CLEO:2011 Shows Off Applications and Opportunities

5. May 2011

By Patricia Daukantas

The weather outside the Baltimore (U.S.A.) Convention Center has been varying wildly, from warm and summery to cool and rainy. Indoors, however, the atmosphere of the CLEO:2011 conference was steadily abuzz with exciting applications of the latest photonics technologies.

Ultraviolet LEDs Can Disinfect Water

Although CLEO is primarily a laser conference, some tracks focused on other photonics technologies, such as photovoltaics and quantum computing. Following a joint symposium on semiconductor ultraviolet (UV) lasers and LEDs, a session reviewed several practical applications of UV LEDs.

One task for which these devices are particularly suited is the removal of harmful germs and other contaminants from drinking water. Gordon Knight, a research manager at Trojan Technologies (Canada), explained that UV light penetrates the cell membranes of bacteria, viruses and protozoa and permanently alters their DNA so the critters can’t reproduce and infect humans. UV rays can also break down organic contaminant molecules, as long as the molecular absorption spectrum matches the output of the UV sources.

Water treatment specialists are primarily interested in the UV-C spectrum (200 to 280 nm), in which the peak absorption spectrum of germ DNA falls, Knight said. The industry’s workhorse has been the low-pressure mercury arc lamp, which has a strong emission peak at 254 nm. However, solid-state UV sources could be more energy-efficient and could maintain their steady output for five times longer than the mercury lamps.

Although some technical challenges remain in the development of UV-C LEDs--namely, cost and the need to boost individual chip output above 5 mW--Knight is confident that these sources will provide efficient instant-on operation for future water treatment devices, both in municipal plants and perhaps even in household-sized systems.

IARPA: An Opportunity, Not a Misspelling

You’ve heard of DARPA, but what about IARPA? The Intelligence Advanced Research Projects Agency, a new branch of the U.S. government’s spy agencies, recently started searching for “high-risk, high-payoff” research programs to boost America’s intelligence-gathering efforts.

According to IARPA official Michael C. King, the agency is especially interested in significant advances in techniques to gather biometric data from distant, moving human subjects. Successful proposals require not just a good idea, but also a capable leader to guide the research project. One U.S. team followed King’s talk with a discussion of their own technique for so-called “standoff biometric identification” of people. According to Brian C. Redman of Lockheed Martin (U.S.A.), Fourier transform profilometry involves bouncing fringes from an 808-nm laser off the subject, capturing it and its two-dimensional fast Fourier transform, then doing an inverse transform and merging it with the original data. The laser pulses are eye-safe and, with a duration of 100 microseconds, short enough to freeze motion at a brisk walking speed of 1.5 m/s. The near-infrared light can even “see” through most sunglasses, Redman said.

Applied optics, Biomedical optics, CLEO/QELS, Energy, Lasers, Lasers, CLEO, OSA, Photovoltaics , , , , , ,

CLEO:2011--Two Compelling Technological Histories

3. May 2011

By Patricia Daukantas

Every scientific advancement has a story behind it. Telecommunications fibers and optical coherence tomography (OCT) are no different. Donald Keck and James Fujimoto--the first two CLEO:2011 plenary speakers--did a great job of telling those true tales.

Donald Keck, a retired Corning Inc. (U.S.A.) scientist who participated in the development of the first low-loss optical fiber, attributed the telecom boom to a “syzygy” of rapid-fire technological developments four decades ago. In addition to that first practical fiber, the earliest computer-network experiments, the room-temperature laser chip and the computer chip all appeared between 1969 and 1971.

Evoking the original notion of the laser as a “solution looking for a problem,” Keck drew chuckles by reminding the audience of schemes for laser cutting of trees, laser-made nipples for baby bottles and Arthur Schawlow’s “laser eraser” for typists. Early proposals for laser telecommunications--by sending light beams down 2-in.-wide coaxial cables--were not much more practical.

Fortunately, British government researchers asked Corning for help in creating glass fibers with attenuation below 20 dB/km, at a time (1966) when the best silica fiber suffered from signal loss of 1,000 dB/km. Drawing upon glass research from the 1930s to the 1950s, Keck and his Corning colleagues started tracking down and eliminating the sources of optical loss in fiber.

Their initial fiber-drawing equipment was crude--including a household vacuum cleaner--but effective. When Keck tested the first fiber with a loss of only 17 dB/km, he was so impressed that he wrote in his lab notebook, “Whoopee!” However, in 1970 an Applied Physics Letters reviewer initially rejected the Corning team’s paper because, Keck said, “it lacked believability.”

