Photonics/Optics

Using Whispering-Gallery-Mode Resonators for Refractometry

Refractive and absorptive properties are inferred by correlating predictions with measurements. NASA’s Jet Propulsion Laboratory, Pasadena, California A method of determining the refractive and absorptive properties of optically transparent materials involves a combination of theoretical and experimental analysis of electromagnetic responses of whispering-gallery-mode (WGM) resonator disks made of those materials. The method was conceived especially for use in studying transparent photorefractive materials, for which purpose this method affords unprecedented levels of sensitivity and accuracy. The method is expected to be particularly useful for measuring temporally varying refractive and absorptive properties of photorefractive materials at infrared wavelengths. Still more particularly, the method is expected to be useful for measuring drifts in these properties that are so slow that, heretofore, the properties were assumed to be constant.

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Focusing Light Beams To Improve Atomic-Vapor Optical Buffers

Atomic-vapor optical buffers could be made to perform more nearly optimally. NASA’s Jet Propulsion Laboratory, Pasadena, California Specially designed focusing of light beams has been proposed as a means of improving the performances of optical buffers based on cells containing hot atomic vapors (e.g., rubidium vapor). There is also a companion proposal to improve performance by use of incoherent optical pumping under suitable conditions.

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Digitally Enhanced Heterodyne Interferometry

This design mitigates cyclic error and improves measurement sensitivity. NASA’s Jet Propulsion Laboratory, Pasadena, California Spurious interference limits the performance of many interferometric measurements. Digitally enhanced interferometry (DEI) improves measurement sensitivity by augmenting conventional heterodyne interferometry with pseudo-random noise (PRN) code phase modulation. DEI effectively changes the measurement problem from one of hardware (optics, electronics), which may deteriorate over time, to one of software (modulation, digital signal processing), which does not. DEI isolates interferometric signals based on their delay. Interferometric signals are effectively time-tagged by phase-modulating the laser source with a PRN code. DEI improves measurement sensitivity by exploiting the autocorrelation properties of the PRN to isolate only the signal of interest and reject spurious interference. The properties of the PRN code determine the degree of isolation.

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Photochemical Tissue Bonding for Military Medical Applications

A two-wavelength laser and albumen stent easily repair separated vessels.Joining severed vessels is a recurring problem in trauma and surgery. The basic technology of joining vessels using sutures has been available for centuries, but remains a slow and tedious process. A complete system for micro-anastomosis of vessels was developed that involves a laser in a clinically useful form factor, and a novel albumen stent to support the vessel during the surgery.

Posted in: Bio-Medical, Briefs, TSP, Briefs, TSP, Photonics

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Multiparallel Three-Dimensional Optical Microscopy

Lyndon B. Johnson Space Center, Houston, Texas Multiparallel three-dimensional optical microscopy is a method of forming an approximate three-dimensional image of a microscope sample as a collection of images from different depths through the sample. The imaging apparatus includes a single microscope plus an assembly of beam splitters and mirrors that divide the output of the microscope into multiple channels. An imaging array of photodetectors in each channel is located at a different distance along the optical path from the microscope, corresponding to a focal plane at a different depth within the sample. The optical path leading to each photodetector array also includes lenses to compensate for the variation of magnification with distance so that the images ultimately formed on all the photodetector arrays are of the same magnification.

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Sub-Aperture Interferometers

Multiple target sub-beams are derived from the same measurement beam. NASA’s Jet Propulsion Laboratory, Pasadena, California Sub-aperture interferometers — also called wavefront-split interferometers — have been developed for simultaneously measuring displacements of multiple targets. The terms “sub-aperture” and “wavefront-split” signify that the original measurement light beam in an interferometer is split into multiple sub-beams derived from non-overlapping portions of the original measurement- beam aperture. Each measurement sub-beam is aimed at a retroreflector mounted on one of the targets. The splitting of the measurement beam is accomplished by use of truncated mirrors and masks, as shown in the example below.

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Vacuum-Compatible Wideband White Light and Laser Combiner Source System

NASA’s Jet Propulsion Laboratory, Pasadena, California For the Space Interferometry Mission (SIM) Spectrum Calibration Development Unit (SCDU) testbed, wideband white light is used to simulate starlight. The white light source mount requires extremely stable pointing accuracy (hts were coupled to a photonic crystal fiber (PCF).

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