NOTEWORTHY MEETING PAPERS
At CLEO/QELS, researchers from around the world gather to present many of the latest breakthroughs on the science and engineering of photons and light waves.
Technical highlights during the conference include:
TERAHERTZ BIOCHIP DETECTS ILLICIT DRUGS QUICKLY AND EASILY
A Taiwan research collaboration led by Chi-Kuang Sun (National Taiwan University) has built a tiny biochip that can instantly identify illicit drugs such as cocaine and amphetamines in their natural powdered form.
In the new approach, researchers simply deposit powder in its natural form into a small, rectangular glass-and-plastic biochip containing some electronic components. The deposited powder settles into channels just 20 microns deep, the thickness of just a few red blood cells. Inside the biochip, a small transmitter beams electromagnetic radiation in the terahertz (THz) range (in between the microwave and infrared), to which biomolecules are very sensitive. By recording how much radiation the powder absorbs over a range of THz frequencies, the researchers obtain distinctive chemical fingerprints of the biomolecules that make up the powder.
Using this method, the researchers were able to distinguish powders of cocaine (which absorbs a maximum of radiation at 0.8 THz) and amphetamine (1.03 THz) from powders of potato starch, flour, and lactose, the latter of which absorbs a maximum of radiation at 0.53 THz. Only 2-5 seconds were required to finish each scan. In addition, the drug's distinctive THz signatures makes them possible to detect even if they were mixed in with an additional ingredient such as flour.
Present forensics techniques such as gas chromatography, in addition to being potentially bulky, all require tampering with the sample, by vaporizing it, for example, or attaching a fluorescent molecule to it. This can add time, expense, and complication to the process of identifying a drug. The new terahertz technique could solve these problems and be a more efficient alternative.
Demonstrating improved sensitivity in recent experiments, the biochip could also identify specific molecules dissolved in water (which tends to absorb terahertz radiation strongly and obscure the signals from other molecules) for potential applications such as DNA identification in saliva. For such applications, the portability and potentially low cost of this biochip make it superior to conventional techniques.
Forensics is not the only application for the terahertz biochip: researchers also believe it may be very useful for molecular biology applications, such as studying the folding patterns of proteins, which would be helpful for designing new drugs. (Paper CMLL7, "Terahertz Biochip for Illicit Drug Detection")
HIGH-SPEED TERAHERTZ IMAGER FOR REAL-WORLD APPLICATIONS
In an approach that has already improved nondestructive evaluation of the space shuttle and can potentially bring about better detection of weapons and explosives for homeland security, David Zimdars of Michigan-based Picometrix will present a fast and practical real-world system for terahertz (THz) imaging. THz imaging employs a band of electromagnetic radiation between the microwave and infrared spectrum to penetrate objects and look inside them. This form of imaging has a number of advantages over other methods currently in practice, including safety (no ionizing radiation, unlike x-ray systems), resolution of details (about a millimeter in size), and a better ability to discriminate between similar materials (such as plastic explosives and fertilizer).
Previous THz systems were confined to the laboratory, and took dozens of minutes or hours to image small samples (less than 10 square centimeters in size). In contrast, the new system can inspect a 1-square-meter area with 1.5-mm resolution in less than an hour, while smaller areas take just a few minutes. NASA engineers have already used the Picometrix design to peer through the layer of spray-on foam insulation on the external fuel tanks of the space shuttle Discovery and inspect it for defects. The terahertz imager is also fast enough for monitoring certain high-speed industrial processes. For example, the system can now be used to inspect paper products moving on an assembly line at 4 m/s with 1 mm spacing. The new system works in the "time domain"; it obtains information at different points in time to build up an image. In the Picometrix system, laser pulses lasting just femtoseconds travel through an optical fiber to deposit energy onto a semiconductor material which then generates THz radiation. The semiconductor material then aims THz rays at different areas of the object (which can remain stationary, unlike in previous methods where the object had to move during a scan).
