when browsing through the abstracts were new spectroscopic techniques, novel sources for trace gas detection and molecular fingerprinting, and how to make something really, really, black.

Many of us at CLEO are interested in building or using light sources, particularly lasers. After all, that's what the "L" stands for in CLEO. However, two papers in tonight's postdeadline session, CPDA5, "Coherent Perfect Absorbers: Time-reversed Laser," and CPDA6, "Darker than Black: radiation-absorbing metamaterials," address either destroying it or fully converting it into another form of energy. The former may be helpful for controlled optical energy transfer, and the latter for optimized energy harvesting in solar cells. Though physically different, both techniques utilize negative contributions of dielectric permittivity (one relies on a negative imaginary part and the other a negative real part).

If you are interested in light absorption, or cool optical analogs to astrophysics, you may also want to check out related work by Evgenii Narimanov, author of CPDA6, using metamaterials to create a propagation medium for EM fields analogous to the curved space-time near a black hole, in this case, an "optical black hole."

Cutting-edge and Future Saturable Absorbers

2010-05-20T10:50:00.000-07:00

Khanh Kieu, from University of Arizona, began his talk, CTuII2,"Generation of sub-20fs pulses from an all-fiber carbon nanotube mode-locked laser system" emphasizing the importance of saturable absorbers (SA) in mode-locked lasers. The SA is the device that is responsible for locking the modes in a laser cavity, thereby allowing the creation of pulses. Without one, you'd just have a continuous wave laser. In general, a saturable absorber is any device that transmits higher intensities of light at expense of lower intensities. They can be active, passive, real, or artificial. In ultrafast fiber-lasers, the typical SA of choice is a semiconductor saturable absorber mirror, SESAM, (a real SA relying on material response) or nonlinear polarization evolution, NPE, (an artificial one making use of polarization tricks). Kieu's point is that it makes sense to spend time developing the component of the mode-locked laser that is responsible for mode-locking.

Kieu and his collaborators at Arizona have been doing just that by developing SAs using carbon nanotubes. Though not the primary motivation, Amer Nevet, from Technion in Haifa, and his collaborators have also been developing effective SAs by showing the first example of two-photon gain in semiconductors, CKK1, "Direct Observation of Two-Photon Gain in Semiconductors."

From CLEO abstract CTuII2

Kieu's novel SA made from carbon nanotubes, packaged in a fused, fiber-coupler, has allowed him to make robust, few-cycle pulses in an all-fiber, ultra-compact footprint(see the Figure above from his Abstract). In fact, I have had some first-hand experience recently with building a similar oscillator. Using a fused carbon-nanotube SA from Kphotonics, a spin-off company started by Kieu, and approximately $500 of fiber components, it took only a couple hours of splicing for me to generate a self-starting 400 fs oscillator. It mode-locked the very first time I turned it on and requires no adjustment other turning up the pump power (truly turn-key). This is the easiest laser that I have ever built. Besides applications of this source for fiber-based frequency combs (CLEO talk CMX4) and super-continuum sources, Kieu is trying to market this laser for use in classroom demonstrations and teaching labs at the college level.

From CLEO abstract CTuKK1

The picture above shows the waveguide structure used by Amir Nevet and his collaborators to demonstrate two-photon gain. Two-photon gain is generated when a photon pair stimulates the emission of another identical photon pair in a second-order process (see schematic below). This means that gain is nonlinear, and now proportional to intensity. A pulse amplified in this way will experience larger gain at the peak and lower gain elsewhere. This has the same effect as a saturable absorber- even better, however, since the pulse experiences net gain rather than net loss. This technology holds great promise of changing typical means of pulse compression and mode-locking. The other great things about two-photon gain is it could be used for bi-stability and generating squeezed states of light.

Electron transition diagram of fully (doubly) stimulated two-photon emission

Expo, Idea Generation, and Multiphoton Microscopy

2010-05-19T10:45:00.000-07:00

Image from Webb Lab, Cornell University, Adapted by J. van Howe. Left: One photon fluorescence in a fluoroscein solution. Right: two-photon fluorescence in the same solution.

