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White-Light Whispering-Gallery-Mode Optical Resonators

Overlapping resonator modes are exploited to obtain wide, high-Q spectra. NASA’s Jet Propulsion Laboratory, Pasadena, California Whispering-gallery-mode (WGM) optical resonators can be designed to exhibit continuous spectra over wide wavelength bands (in effect, white-light spectra), with ultrahigh values of the resonance quality factor (Q) that are nearly independent of frequency. White-light WGM resonators have potential as superior alternatives to (1) larger, conventional optical resonators in ring-down spectroscopy, and (2) optical-resonator/electro-optical modulator structures used in coupling of microwave and optical signals in atomic clocks. In these and other potential applications, the use of white-light WGM resonators makes it possible to relax the requirement of high-frequency stability of lasers, thereby enabling the use of cheaper lasers.

Posted in: Tech Briefs, ptb catchall, Photonics, Briefs

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Middleware Bridges the Optical/Mechanical Design Gap

Mechanical CAD (computer-aided design) programs have become very sophisticated during the past few years. Unfortunately, there is still a portion of the engineering spectrum that cannot be handled well in a traditional CAD program: optical modeling. If you are creating a complicated optical system (think of a camera zoom lens), then it is best to perform almost all of the design in a specialized optical design software program and then transfer the optical design to a CAD program for the later stages of the design process where items like housings, threads, cams, and motors are designed and integrated into the model.

Posted in: Features, ptb catchall, Photonics, Articles

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Photonics Tech Briefs Presents 2005 Products of the Year

Photonics Tech Briefs (PTB) recently presented the 2005 Readers’ Choice Products of the Year at a special awards dinner held at The Water Club in New York City. The top three products chosen by the readers of PTB were honored at the event.

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Tunable, Highly Stable Lasers for Coherent Lidar

Designs have been refined to satisfy competing requirements for stability and tenability. Marshall Space Flight Center, Alabama Practical space-based coherent laser radar systems envisioned for global winds measurement must be very efficient and must contend with unique problems associated with the large platform velocities that the instruments experience in orbit. To compensate for these large platform-induced Doppler shifts in space-based applications, agile-frequency offset-locking of two single-frequency Doppler reference lasers was thoroughly investigated. Such techniques involve actively locking a frequency-agile master oscillator (MO) source to a comparatively static local oscillator (LO) laser, and effectively producing an offset between MO (the lidar slave oscillator seed source, typically) and heterodyne signal receiver LO that lowers the bandwidth of the receiver data-collection system and permits use of very high-quantum-efficiency, reasonably-low-bandwidth heterodyne photoreceiver detectors and circuits. Similar techniques are being applied in atmospheric CO2 differential-absorption lidar work, where MO sources need to be actively offset-locked to CO2 reference cells for continuous absolute-calibration purposes. Active MO/LO offset-locking is also highly applicable to lidar problems involving very high target velocities with respect to a static or moving lidar platform.

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Optical Systems Improve Nerve Stimulation

An infrared laser-based nerve stimulation system eliminates electrical stimulation artifacts, and improves nerve target specificity. Aculight Corporation, Bothell, Washington The stimulation of nerve tissue is a technique that is used in both research and clinical applications. Neuroscientists use nerve stimulation to study the fundamental principles of the nervous system and to research Parkinson’s disease, Alzheimer’s disease, and nerve regeneration, among others. Medical professionals use nerve stimulation for everything from pain and depression management to brain mapping. Today’s stimulators use electrical current to stimulate nerves, resulting in significant limitations. Thanks to a novel optical stimulation technique pioneered by Vanderbilt University, Aculight has developed a compact, laser-based neural stimulator that overcomes these obstacles.

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DPSS UV Source Targets Gas Lasers and Life Sciences

System is designed for applications that relied on pulsed nitrogen gas lasers. Spectra-Physics Corp., Tucson, Arizona Nitrogen lasers have been used for more than 15 years in life science and forensic applications and will continue to play a role in many scientific and industrial applications. But researchers, OEMs, and system integrators working on innovative, cutting-edge applications need higher-performance lasers. The Explorer, a diode-pumped solid-state OEM laser system with flexible power and control electronics, is a low-power, actively Q-switched, ultraviolet (UV) laser system that operates at 349 nm for bioinstrumentation applications that in the past have relied on pulsed nitrogen gas lasers.

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Optical Profilometers Using Adaptive Signal Processing

Sizes would be reduced, leading to development of hand-held profilometers. John F. Kennedy Space Center, Florida A method of adaptive signal processing has been proposed as the basis of a new generation of interferometric optical profilometers for measuring surfaces. Many current optical surface-measuring profilometers utilize white-light-interferometry and, because of optical and mechanical components essential to their operation, are comparable in size to desktop computers. In contrast, the proposed profilometers would be portable, hand-held units. Sizes could be thus reduced because the adaptive-signal-processing method would make it possible to substitute lower-power coherent light sources (e.g., laser diodes) for white light sources and would eliminate the need for most of the optical components of current white-light profilometers. Furthermore, whereas the height scanning ranges of current surface-measuring profilometers are of the order of millimeters, the adaptive-signal-processing method would make it possible to attain scanning ranges of the order of decimeters in the proposed profilometers.

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