The system has two modes. The "transmission" mode can inspect items to depths of up to 30 cm when they do not contain significant amounts of water or metal. In that mode, the detector obtains images by recording how much of the terahertz rays get absorbed by an object. Reflection mode is useful when it is only possible to inspect one side of an object (such as clothing on a person). In that mode, the detector records THz rays reflected from the object of interest. The researchers expect it to be possible to develop much faster versions of this system for homeland security applications, such as airline screening of passengers and luggage. (CMLL1, "Security and Non Destructive Evaluation Application of High Speed Time Domain Terahertz Imaging")
PROBING THE ORIGIN OF EARTH'S CIRRUS CLOUDS AND LIFE ON MARS
In an advance that enables heightened monitoring of planetary atmospheres, for the first time researchers have designed new lightweight laser instruments that make it practical to routinely measure concentrations of atmospheric gases in situ, or in their natural environments. Measuring these gases more widely and frequently will give atmospheric researchers much richer information for studying weather, climate change, and other phenomena on Earth and other planets and moons. The instruments, known as tunable mid-IR laser spectrometers, produce light in the mid-infrared region, a part of the spectrum to which all atmospheric gases respond in a distinctive fashion. Tuning the lasers to produce light in a particular window of the mid-IR spectrum and recording the colors (wavelengths) that the atmosphere absorbs makes it very easy to obtain direct information on the concentration of different gases that are present, a boon to climate researchers who are accustomed to making limited or painstaking measurements of the upper atmosphere's crucial chemistry.
Using a laser spectrometer on NASA's high altitude WB-57 spacecraft, Christopher Webster of the Jet Propulsion Laboratory and his colleagues have made the first-ever in situ measurements of different water isotopes in and out of the clouds from the troposphere to stratosphere. This information is providing a wealth of data on the still incompletely understood origin of cirrus clouds, the wispy masses that play a major role in warming the Earth. The laser instruments can capture signatures of the clouds' "birth," thereby enabling the researchers to determine whether the clouds formed from ice lofted up from below, or if they built up at their present location under the right conditions of temperature and moisture. Identifying cirrus cloud locations--and the details of how any given cloud formed, something that was difficult to do before--is very important to understanding their contribution to global temperatures.
Webster has also designed a tunable laser spectrometer for the upcoming Mars Science Laboratory mission set for launch in 2009. Among other things, the instrument will probe the recently discovered methane gas in the Martian atmosphere. By measuring the ratio of carbon-13 to carbon-12 in the methane gas, researchers will be able to distinguish whether it came from Martian rocks or from methane-producing microorganisms that may have existed on the planet.
Much of the breakthrough with these new instruments arises from the fact that one can now fit several of these tunable mid-IR lasers in a 5-lb, room-temperature package, as opposed to the technology of the 1980s, which required a 3000-lb., liquid-helium-cooled environment for a single laser, or even that of the 1990s, in which the laser setups were still hundreds of pounds in weight. In contrast, the small, lightweight, and room-temperature nature of the new instruments opens the possibility of deploying many of them at the same time to get abundant climate data simultaneously at multiple locations.
(Paper CFL1, "Advanced Mid-IR Laser Spectrometers for Identifying the Origin of Earth's Cirrus Clouds and Life on Mars")
RECORD-BREAKING TABLETOP MICROSCOPE PROMISES TO BRING IMPORTANT NANODEVICES, COMPUTER CHIPS INTO SHARPER VIEW
Using state-of-the-art extreme ultraviolet laser technology, Courtney Brewer of Colorado State University and her colleagues have built a tabletop optical imaging system that can reveal details smaller than 38 nanometers (billionths of a meter) in size, a world record for a compact light-based optical microscope. The microscope can keenly inspect nanometer-scale devices designed for electronics and other applications. It will also be capable of catching subtle manufacturing defects in today's ultra-miniaturized computer circuits, where defects just 50 nm in size that were once too small to cause trouble could wreak havoc in the nanometer scales of today's computer chips.
Except for some high-tech details, the microscope works very similarly to a conventional optical microscope. Light shines through the sample of interest. The transmitted light gets collected by an "objective zone plate," which forms an image on a CCD detector, the same kind of device that records images in a digital camera.
However, in the case of the sub-38-nm microscope, there are some advanced technological twists. The microscope uses a laser that produces light in the extreme-ultraviolet (EUV) spectrum, whose very small wavelength makes it possible to see a sample's tiny details. The EUV light is created by ablating (boiling away) the surface of a silver or cadmium target material so that the vaporized material forms a plasma (collection of charged particles) that radiates laser light. To focus this light, the researchers avoid standard lenses, because they strongly absorb EUV radiation. Instead, the microscope uses "diffractive zone plates," structures containing nanometer-spaced concentric rings that focus the light in the desired fashion.