At the very first conference I attended as a new graduate student, I asked my advisor, "So what talks are you going to?" To my surprise he said, "Talks? I don't go to any talks, I catch up with my friends and colleagues and go to the expo to get ideas." My graduate advisor was exaggerating. He did, and still does, go to talks, but his advice then, which I still take to heart, made me realize how important it is to talk to colleagues after and in between talks, as well as the importance of the expo. From an academic point of view, the expo typically is a place to buy new tools to further on-going research. From from my graduate advisor's point-of-view it is also a place to find strengths and weakness in developing technology, the latter typically being more helpful for beginning new research.

As I was scouting companies to find out more information on Mid-IR laser sources (by the way IPG photonics and Daylight Solutions seem to be leading the market in sources in this spectral range), I learned about the impact multiphoton microscopy (MPM) has had on the sales of Ti:Sapph and OPO systems from Stephen Knapp of Coherent, Inc. In fact, there will be Market Focus talk, in the Biophotonics session on Thursday on the showroom floor from Arnd Krueger of Spectra Physics regarding this very subject. Also, be sure to check out an entire session devoted to MPM work, today at 1:30 pm in room A4, or check out the abstracts on the conference CD if you miss it.

A Ti:Sapph plus an OPO is not cheap. You're talking around $200k or more depending on options. These bulk solid state systems used to be the purview of only laser jocks. However, companies like Coherent and Spectra Physics are making them more into turn-key systems in order to put them into the hands (or onto the optical tables anyway) of biologists and biomedical researchers. Though companies like Coherent and Spectra Physics are leading the way of making these sources turn-key, the fact that they are still very expensive and fairly large makes us fiber laser specialists excited. We think the next generation of MPM sources will be all fiber-based and therefore truly compact, turn-key, and a fraction of the price.

To my surprise, Stephen told me that Coherent will sell up to 50 a quarter, mainly for use in MPM! So what is so great about MPM? Well, it is arguably the leading technique for deep-tissue imaging. Being in Chris Xu's group at Cornell University when I was a graduate student, who helped pioneer two-photon microscopy with Winfred Denk, and Watt Webb when he himself was a Cornell grad, MPM buzz has rubbed off on me and I can't miss an opportunity to say something about it. Particularly, I wanted to share one of my favorite photos taken in the Webb lab (above) that gets right to the essence of how MPM works.

The goal of MPM is to get rid of the scattering background outside of the focal plane, the photo on the left. These photons are noise and do not contribute to meaningful information about the sample. Using two-photon fluorescence, however, one gets photons mainly near the focal plane and nowhere else, thereby significantly reducing the background. This allows the biomedical researcher, or surgeon, to scan deep (~1 mm) through tissue. Reduction in scattering occurs because in the two-photon configuration, the probability of a fluorescence event is much greater at the focus of the objective than anywhere else.

The two-photon cross section of typical fluorophores is around 30 orders of magnitude smaller than the one-photon cross section. In order to get a two-photon event, photons must arrive "simultaneously." "Simultaneously" can be figured out from the Heisenberg uncertainty principle to be about 0.5 fs - just use the energy of the transition and solve for time. In order to get a two-photon event, one needs to bunch photons together to stack probability. The microscope objective does this in space and a pulsed excitation source does it in time. The focus is the most probable spot for excitation since photons are bunched in both space and time at this point and no where else. This is why you need a pulsed excitation source for MPM. For more details on MPM see the Dr. Bio webpage at Cornell.

Image from Webb lab and Nikitin lab at Cornell University. Left: H&E stained histology of sliced ovary. Right:Multiphoton image of a follicle within an unstained, intact ovary from mouse. Autofluorescence (green) derives from NAD(P)H and retinol within the tissue. SHG (red) delineates the bursa.

Above are some more pretty pictures of nonlinear microscopy in action. Note that on the left is a typical histology of a mouse ovary. The tissue has been excised, and then stained. On the right shows two-photon microscopy combined with second harmonic generation microscopy of an intact mouse ovary. The moral of the story is the one on the right required no cutting and therefore is much less invasive.

Tuesday is a Mega-day at CLEO

2010-05-18T08:00:00.000-07:00

All you have to do is flip to the schedule-at-a-glance in the conference program to see that today is a Mega-day or maybe I should say Tera-day at CLEO. Besides the technical program, the expo opens at 10:00 am, so does the history of the laser exhibit in the exhibition hall, the market focus presentations begin at 10:30 am, the welcome reception begins at 6:30 pm, and the day concludes with the Lasers Rock concert in the San Jose Civic auditorium (the Spanish mission-style building across from the convention center).