Today’s single-mode fibers fulfill Keck’s 1972 prediction of operation with losses of 0.2 dB/km or less at the 1,550-nm wavelength. Progress in telecommunications has come rapidly, especially after the 1984 court-ordered breakup of the old Bell-System AT&T, which created “a lot of fiber-hungry ‘baby Bells,’” Keck said. With the development of fiber that can bend around sharper corners without introducing losses, the industry is poised to use fiber in ways traditionally associated with copper wire.

OCT: Joining Optics and Clinical Science

OCT is a method of imaging using echoes of light--the optical analogue of ultrasound, said James Fujimoto of the Massachusetts Institute of Technology (U.S.A.). In terms of resolution and tissue penetration, OCT bridges the gap between ultrasound and confocal microscopy.

Although Michel A. Duguay and A.T. Mattick first suggested the technique in a 1971 Applied Optics article, the first demonstration of OCT, performed on a cadaver eye, was published two decades later, according to Fujimoto. Since then, progress has come rapidly, with the technique’s extension to living tissue and the commercial development of OCT equipment for clinical use. Today, spectral domain interferometric techniques have improved both the speed and sensitivity of OCT. High-speed CCD cameras and volumetric data-rendering techniques have added to OCT’s ability to track dynamic processes such as capillary blood flow.

OCT is now moving beyond ophthalmic procedures into the world of intravascular imaging, where the technique can identify unstable arterial plaques and guide the medical treatment of those dangerous blood-flow blockers.

Fujimoto said that there has been a huge increase in intravascular OCT procedures in the last three years. The development of tiny fiber-optic catheters and the Fourier-domain mode-locked (FDML) laser have helped make this possible.

Finally, Fujimoto drew the audience’s attention to one of this CLEO’s postdeadline papers, which reports a record imaging speed for OCT using a swept single-mode vertical-cavity surface-emitting laser (VCSEL). OCT promises to be an exciting technological field to watch in the near future.

Applied optics, Biomedical optics, CLEO/QELS, Fiber optics, Lasers, Lasers, CLEO , , , , , , , , , , , ,

CLEO:2011 Opens with Strong Technical Sessions

3. May 2011

By Patricia Daukantas

CLEO:2011, the annual laser conference organized by OSA and other scientific societies, got off to a strong start today with a full range of sessions on pure laser physics and applications of the technology. Here are a few highlights from Monday‘s sessions:

  • Could lasers make your automobile burn gasoline more efficiently than spark plugs do? Researchers from Japan and Romania have developed all-ceramic micro-lasers that could zap the insides of car-engine cylinders with multiple sub-nanosecond pulses to ignite a lean mixture of fuel and air. The speaker for the group, Takumori Taira of Japan’s Institute for Molecular Science, declined to predict when laser-powered cars will hit the market. The team’s research has been getting a lot of press, including a mention by a New York Times blogger.
  • Although General Electric Corp. may be more famous for manufacturing light bulbs, appliances and jet engines, the company has made several important contributions to laser technology. In his talk on laser materials processing, Marshall G. Jones of GE Global Research (Niskayuna, N.Y., U.S.A.) recalled that Robert N. Hall of GE invented the semiconductor injection laser--forerunner of the innards of all laser printers and CD players--and Joseph P. Chernoch devised the face-pumped laser in 1972. Today, GE is more concerned with laser drilling, welding and cladding techniques for manufacturing components of locomotives and turbines. Its scientists are developing fiber lasers that meld the high stability of Nd:YAG lasers with the high efficiency and sharp focusing ability of CO2 lasers.
  • It’s taking awhile, but eventually the European Space Agency will launch Aeolus, a wind-lidar satellite containing the first ultraviolet laser to fly in space. Dutch physicist Martin Endemann explained that the transmitter assembly for the 355-nm laser must last for 5 billion shots over 39 months in orbit without significant degradation or coating damage. His team found that the system needed to contain low levels (0.2 mbar) of oxygen in order to keep the UV optical components from darkening. The laser should be ready to be installed in the satellite next year, pending a successful extended vacuum-chamber test this fall.

Tonight is the first of two plenary CLEO plenary sessions, this one featuring Donald Keck and James Fujimoto, both highlighted in OPN for May 2011, along with their fellow plenary speakers Moti Segev and Susumu Noda.