Other state-of-the-art optical microscopes have achieved resolutions as low as 15 nm, but they required the use of large particle accelerators called synchrotrons. This more compact and less expensive system has the potential to become more widely available to researchers and industry. In addition, since the extreme ultraviolet laser produces light pulses with very short duration (4 picoseconds, or trillionths of a second), the researchers believe it may be possible to create picosecond-scale snapshots of important processes in other applications. The work was done at Colorado State University in collaboration with the University of California Berkeley as part of the NSF ERC for Extreme Ultraviolet Science and Technology. (Paper CME4, "Sub-38 nm resolution microscopy with a tabletop 13 nm wavelength laser")
ORBITAL TOMOGRAPHY: FAST LASERS SET SIGHTS ON ELECTRON CLOUDS
Electrons orbiting an atomic nucleus are often depicted concretely but incorrectly as little planets circling a miniature sun in crisp trajectories. Actually, quantum mechanics provides a more accurate (but still metaphorical) picture: the electrons can't be depicted directly. Rather, only the probability of their being at certain places near the nucleus (the core of the atom) can be rendered and even then only as cloudlike blobs. Researchers never had access to actual images of electron clouds--they only calculated them in theory. Thanks to breakthroughs with ultrashort laser pulses, these clouds, called orbitals, can now be imaged directly.
David Villeneuve of the National Research Council of Canada and his colleagues have helped pioneer a method in which a femtosecond laser pulse rips electrons from the periphery of molecules. These electrons, feeling the electric field of the pulsed light, are first repelled but then very quickly recalled to their home molecule by the strong fields of the same pulse which, in its quick cycling, reverses direction. The electrons can then recombine into the parent molecule, and in the process emit extreme ultraviolet light of their own, light which can be used to perform a type of "tomographic" imaging of the molecule, or more particularly its orbitals. Thus the electron is used to image its own domain. Villeneuve will report on his latest efforts to map orbitals and progress towards making movies of molecular dynamics. (Paper JFB1, "Imaging of Molecular Orbitals and Attosecond Pulses.")
ADDITIONAL NOTEWORTHY TOPICS
Additional noteworthy meeting topics include biologically inspired optical polymers (CThI2), construction of the highest-powered laser in the world (JTuG1), a 3D-2D-3D photonic crystal (CTuAA1), using optics to improve accuracy in determining blood flow rate (CTuW2), innovations in solid-state lighting (CTuDD2), airborne lidar and satellite comparison of atmospheric aerosols (CThT4), the light-emitting field-effect transistor (CTuDD1), optical magnetic mirror (QWE2), nanowell structures for sensing tiny particles (CWL1), an optical lattice clock (QThC4), entangled photons on demand from a single quantum dot (JTuC2), matter wave optics on an atom chip (QThC2), solid-state single photon detectors (JTuF), and nanoplasmonics (session QMC).
PLENARY SESSION HIGHLIGHTS
Taking place throughout the meeting, three plenary talks will feature a mixture of speakers and topics. In "The Mars Laser Communications Demonstration Project" (Wednesday, May 24), Don Boroson of MIT Lincoln Lab will explain technology that could allow spacecraft to transmit high rates of data via light waves, rather than with conventional radio waves, and discuss how this space technology will influence future laser communications systems. In "Fiber Lasers: The Next Generation" (Monday, May 22), David Payne of the University of Southampton will describe how lasers which use fiber optics to generate beams will have substantial impacts beyond applications which they have already affected, such as laser cutting and welding, and may move into many niches that traditional laser designs currently occupy. In "Quantum Phenomena in Optical Communications Systems: Is the Quantum Internet Next?" (Wednesday, May 24), Richart E. Slusher, Lucent Technologies Inc., will discuss how light's quantum properties are being exploited for use in powerful new encryption, computing, and communications technologies.
ONSITE PRESS INFORMATION
A Press Room will be located in the Long Beach Convention Center in VIP A. The Press Room will be open Sunday, May 21 from 12 p.m. - 4 p.m. and Monday, May 22 through Thursday, May 25 from 7:30 a.m. - 6 p.m. Those interested in obtaining a meeting badge for the Press Room should register online at http://www.cleoconference.org/media_center/MediaRegistrationForm.aspx or contact OSA's Colleen Morrison at 202.416.1437, email@example.com.
A press luncheon panel will take place on Tuesday, May 23 at noon. The press luncheon will offer an overarching perspective on significant new developments to be unveiled during CLEO/QELS. The panel will also introduce some of the most promising applications for optical technology. To register for the press luncheon contact OSA's Colleen Morrison at firstname.lastname@example.org, 202.416.1437.
Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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