Laser Study Shines at Show

Detecting dangerous chemicals with lasers, exploring the brain's circuitry with light, and photoluminescence with nanoneedles will be among the latest breakthroughs in electro-optics, lasers and the application of light waves presented 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.

CLEO, one of the largest exhibitions in the photonics industry, is geared toward laser topics and the electro-optics community and held in conjunction with QELS and the Conference on Photonic Applications, Systems and Technologies (PhAST). The technical presentations attract many to the event, and this year nearly 6000 researchers from around the world will participate.

Scientists presenting CLEO/QELS plenary talks can expect to attract large crowds, as will a symposium in honor of first operable laser inventor and two-time Nobel Prize nominee Theodore Maiman (See also: Maiman Tribute Set at CLEO).

The work of Federico Capasso and his colleagues at Harvard University will be presented in their new paper, "Continuously Tunable Compact Single-Mode Quantum Cascade Laser Source for Chemical Sensing." They are developing a new type of infrared spectrometer that could be just as powerful as today's bulky spectrometry instruments for chemical detection, yet fit inside a shoe box. Instead of using thermal sources for the infrared rays, Capasso's team powered their instrument with 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, and the scientists demonstrated that this small device could identify common chemicals as well as the conventional tabletop instrument. 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 and provide 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.

Three researchers from Brown University will present their work into detecting the brain's intricate microcircuitry using light in their presentation, "Detection of Neural Cell Activity Using Plasmonic Gold Nanoparticles."

Traditionally brain exploration is done by lining up electrodes within or near single neurons to probe their electrical activity, an invasive and often noisy (because of the brain's background electrical activity) method. A number of alternative approaches use optical probes that can detect neuronal activity with light but often require labeling neural cells with electrically-sensitive dyes that may be toxic to neurons. Researchers Jiayi Zhang, Tolga Atay and Arto Nurmikko have created a new type of dye-free optical probe that can directly sense naturally occurring neural activity.

They imbedded gold nanoparticles into tissue culture and showed 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.

In their presentation, "Bright Photoluminescence from GaAs and InGaAs Nanoneedles Grown on Si Substrates," scientists from the University of California, Berkeley, will discuss how they have grown gallium-arsenide (GaAs) structures into the shape of narrow needles which, when optically pumped, emit light with high brightness. The needles (about 3 to 4 µm long, tapering at an angle of 6° to 9° down to tips approximately 2 to 5 nm across) 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 said 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.

Other technical CLEO/QELS topics include: secure communications via space, pushing the optical limits of a microscope, the creation of an optical nuclear magnetic resonance detector, and an update on the status of the National Ignition Facility, the world's largest laser system.

In his CLEO/QELS plenary session Monday, May 5, 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," 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 for Atomic and Molecular Physics (AMOLF), Netherlands, will present "Plasmonics: Optics at the Nanoscale" 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.

Recent developments in quantum optics will be presented by Ian Walmsley, the Hooke Professor of Experimental Physics and head of the sub-department of Atomic and Laser Physics at the University of Oxford, during his plenary talk, "Meet the Fock States: The Photon Revisited," Wednesday, May 7. 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.

CLEO/QELS 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).

For more information, visit: www.cleoconference.org