The line-up of the Lasers Rock concert is:

Phat Photonics, Oregon Health & Science Univ., USA
Eric Hansotte, Maskless Lithography, USA
Free Lunch Band, Lawrence Livermore Nat'l Lab, USA
Brian Kolner, Univ. of California Davis, USA
Bob Fisher, RA Fisher Associates, LLC., USA and Steven Block, Stanford Univ., USA
Yoshiaki Nakajima, Fukui Univ., Japan

Rumor has it that Steven Block is a capable bluegrass musician. I'm also particularly interested in hearing Brian Kolner who's fantastic 1994 review paper in J. Quant. Electronics, "Space-time duality and the Theory of Temporal Imaging" was the basis for much of my thesis work. Time-lens work appears in this conference in presentations CThBB7, JTuD57, and CThN5.

As I am trying to think of songs with references to lasers to request at the concert, I can only think of one, Killer from Queen, "Gunpowder, Gelatine, dynamite with a laser beam..." There must be more. Any help blogosphere?

Diagnosing Cancer with a Flashlight

2010-05-17T22:06:00.000-07:00

From Arjun G. Yodh, Biomedical Optics Group, University of Pennsylvania MRI axial slice, DOT axial slices of relative total hemoglobin concentration (rTHC), relative blood oxygen saturation (rStO2), relative tissue scattering (rSc), Optical Index, and a 3D image of region of interest are shown for malignant (left-side) and benign lesions (right-side). The black line indicates the tumor region.

I arrived at CLEO this afternoon bleary-eyed from a long plane ride and lack of sleep. However, three talks in CLEO Applications: Spectroscopy and Imaging held my attention firmly. What impressed me the most was how much information the particular researchers extracted from tissue or a tumor using what seemed like a small amount of data or rudimentary tools.

In presentation AMD4, Arjun Yodh, from University of Pennsylvania demonstrated the power of using highly scattered light from a tissue to not only reconstruct an image deep beneath the tissue surface (~ 1 cm), but to also gather functional information such as blood flow to and from a tumor. This technique, called diffuse optical tomography, relies on a diffusion model of photons through tissue, analogous to the diffusion of heat. In the figure above, Yodh and his collaborators could distinguish between malignant and benign breast tumors based on the functional information from diffuse scattering and absorption.

In presentation AMD1, Urs Utzinger from University of Arizona, showed fairly high specificity and selectivity in diagnosing ovarian cancer in post-menopausal patients by fluorescence signals, using UV-A to Near-IR excitation. Selectivity was accomplished by compiling and comparing excitation-emission matrices for malignant and benign tumors. Each value of an excitation-emission matrix is simply the intensity of the emission signal, where the rows of the matrix corresponds to the excitation wavelength and the column corresponds to the emission wavelength.

From SPIE,Response of cellular motility to the drug nocodazole. The initial state shows strong motility in the outer healthy shell, decreasing over approximately 1h as the microtubules are disassembled inside the cells. The bar is 100μm.

Finally, in presentation AMD3, David Nolte, of Purdue University showed that he could diagnose the effects of drugs on a tumor by how much it wiggled and shook- its motility, see the picture above. My favorite figure in his talk showed the frequency and strength of cell oscillations as a function of time after a drug or another kind of stimulus, such as heat, had been introduced. What part of the cell wiggled depended additionally on its health indicating motility can be used to label a cell's state.

Jury Duty and SERS Spectroscopy

2010-05-13T11:41:00.000-07:00

Schematic of SERS Technique from Kneipp et al Chem. Soc. Rev., 37, 1052–1060, (2008).

There has been a lag in my blog posting lately as I was recently performing my civic duty as juror in a narcotics case in my county for the last three days. Of course as a laser scientist my mind wandered from the case from time-to-time to the subject of how lasers could have been used to aid the investigation. After some browsing through databases, I found some studies using Raman Spectroscopy and surface-enhanced Raman spectroscopy (SERS) for identification of illegal drugs.