CLEO/QELS, Lasers, Lasers, CLEO , , , , , , ,

Navigating the Laser Maze at FiO/LS

27. October 2010

By Patricia Daukantas, OPN Contributing Writer

LaserFest--the yearlong celebration of the 50th anniversary of the first laser--is not over yet. At this year’s FiO/LS meeting, LaserFest has a strong presence in the exhibit hall.

Since arriving in Rochester (N.Y., U.S.A.), I’ve been hearing a lot about the Laser Maze, so by the time the exhibit hall opened yesterday morning, I could hardly wait to try it. The University of Rochester’s student chapter of OSA developed the maze with a grant from the LaserFest program. Previously the students had set it up at the Rochester Museum and Science Center, but they moved it over to the OSA meeting for the enjoyment of attendees.

The premise of the Laser Maze will be familiar to anyone who has ever seen one of those bank-robbery or jewel-heist movies. A laser and a light sensor make up part of a complete circuit. Interrupt the laser beam and the circuit breaks.

In this case, the circuit was powering a small music player, so breaking the beam stopped the music (instead of setting off an alarm like in the movies). The laser beam bounced side to side several times off parallel mirrors close to the floor, so the maze walker had to step through the gaps between the reflected beams.

Of course, in the movies the audience sees the laser beams from the side, thanks to either smoke or computer-generated effects. No such luck with the Laser Maze, however. The LaserFest people had a small theatrical “smoke” machine, but due to a combination of the bright ceiling lights and the ventilation in the exhibit hall, the particles did not linger long in the air. Thus, the maze walker had to look for tiny red dots on the mirrors and imagine where the beam might have gone, based on equal angles of incidence and reflection.

Since I didn’t want to embarrass anyone else, I had someone take photos of me trying to step through the maze.Here I’m starting off on the right foot.



I’m home safe after figuring out the first beam path.



Another step, probably higher than it needs to be.



Do I still have what it takes?


Dang! I just nicked that last horizontal beam!


To make the maze even more challenging, the Rochester chapter set up a second set of reflecting beams and mirrors … vertically. Technically, to complete the maze, one had to get through both the horizontal and vertical sections without interrupting the recorded music. However, I probably would have had to slide myself on the floor to get through that maze, and I wasn’t feeling quite that acrobatic.

OSA Student Chapter Competition 2010

At last year’s FiO/LS, OSA student chapters built miniature solar-powered cars and raced them. This year, they were given a different challenge: to create an educational tabletop exhibit to teach young people about one or more principles of optics.

Yesterday I visited several of the chapters’ tables, but since the competition is continuing into today, I’ll write up more details for tomorrow’s blog entry.





Frontiers in Optics, Laserfest, Lasers, Optics and pop culture, Photography , , , , , , , , , , , , ,

FiO/LS Day One: From Spooky Entanglements to Space Lidar

26. October 2010

By Patricia Daukantas

Halloween is the season of ghosts, goblins and vampires … so why not add some spooky quantum entanglements to the mix? On a cloudy, damp morning in Rochester (N.Y., U.S.A.), the plenary speakers at OSA’s 94th annual meeting, Frontiers in Optics, took the audience on a tour of Bell inequalities, wild biomolecules and other scientific treats.

This year’s Ives Medalist, OSA 2007 President Joe Eberly, used elementary trigonometric identities (remember those?) to demonstrate a seeming contradiction in a thought experiment about a polarizing interferometer. Eberly, a longtime professor at the University of Rochester, solved the conundrum by showing that the photons were entangled in what is now known as a Bell state.

Measuring degrees of photon entanglement is one of Eberly’s recent interests. He noted that Erwin Schrödinger introduced the notion of entanglement in 1935 -- and, 75 years later, scientists still don’t have a lot of quantitative answers about it. This is “a guarantee of permanent employment for a physicist,” he said, generating a ripple of chuckles among the audience.

One of the two winners of the American Physical Society’s Arthur M. Schawlow Prize, Henry Kapteyn of JILA (University of Colorado, U.S.A.), paid homage to the award’s namesake. “It was clear he liked to point lasers at things and blow them up, and that’s mostly what we do,” he said. Fortunately, most of the high-energy (and soft-X-ray) lasers he talked about haven’t exploded, and he predicted that there are excellent prospects for generating hard X-ray laser beams from tabletop devices in the near future. His wife and co-prize-winner, Margaret Murnane of JILA, will speak at tonight’s APS Laser Science banquet.

