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Spectral vs. Coherent Beam Combining: How Do They Compare?

Partial reflectors in interferometers and polarization-sensitive devices (beam splitters used in reverse) such as beam-splitting cubes are common examples of systems that combine two beams (adding beams so that they are co-linear). While these components perform beam combining, they typically are inefficient and/or limited in the number of beams that can be combined. Polarization beam combining, for instance, only works with two beams because the light has only two distinguishable states.

Posted in: Features, ptb catchall, Photonics, Articles

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Optics Program Modified for Multithreaded Parallel Computing

NASA’s Jet Propulsion Laboratory, Pasadena, California A powerful high-performance computer program for simulating and analyzing adaptive and controlled optical systems has been developed by modifying the serial version of the Modeling and Analysis for Controlled Optical Systems (MACOS) program to impart capabilities for multithreaded parallel processing on computing systems ranging from supercomputers down to Symmetric Multiprocessing (SMP) personal computers. The modifications included the incorporation of OpenMP, a portable and widely supported application interface software, that can be used to explicitly add multithreaded parallelism to an application program under a shared-memory programming model. OpenMP was applied to parallelize ray-tracing calculations, one of the major computing components in MACOS. Multithreading is also used in the diffraction propagation of light in MACOS based on p-threads [POSIX Thread, (where “POSIX” signifies a portable operating system for UNIX)]. In tests of the parallelized version of MACOS, the speedup in ray-tracing calculations was found to be linear, or proportional to the number of processors, while the speedup in diffraction calculations ranged from 50 to 60 percent, depending on the type and number of processors. The parallelized version of MACOS is portable, and, to the user, its interface is basically the same as that of the original serial version of MACOS.

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

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Enhanced-Contrast Viewing of White-Hot Objects in Furnaces

Band-pass- and polarization-filtered laser light exceeds polarization-suppressed blackbody light. Marshall Space Flight Center, Alabama An apparatus denoted a laser image contrast enhancement system (LICES) increases the contrast with which one can view a target glowing with blackbody radiation (a white-hot object) against a background of blackbody radiation in a furnace at a temperature as high as ≈1,500 °C. The apparatus utilizes a combination of narrowband illumination, along with band-pass filtering and polarization filtering to pass illumination reflected by the target while suppressing blackbody light from both the object and its background.

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

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Dual-Laser-Pulse Ignition

This scheme provides a more reliable ignition source and more efficient energy delivery than a single-pulse format. Marshall Space Flight Center, Alabama A dual-pulse laser (DPL) technique has been demonstrated for generating laser-induced sparks (LIS) to ignite fuels. The technique was originally intended to be applied to the ignition of rocket propellants, but may also be applicable to ignition in terrestrial settings in which electric igniters may not be suitable. Laser igniters have been sought as alternatives to such conventional devices as electrical spark plugs and torch igniters for the following main reasons:

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

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Few-Mode Whispering-Gallery-Mode Resonators

Simple structures function similarly to single-mode optical fibers. NASA’s Jet Propulsion Laboratory, Pasadena, California Whispering-gallery-mode (WGM) optical resonators of a type now under development are designed to support few well-defined waveguide modes. In the simplest case, a resonator of this type would support one equatorial family of WGMs; in a more complex case, such a resonator would be made to support two, three, or some other specified finite number of modes. Such a resonator can be made of almost any transparent material commonly used in optics. The nature of the supported modes does not depend on which material is used, and the geometrical dispersion of this resonator is much smaller than that of a typical prior WGM resonator. Moreover, in principle, many such resonators could be fabricated as integral parts of a single chip.

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

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Tapered Waveguides Improve Fiber Light Coupling Efficiency

Two-dimensional tapers in silicon waveguides improve coupling efficiency to optical fibers. Molex Inc., Downers Grove, Illinois and KiloLambda Technologies Ltd., Tel Aviv, Israel Silicon waveguides have strong light confinement properties due to a very high index core (silicon, refractive index ~3.5) material surrounded by a much lower index glass (silica, refractive index ~1.5) cladding. Due to this property, silicon waveguides can turn light paths through sharp bends without suffering any appreciable loss. This enables miniaturization of functional optical components and enhances dense integration of devices on waveguide chips.

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

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Electrically Tunable Terahertz Quantum-Cascade Lasers

These devices would supplant gas lasers as far-infrared sources. NASA’s Jet Propulsion Laboratory, Pasadena, California Improved quantum-cascade lasers (QCLs) are being developed as electrically tunable sources of radiation in the far infrared spectral region, especially in the frequency range of 2 to 5 THz. (Heretofore, the wavelengths of QCLs have been adjusted by changing temperatures, but not by changing applied voltages or currents.) In comparison with gas lasers now used as far-infrared sources, these QCLs would have larger wavelength tuning ranges, would be less expensive, and would be an order of magnitude less massive and power-hungry. It is planned to use the improved QCLs initially as the active components of local oscillators in spaceborne heterodyne instruments for studying infrared spectral lines of molecules of scientific interest. On Earth, the QCLs could be used as far-infrared sources for medical glucose-monitoring and heart-monitoring instruments, chemical-analysis and spectral-imaging systems, and imaging instruments that exploit the ability of terahertz radiation to penetrate cloth and walls for detection of contra-band weapons.

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