Though no CLEO papers directly address the spectroscopy of controlled substances, there are 65 CLEO papers devoted to applications of Raman scattering, 113 on laser spectroscopy, and an entire session devoted to SERS and applications of Raman scattering, CFA. Surface-Enhanced and Fiber Raman Technologies, on Friday May 21.

SERS and SERS-related techniques have particularly been exploited in biomedical spectroscopy in recent years. Three papers in Friday's session use SERS specifically for biomedical applications. CAF2 exploits SERS to analyze DNA, CAF4 demonstrates SERS through fiber and with a more standard biological imaging wavelength of 800 nm, and CAF6 uses SERS to perform spectroscopy on human skin.

For those who don't know or need refreshing, a Raman spectrum gives information of the characteristic vibration of molecule, a "vibrational fingerprint". Raman cross sections are typically orders of magnitudes weaker than those from fluorescence spectroscopy. By introducing metal nanostructures into a solution of molecules to be probed, a cell, or tissue, one can greatly enhance the Raman signal due to interactions of the opitcal field with surface plasmons. Check out a nice review paper from the Kneipp's for more background, Chem. Soc. Rev., 37, 1052–1060, (2008).

Conference R&R: Exploring San Jose

2010-05-04T20:11:00.000-07:00

Falafel's Drive-in, Photo from Gena S. from Yelp.com

This will just be my second visit to San Jose. Last time was for CLEO 2007 and I pretty much didn't leave the downtown area (just ping-ponged back-and-forth from the convention center to my hotel). For this visit, I'm interested in taking some time to explore what the city has to offer when there is some conference down-time. My hope is that any blog followers with more experience in Northern California, or who are native to the area, will help point us tourists in the right direction. So please comment!

My first assumption is that most of us will not have a car. So my recommendations from surface web-browsing of area attractions and restaurants will be contingent upon reasonable trip-time using public transportation or walking.

The Winchester Mystery House and Restaurants along the way:

Is it a freak of architecture, a wonder, or just plain bizarre? The last time I went to San Jose, a colleague recommended that I visit The Winchester Mansion . I never did, but will be going this time. One legend has it that after the premature deaths of both her daughter and husband, Sarah Winchester, heiress to the Winchester rifle fortune, sought advice from a medium in Boston, MA. The medium told her that her misfortunes were due to the spirits of American Indians, Civil War soldiers and others killed by Winchester rifles. To appease the spirits she was to move West and build a home for them and never cease construction. The mansion, whose rooms were continually added and remodeled until Sarah's death is a labyrinth of winding corridors, stairs that descend and then ascend before they reach their destination, doors that open to blank walls, and other oddities. A tour of the mansion costs $28. From the convention center take Bus 23 to the Winchester Shopping Center from which you can walk the rest of the way. Travel time is about 45 minutes.

Some searching on tripadvisor highlighted some restaurants along or near Bus Route 23. The most popular on tripadvisor was Falafel's Drive-in at 2301 Steven's Creek Blvd, which offers African, Mediterranean, Middle-Eastern cuisine. And hamburgers of course! Take Bus 23 to San Carlos and Topeka and then walk west rest of the way- San Carlos Blvd. becomes Steven's Creek Blvd. Total travel-time 24 minutes. Another restaurant in this area slated for good Indian cuisine is Amber India in Santana Row. This time, take Bus 23 from the convention center to Valley Fair Shopping Center, then walk south the rest of the way to Santana Row Shopping Center. Total trip-time 40 minutes. Another recommended restaurant in Santana Row is Thea, which serves Turkish and Greek food.

Other Recommended Restaurants:

If you want to see belly dancing while enjoying Moroccan cuisine, take the light rail north to the Gish stop. The Moroccan Restaurant Menara is located at 41 E. Gish. Travel-time is a short 11 minutes.

La Victoria, immediately next to the convention center on San Carlos, was ranked third on tripadvisor. The cuisine is Californian/Mexican. In the comments, many customers raved about the orange sauce which they sell in bottles if you want to take some home.