Plenary speaker Steven Block, a professor of physics and biology at Stanford University (U.S.A.), took the audience on a tour of “riboswitches,” non-coding messenger RNA strands that control gene expression by changing their structure when they selectively bind to a signal molecule. In evolutionary terms, this is probably the earliest form of molecular control at the cellular level, but it was poorly understood until scientists could start manipulating the molecules with optical tweezers. (Attendees of CLEO/QELS 2010 in May might remember Block’s blues mandolin performance.)

The final plenary speaker, Alain Aspect of the Institut d’Optique (France), gave a history lesson on the Hanbury Brown and Twiss interferometry experiment of the mid-1950s and its relevance to modern-day quantum optics.

Checking the Efficacy of Breast-Cancer Therapy

Can oncologists deduce the efficacy of breast-cancer treatment as early as one day after the start of chemotherapy? According to Albert Cerussi of the Beckman Laser Institute (U.S.A.), this can happen, thanks to a technique called diffuse optical spectroscopic imaging (DOSI).

Traditional “adjuvant therapy” for breast cancer calls for surgery first, followed by a round of chemotherapy. Oncologists are now moving to “neo-adjuvant therapy,” in which the chemo comes first -- making it even more important to monitor the patient’s response to the powerful drugs.

DOSI works in the near-infrared window of 650 to 1,000 nm; those wavelengths penetrate tissue relatively well, although the photons take a “random walk” through the tissue (hence the “diffuse” part of the imaging). Instead of getting the black-and-white patterns of a traditional mammogram, DOSI provides spectral information about tumor biomarkers such as oxygenated and deoxygenated hemoglobin.

Researchers first studied DOSI at the midpoint of chemotherapy, when oncologists usually assess the patient and decide whether to switch therapies. But the researchers from Beckman and the Chao Family Comprehensive Cancer Center (both part of the University of California at Irvine) found that they could detect changes in the biomarkers one week and even one day after the start of chemotherapy.

According to Cerussi, scientists are even studying whether the technique could predict whether chemo will help a particular patient even before the treatment starts, but they are still trying to understand the biological process behind that. In the near future, researchers will look for additional biomarkers, shrink the size of the equipment, and join a clinical trial involving four other cancer centers.

(Note to readers of OPN’s Twitter feed, @OPNmagazine: Cerussi’s talk was the one I chose out of eight simultaneous invited talks at the start of the afternoon sessions. It was a tough call -- the other topics included luminescent solar concentrators, laser refractive surgery for cataracts and long-term monitoring of buried fiber-optic cables.)

Industrial Physics Forum

This event, sponsored by the Corporate Associates of both OSA and the American Institute of Physics, drew large crowds to several talks -- particularly the one by quantum cascade laser pioneer Federico Capasso of Harvard University. On Monday, the forum covered a range of biomedical and environmental applications of lasers.

An Earth-observing lidar satellite called CALIPSO (for “Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations”) has been in orbit since April 2006, and Carl Weimer (Ball Aerospace, U.S.A.) reviewed its ongoing engineering and science results.

As I described in an OPN article last year, CALIPSO is part of an “A-Train” of environmental satellites in the same orbit, with roughly 15 minutes of spacing between them. Its dual-wavelength (532 and 1,064 nm) lasers collect data in a 70-m-wide “curtain” from ground level to about 40 km altitude.

So far, the satellite has collected 6.6 terabytes of data from 2.6 billion laser shots, Weimer said. Its estimated particle sizes within cloud distributions provide important input for scientists’ models of global atmospheric circulation.

The Industrial Physics Forum is concluding this morning with sessions on lasers’ applications in metrology and other “frontiers of physics” areas.

The Day Ahead: Tuesday

This afternoon, brand-new OSA Honorary Member Arthur Ashkin will speak first at a symposium honoring his pioneering work with optical tweezers. The FiO/LS exhibit hall will open, and OSA student chapters will kick off their lesson plan competition. Two other events of particular interest to young professionals are a public-policy forum and the Minorities and Women in OSA (MWOSA) tea. Finally, we’ll all learn who won the OSA officer elections for 2011.

2010-10 October, Applied optics, Biomedical optics, FiO/LS, Lasers , , , , , , , , ,

Another OSA Member Wins MacArthur ‘Genius Grant’

29. September 2010

By Patricia Daukantas


Whoops – yesterday I forgot to note that a second OSA member is among the 23 winners of the annual “genius grant” from the John D. and Catherine T. MacArthur Foundation.


