April 24, 2008, San Jose, CA--Nearly 6,000 researchers from around the world will present the latest breakthroughs in electro-optics, lasers, and the application of light waves at the 2008 Conference on Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference (CLEO/QELS) May 4-9 at the San Jose McEnery Convention Center in San Jose, Calif.
CLEO is the preeminent event for those in the lasers and electro-optics community. It will be held in conjunction with QELS and the Conference on Photonic Applications, Systems and Technologies (PhAST). The meeting is co-sponsored by the Optical Society (OSA), the American Physical Society Division of Laser Science (APS-DLS), and the IEEE Lasers & Electro-Optics Society (IEEE/LEOS).
Some of the many technical highlights at the meeting include shining light on the brain's activity, tiny laser arrays for sensitive chemical detection, secure communications via space, photoluminescence in nano-needles, and the world's largest laser facility (National Ignition Facility).
Additional research news summaries can be found online at the CLEO media center.
SHINING LIGHT ON THE BRAIN'S ACTIVITY
The microscopic structure of the human brain is almost incomprehensibly complicated, composed of trillions of interconnections between tens of billions of neurons. Understanding this circuitry, the aim of modern neuroscience, is a laudable goal for fundamental as well as neurological health care reasons.
Exploring the brain's microcircuitry has traditionally been done by lining up tiny electrodes to single neurons to probe their electrical activity. Though well established, this method is invasive and often noisy because of background electrical activity in the brain. A number of alternative approaches use optical probes that can detect neuronal activity with light, but these methods often require labeling neural cells with electrically-sensitive dyes that may be toxic to neurons.
Now Jiayi Zhang, Tolga Atay, and Arto Nurmikko at Brown University (Providence, RI) have created a new type of dye-free optical probe that can directly sense naturally occurring neural activity. They have embedded gold nanoparticles into tissue culture and shown that they can measure the electrical activity of live neurons. The technique takes advantage of a phenomenon known as surface plasmon polariton resonance, a sharp spectroscopic resonance at visible/near-infrared wavelengths. Basically, the gold nanoparticles are used to optically sense the local electric fields produced when nearby neurons fire. The neuronal activity modulates the electron density at the surface of the nanoparticle, which causes an observable spectral shift that the researchers can monitor. (Talk CWM3, "Detection of Neural Cell Activity Using Plasmonic Gold Nanoparticles.")
TINY LASER ARRAYS FOR SENSITIVE CHEMICAL DETECTION
Early miners used to carry canaries into coal mines because the birds were sensitive to certain gasses. Modern chemical analysis does the same thing, though much more powerfully. For instance, infrared spectroscopy can detect even trace amounts of a wide range of chemicals, including toxic components of hazardous waste or chemical weapons, because many chemicals absorb light in the mid-infrared band.
Now Federico Capasso and his colleagues at Harvard University are developing a new type of infrared spectrometer that could be just as powerful as these bulky instruments yet fit inside a shoe box. Instead of using thermal sources for infrared rays, a team lead by Capasso, his student Benjamin G. Lee, and his postdoctoral fellow Mikhail A. Belkin, has built one of these instruments, which is powered by a tiny array of infrared quantum cascade lasers on a chip smaller than a dime. The chip holds an array of 32 lasers, each emitting a distinct wavelength and together covering a broad spectral range in the infrared region. The researchers' new paper demonstrates that their device could identify common chemicals as well as a conventional tabletop instrument, which has a much larger footprint. It is the first time that a laser of this type, capable of such performance, has been reported.
The advantage of using a laser source is that lasers are much brighter than thermal sources thus providing a higher signal-to-noise ratio. The lasers can also be fine-tuned to provide wavelengths on demand to scan accurately for chemicals of interest--akin to having thousands of canaries, each capable of detecting a range of chemicals. (Talk CMH1, "Continuously Tunable Compact Single-Mode Quantum Cascade Laser Source for Chemical Sensing.")
SECURE COMMUNICATIONS VIA SPACE
The exchange of information between distant sources is the basis of all communications, but quantum mechanics may open up this distant exchange as never before. Quantum key distribution, for instance, would allow for absolutely secure encryption of information exchange by encoding information keys on single photons. These photons are so sensitive that there is physically no way to undetectably tamper with them as they travel from sender to receiver. Teleportation of quantized states is another possible application. This would allow future quantum computers to be interconnected using the properties of individualized photons or other quanta.
To achieve this type of technology, an exchange of single quanta between a sender and a remote receiver must occur. Already, some companies have explored ways of achieving quantum key distribution over fiber optics, but it has never been done using satellites. Paolo Villoresi and his colleagues at the University of Padova in Italy, in collaboration with the group of Anton Zeilinger in Austria, have taken the first step to establishing quantum communications in space by exchanging single photons from an orbiting satellite to Earth. They demonstrated how the Matera Laser Ranging Observatory in Matera, Italy, used for satellite laser ranging with ultimate precision, can be adapted as a quantum communication receiver to detect single quanta emitted by an orbiting source--in this case a Japanese low-Earth-orbiting satellite. They also identified the exact techniques needed to detect the very weak quantum signal to be exploited in a dedicated satellite. (Talk QWB3, "Experimental Study of a Quantum Channel from a LEO Satellite to the Earth.")