Green Space and Exercising:

Though I don't run as often as I should, this is one of the ways I try to stay in shape. It is also a nice way to explore a city. Unfortunately, San Jose seems to be a lot of highway and concrete, but it looks like are at least a couple of parks fairly easy to get to from the convention center. What looked most promising to me was to take the light rail to the Penitencia Creek stop and then follow Penitencia Creek Rd northeast toward Alum Rock Park. It is just 2.5 miles along Penitencia Creek Rd to the base of the Park. Along the way you can leave the road and run through Penitencia Creek County Park which connects to Penitencia Creek Trail. If you are a runner you may already know about mapmyrun.com, which gives you suggested routes and mileage from local runners. Just make sure you give your Falafel plenty of time to digest before running up Alum Rock.

Pre-Conference Homework

2010-04-25T21:40:00.000-07:00

I am a bit ashamed to admit it, but this is really the first time that I have done any pre-conference homework. What I am referring to is looking at the conference schedule, browsing the website, looking through abstracts, and even using the online planner to make an itinerary.

Though maybe a bit nerdy, or perhaps just naive, this has been an epiphany for me. For any conference-goers reading these posts, if you don't already, I urge you to take a look at the conference program well before you get to San Jose. Do a little planning now so that you can arm yourself with those good questions to advance and broaden your research. Some brief searching on the CLEO website last night already got me thinking about some new directions for MID-IR work as well as resurrecting some old ideas I had about novel pulsed sources using optical-phase locking.

To start your planning, I suggest going to the Hot Topics categories midway down on the main conference page. Typically I am cynical about what seem like cute little multimedia ploys to spice-up dry, technical subject-matter like the You Tube shorts on this page. However, these are well delivered and helpful. They are worth a listen. I found myself playing them all even though many were out of my sub-field. The list of tutorials and invited talks beside each short was particularly useful.

In one of the shorts (above), Peter Smowton, the Semiconductors Subcommittee Chair, from Cardiff University teased my interest in prompting what he thinks could be a "controversial" talk, CTuKK1, "Direct Observation of Two-Photon Gain in Semiconductors." This is the first observation of two-photon gain in a solid. Be sure to show up at 4:45 pm on Tuesday, May 18, in room A6 to watch the drama unfold.

In another short, Konstantin Vodopyanof, the General Chair from Stanford and Brian Applegate, the Biophotonics Subcommittee Chair, from Texas A&M University prompted me to schedule William Moerner's tutorial on supper-resolution into my itinerary, 4:45 on Thursday, May 20, in room A4. What is super you may ask? Less than 100 nm. Impressive.

After browsing Hot Topics, you may try what I did and build up a conference itinerary.

If you are going to CLEO you're a nerd already, embrace it and do some nerdy planning too.

Missing Optics and Volcanic Lightning

2010-04-20T11:25:00.000-07:00

Photo from Marco Fulle, National Geographic Daily News

In the lead-up to CLEO I have been trying to do some work in the MID-IR wavelength range. I have been waiting for some CaF2 lenses that were due to arrive a few days ago only to find that they were held up by the ash plume from Eyjafjallajokull's recent eruptions. It turns out that the distribution center from where my lenses were to be shipped is in Germany.

Searching the news for more information, I learned about the woes of poor stranded European travelers (rock stars, film-makers and pro-wrestlers included; it seems ash plumes don't discriminate),how to pronounce the name of the Icelandic volcano that caused all of this trouble (by the way it is EY-ya-fyat-lah-YOH-kuht), debate among officials about the safety of flying through ash plumes, but most interesting to the scientist in me, volcanic lightning.

I stumbled across these stunning pictures on the NY Times blog Lens from Icelandic photographer Ragnar Th. Sigurdsson. These photos that show the explosions, ash, and volcanic lightning from Eyjafjallajokull seem to be more like something from a George Lucas film (like that fiery lava planet in Star Wars: Episode III) than reality.

I then did some browsing on volcanic lightning to find some more photos and some explanation . The same ingredients in the eruption are found in thunderstorms: water droplets, ice, and particles all interacting. The ash plume provides lots of surface area for charging. I am reminded of stories I've read about the dust bowl in the plains of the U.S. during the 1930s when people refused to shake hands for fear of large static shock and that they also dragged chains from the tailgates of their cars to ground charge build-up. I guess it should be a no-brainer that lots of moving dust = lots of static build up.

I wish those still delayed in Western Europe safe and uninterrupted travel. May your delays be short. Maybe my lenses will arrive soon too...