OSA member Nergis Mavalvala, a physics professor at the Massachusetts Institute of Technology (U.S.A.), has done significant research at the intersection of optics, quantum physics and gravity. MacArthur Fellows receive $500,000 over five years with no strings attached.


When Mavalvala, now 42, was still a graduate student, she developed a prototype laser interferometer for detecting gravity waves. The principles of that instrument were later incorporated into the Laser Interferometer Gravitational-Wave Observatory (LIGO).


The MacArthur Foundation has put a brief biography and video of Mavalvala online. OPN published more information on LIGO in the May 2008 issue and the July 1995 issue.

2010-09 September, Applied optics, Astrophysics, Lasers , , , ,

AFOSR LaserFest Event Highlights Work of OSA Fellows

11. August 2010

By Christina Folz, OPN Managing Editor

On August 6, the Air Force Office of Scientific Research (AFOSR) continued the 2010 LaserFest celebration with its own event highlighting everyone's favorite technology this year. The event showcased the work of three OSA Fellows--Alan Willner, who works on optical communications at the University of Southern California; Margaret Murnane, who is studying high-peak-power physics with lasers at the University of Colorado, and Richard Miles, a Princeton professor who spoke about the role of lasers in aerospace. Two other laser experts--Robert Jones and Gary Teraney--described the important role that lasers are playing in the defense industry and in medicine. Each of the participants had been funded by AFOSR as grad students and went on to become distinguished leaders in the laser field.

For those who missed the event, or who simply sought more info, yesterday the AFOSR held a "bloggers roundtable" moderated by Howard Schlossberg, the program manager at AFOSR, to discuss the event and answer additional questions about the state-of-the art in laser technology. Schlossberg was joined by several of the event participants, including Willner and Miles.

And for those who missed THAT (including this humble blogger), you're in luck: A podcast and transcript of the roundtable are posted on the Department of Defense's blog

Schlossberg emphasized the importance of solid-state lasers in particular as pivotal to modern laser research and technology. "The primary emphasis by us and by others as well is in solid-state lasers, either on bulk solids, slabs pumped with semi-conducted lasers, or in optical fiber lasers," he said. He also called medical and materials processing two of the biggest application areas of lasers these days.

And don't worry--LaserFest is far from over. "At meetings, they'll have demonstrations and displays," Schlossberg said. "If you get on the LaserFest website, you'll see some of the terrific movies of early times." 

Party on!  

2010-08 August, Applied optics, Laserfest, Lasers, Optics history , , , , , , , ,

Lasers Widen Telescopes’ Clear Field of View

6. August 2010

By Patricia Daukantas


For the past decade, astronomers have used laser guide star (LGS) adaptive-optics systems to remove the blurring caused by atmospheric turbulence above ground-based telescopes. Such systems, however, have always faced one restriction: an extremely narrow field of sharp viewing.


A team from the University of Arizona (Tucson, U.S.A.) has managed to widen that sharp field by developing a five-laser guiding system for the MMT telescope on Mount Hopkins in southern Arizona. The astronomers report on their system in the August 5 issue of Nature.


Michael Hart, of the university’s Steward Observatory, and colleagues wanted to study aging star clusters at near-infrared wavelengths (1.25 to 2.2 μm). One such cluster, dubbed M3, nearly fills the 110-arcsecond-wide field of the MMT’s infrared camera.


The researchers arranged five 4-W, 532-nm pulsed lasers in a pentagon and projected them from a small telescope behind the MMT’s adaptive secondary mirror. A combination of three sensors detects the aberrations in the Rayleigh-backscattered light coming back to the telescope, estimates the aberration from ground-level turbulence and directs the secondary mirror to correct the aberrations.


On a night when the native “seeing,” or point-spread-function diameter of stellar images, at the MMT was only 0.7 arcseconds, the astronomers improved it to 0.3 arcseconds over a 2-arcminute-wide field of view – roughly the same as the Hubble Space Telescope gets with its most recent upgrades, but with a bigger aperture to gather more light.


Astronomers are now developing a similar system for the Large Binocular Telescope on Arizona’s Mount Graham.

2010-08 August, Astronomy, Lasers , , ,

Happy (Belated) 95th Birthday, Charles Townes!

5. August 2010

By Patricia Daukantas


Last week, Charles H. Townes passed yet another milestone: he turned 95 years old.