PHOTOLUMINESCENCE IN NANO-NEEDLES
Silicon is the workhorse among semiconductors in electronics. But in opto-electronics, where light signals are processed along with electronic signals, a semiconductor that is capable of emitting light is needed, which silicon can't do very well. Here gallium-arsenide (GaAs) is the workhorse, especially in the creation of light-emitting diodes (LED) and LED lasers.
Scientists at the University of California, Berkeley have now grown GaAs structures into the shape of narrow needles which, when optically pumped, emit light with high brightness. The needles are approximately 3 to 4 microns long and taper at an angle of 6 to 9 degrees down to tips approximately 2 to 5 nm across. These needles are not yet lasers; creating them will be the next step. This represents the first time a lab has been able to fashion GaAs into a defect-free crystal structure (technical name: wurtzite) exactly like this on a silicon substrate and without the use of catalysts.
Lead researcher Michael Moewe says that, in addition to optoelectronic devices, he expects the needles to be valuable in such applications as atomic force microscopy (AFM), where the sharp tips can be grown in arrays without further etching or processing steps. Some believe that AFM arrays, besides speeding up the recording of nearly atomic-resolution images of surfaces (allowing one to create atomic movies), might be used to create a new form of data storage by influencing the atoms in the sample. The needles also may be used in producing tip-enhanced Raman spectroscopy. Raman spectroscopy is a process in which the energy levels of molecules are determined by shining light at a known frequency into the sample and then observing the frequency of the outgoing light. Delivering light from a sharp tip allows a much more targeted examination of the sample, possibly even permitting the spectroscopic study of single molecules. (Talk CTuCC1, "Bright Photoluminescence from GaAs and InGaAs Nanoneedles Grown on Si Substrates.")
NATIONAL IGNITION FACILITY—THE WORLD'S LARGEST LASER SYSTEM
The National Ignition Facility at Lawrence Livermore National Laboratory (LLNL), a project more than a decade in the making, is scheduled for completion in March 2009. When it goes online, 192 laser beams will generate millions of joules of infrared light, which will in turn be converted to ultraviolet light just prior to reaching the focus of these lasers. Electro-optical devices will time, shape, and direct this light. In a facility the size of three football fields, the light will go through a tiny hole into a target made of gold and uranium. This target has the shape of a soda can, but is less than one inch in height. There the light will paint the inside walls of this chamber, heating the metal walls and causing them to emit X-rays that will fill the can, bombard a small plastic capsule in the can's center, implode the capsule, and trigger the fusion of tritium and deuterium inside.
Lead researcher Christopher A. Haynam with LLNL will focus on the status of the light that will drive this operation--by far the largest laser system in the world. So far, about three quarters of the lasers have been installed. These lasers have been operated to more than 3.1 million joules total energy in the infrared. A few beams have been pointed to a target, and a number of low-energy shots taken and converted to the ultraviolet to check their alignment. If it works as it is supposed to, the National Ignition Facility will be able to achieve temperatures and pressures that emulate conditions in the interior of planets or stars. (Talk CFQ1, "The National Ignition Facility: Status and Performance of the World's Largest Laser System for the High Energy Density and Inertial Confinement Fusion.")
CLEO/QELS/PHAST PLENARY SPEAKERS
David Reitze, professor of physics at the University of Florida, will present "The Laser Interferometer Gravitational-Wave Observatory: Probing the Dynamics of Space-Time with Attometer Precision" on Monday, May 5, about the detection of gravitational waves, which promises to open up a new astrophysical window to the universe. He will discuss gravitational waves, what makes them so interesting and challenging to detect and how researchers will detect them using "really big interferometers."
Albert Polman, director of the Center for Nanophotonics, FOM-Institute AMOLF, Netherlands, will present "Plasmonics: Optics at the Nanoscale" on Wednesday, May 7, about the generation, concentration, and dispersion of surface plasmons in thin metal films, nanoresonators, and metal particle arrays. The unique dispersion and mode confinement characteristics of these structures enable control of light at the true nanoscale.
Ian Walmsley, the Hooke Professor of Experimental Physics and head of the Sub-Department of Atomic and Laser Physics at the University of Oxford, will present "Meet the Fock States: The Photon Revisited" on Wednesday, May 7, about recent developments in quantum optics. These developments have enabled the generation of exotic non-classical states of light that can provide a new perspective on the character of the photon.
For more information, visit the Conference's Web site.