Townes, now of the University of California at Berkeley (U.S.A.), is of course most famous in the optics community for his fundamental contributions to laser theory:


  • The development of the first maser with James Gordon and Herbert Zeiger in 1953, as Gordon recounted in a recent OPN feature article; and
  • The principles behind the optical maser, or laser, published by Townes and his brother-in-law, Arthur Schawlow, in December 1958.

Along the way, he’s worked at Bell Labs and three prominent universities, served on various U.S. government committees and think tanks, held a Guggenheim Fellowship and a Fulbright Scholarship, and won the Templeton Prize for contributing to the understanding of religion.


As we’ve noted in past OPN blog posts, Townes is still active in astrophysical research. So far in 2010, he and his colleagues have published two articles relating to Berkeley’s Infrared Spatial Interferometer, a three-telescope system with high spectral resolution. This year, which is the 50th anniversary of the first working laser, he’s been invited to speak at many scientific conferences, including a special historical symposium at CLEO/QELS 2010.


We should also note that 2010 marks two other milestones for Townes. It was 40 years ago, in 1970, that Townes was named an OSA Honorary Member. And it was 50 years ago that Townes, along with 14 other physicists, chemists, engineers and physicians, was named a representative of “U.S. Scientists” for Time magazine’s 1960 “Men of the Year” (now "Person of the Year") issue. Townes and bubble-chamber inventor Donald A. Glaser are the two surviving members of that august ensemble.


Townes and his wife of 69 years, Frances, have four daughters. We wish him a Happy Belated Birthday and much joy with his family.

2010-08 August, Astronomy, Astrophysics, Lasers, Optics history , , , ,

CLEO: The Wrapup

29. May 2010

By Patricia Daukantas


To wind up OPN’s coverage of CLEO/QELS 2010, I would like to spotlight some of the interesting things that I didn’t get a chance to write about during the conference.


Weather Guy to Lidar Specialists: Please Help


A meteorologist at California State University at Chico (U.S.A.) presented a list of opportunities for lidar researchers to help improve his group’s technology for studying atmospheric aerosols.


Shane D. Mayor uses a direct-detection infrared lidar instrument dubbed REAL (for Raman-shifted Eye-safe Aerosol Lidar) to study how particulate matter moves with air currents. He has participated in several simulations of bacterial agent plumes – this knowledge could be important in the case of a biological weapons attack.


REAL operates at 1,543 nm, which Mayor said is in the “sweet spot” between shorter-wavelength retinal hazards and insufficient detector performance above 2 µm. The 1.5-µm zone also offers such desirable qualities as low molecular scattering, low background radiation from the sky, and compatibility with telecom components. Mayor and a colleague designed a Raman shifter for converting the REAL Nd:YAG laser output from 1,064 nm to 1,543 nm (Appl. Opt. 46, 2990).


Unfortunately, the flashlamps on REAL’s pump laser need replacement every 20 million shots or 23 days – at $200 each, that amounts to $6,350 per year, Mayor noted. Also, the CSU-Chico lidar setup requires a tractor-trailer for transportation, but Mayor’s goal is to shrink that down to fit in a more mobile van.


Mayor listed a number of ways that optical scientists could help improve REAL. They include:


  • Reduce or eliminate flashlamp replacement.
  • Increase efficiency by reducing power consumption and waste heat.
  • Further reduce the mass of the beam steering unit mirrors, which are now 14 kg each.
  • Develop a high-precision pulse energy monitor that can measure shots to ± 1 percent.
  • Figure out how to monitor beam divergence continuously on the fly.


What Makes Counterfeit Money Funny?


Can measuring the intrinsic fluorescence lifetime of U.S. paper money distinguish between phony bills and the real thing? Researchers from Yale University (U.S.A.) believe that this technique could be used for forensic identification of counterfeit money.


The key, according to biomedical engineers Michael J. Levene and Thomas Chia, is that the paper for all U.S. currency comes from a single source. Although the exact “recipe” for that paper is secret, it has a very consistent fluorescence lifetime “signature” that differs from that of other types of papers made from wood, cotton and linen pulp. U.S. currency ink is essentially non-fluorescent, although the serial numbers on bills scatter light. (Inks on some non-U.S. currency, like the Mexican 100-peso note, do fluoresce, so that could be important in detecting foreign fakes.)


The researchers used a custom-built two-photon microscope, with an excitation wavelength of 735 nm, to study U.S. currency – mostly $100 banknotes, since they are the highest-valued bills targeted by counterfeiters. (They also tested some lower denominations as a control group.) They also tested three kinds of counterfeit bills provided to them by investigators: digital scans onto printer paper, counterfeit bills printed on cotton-linen-blend paper, and so-called “bleached” low-denomination bills that were illicitly reprinted with a higher denomination.


Levene and Chia didn’t know the exact provenance of the counterfeit money. “They [investigators] don’t like us to hold onto the bills for more than a few hours and won’t tell us much about where they came from, and we’re not going to make our own,” Levene said.


All the genuine currency notes had consistent short- and long-lifetime components to their fluorescence. The printer-paper fakes had only the longer-lifetime component. Other counterfeit bills had noticeably shorter long-lifetime components.


The testing group included bills dating back to the 1970s, and because the United States has been using the same paper supplier for so many decades, the two-component intrinsic fluorescence lifetime signature is “remarkably consistent” over the years, Levene said.


Small and Big Lasers


Qi Qin of the Massachusetts Institute of Technology (U.S.A.) and colleagues at two other labs built a tunable terahertz “wire laser” whose cavity is much narrower than its operating wavelength. The researchers tuned the laser by moving either a metal or dielectric “plunger” outside the laser cavity. (The gold plunger shifted the wavelength shorter and the silicon plunger made the operating wavelength longer.)


The group’s first design, as reported in the original CLEO proceedings, achieved 137 GHz of tuning centered on 3.8 THz. To get rid of the static friction that made the plunger stick and jump, they designed a MEMS-type plunger made up of layers of gold, silicon and silicon dioxide. The revised laser, only 10.5 µm wide, registered a total shift of 330 GHz between 3.85 and 4.2 THz, or about 8.5 percent. Such lasers could be used to detect explosives, which have spectroscopic “fingerprints” in the terahertz range, according to Qin.


On the opposite end of the laser size spectrum, Textron Defense Systems (U.S.A.) is building a 100-kW laser as part of the Pentagon’s Joint High Power Solid State Laser Program. Invited speaker Alex Mandl traced the history of Textron’s efforts from its initial “membership in the kilowatt club” (1.2 kW achieved in February 2004) to its laser’s performance of more than 100 kW in final government tests (exactly how much more, he couldn’t divulge).


Textron calls its technology ThinZag because the beam path inside the laser zigzags through a comparatively thin slab of ceramic (not crystalline) Nd:YAG material. The final laser configuration consists of six ThinZag 15-kW-class lasers in series (yes, 15 × 6 = 90, but again, there may have been other technological tweaks to get it over the 100-kW mark).


Social Media and Postdeadline Papers


I would like to tip my hat to the four CLEO/QELS bloggers – Jim van Howe, Ksenia Dolgaleva, Xiaoyu Miao and David Nugent – who have been contributing to the conference’s social media hub. If you haven’t done so already, please check out their coverage of CLEO/QELS.


Van Howe, a professor at Augustana College in Rock Island, Ill. (U.S.A.), blogged about a couple of postdeadline papers I missed because the room was full and the entryway was clogged. (The paper numbers, though, were QPDA5 and QPDA6.) Since those papers seemed to generate a lot of buzz, I’ll summarize them here.

The group that presented QPDA5, from Yale University (U.S.A.), said that an arbitrary body can be made perfectly absorbing at discrete frequencies, thanks to the interaction of optical absorption and wave interference. “It is thus the time-reversed process of lasing at threshold,” A. Douglas Stone and colleagues wrote.


In QPDA6, Evgenii Narimanov of Purdue University and two colleagues from Norfolk State University (all U.S.A.) found a new approach to the “blacker than black” phenomenon of radiation absorption: something called hyperbolic metamaterials. Hyperbolic dispersion means that a metamaterial has negative electric permittivity in the direction perpendicular to its surface and positive electric permittivity parallel to its surface. The researchers tested their ideas by building an experimental array of silver nanowires.


In the postdeadline session where I did find a space to put myself, Aleksandr Biberman of Columbia University (U.S.A.) described his group’s demonstration of a 40-Gbps electro-optic switch for photonic networks-on-chip (paper CPDA11). Such CMOS-compatible switches will be needed as more photonic networks are built inside the computer as well as between computers. Biberman worked with researchers from both Columbia and Cornell University (U.S.A.).

2010-05 May, CLEO/QELS, Lasers , , , , , , , , , ,