Photonics/Optics

Micromachining with Lasers

Laser micromachining involves using light to remove material. Lasers can also be used in many other applications such as welding, marking, additive manufacturing and surface alteration, but these fall outside the definition. As a general rule, laser micromachining involves working on substrates that are less than 1 mm in thickness — usually much less — and feature sizes that are also less than 1 mm, with the lower end on the order of a few microns.

Posted in: Articles, Features, ptb catchall, Photonics

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Measuring LED and Solid State Lighting Performance

Light emitting diodes (LEDs) and solid state lighting (SSL) products that incorporate LEDs pose many measurement challenges compared with other lighting elements, such as traditional tungsten and fluorescent. Advanced optical radiation measurement equipment and new techniques are often required to determine basic photo-metric and colorimetric parameters for LEDs and SSL products. Updated measurement instrumentation, calibration and performance characterization methods have allowed for improvement in the repeatability and reproducibility of measurements of average LED intensity, total luminous flux and colorimetric quantities. Lower uncertainty, detector-based standards provide a convenient transfer and monitoring from primary measurement standards.

Posted in: Application Briefs, Applications, ptb catchall, Photonics

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Metrology System for a Large, Somewhat Flexible Telescope

This system would measure focal-plane position errors caused by structural deformations. NASA’s Jet Propulsion Laboratory, Pasadena, California A proposed metrology system would be incorporated into a proposed telescope that would include focusing optics on a rigid bench connected via a deploy- able mast to another rigid bench holding a focal-plane array of photon counting photodetectors. Deformations of the deployable mast would give rise to optical misalignments that would alter the directions (and, hence, locations) of incidence of photons on the focal plane. The metrology system would measure the relative displacement of the focusing-optics bench and the focal-plane array bench. The measurement data would be used in post-processing of the digitized photodetector outputs to compensate for the mast-deformation-induced changes in the locations of incidence of photons on the focal plane, thereby making it possible to determine the original directions of incidence of photons with greater accuracy.

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

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Formation Flying of Components of a Large Space Telescope

NASA’s Jet Propulsion Laboratory, Pasadena, California A conceptual space telescope having an aperture tens of meters wide and a focal length of hundreds of meters would be implemented as a group of six separate optical modules flying in formation: a primary-membrane-mirror module, a relay-mirror module, a focal-plane-assembly module containing a fast steering mirror and secondary and tertiary optics, a primary-mirror-figure-sensing module, a scanning-electron-beam module for controlling the shape of the primary mirror, and a sunshade module. Formation flying would make it unnecessary to maintain the required precise alignments among the modules by means of an impractically massive rigid structure. Instead, a control system operating in conjunction with a metrology system comprising optical and radio sub-systems would control the firing of small thrusters on the separate modules to maintain the formation, thereby acting as a virtual rigid structure. The control system would utilize a combination of centralized- and decentralized-control methods according to a leader-follower approach.

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

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Laser Metrology Heterodyne Phase-Locked Loop

NASA’s Jet Propulsion Laboratory, Pasadena, California A method reduces sensitivity to noise in a signal from a laser heterodyne interferometer. The phase-locked loop (PLL) removes glitches that occur in a zero-crossing detector’s output [that can happen if the signal-to-noise ratio (SNR) of the heterodyne signal is low] by the use of an internal oscillator that produces a square-wave signal at a frequency that is inherently close to the heterodyne frequency.

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

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Precise Stabilization of the Optical Frequency of WGMRs

This technique results in whispering gallery mode resonators with absolute frequency stability. NASA’s Jet Propulsion Laboratory, Pasadena, California Crystalline whispering gallery mode resonators (CWGMRs) made of crystals with axial symmetry have ordinary and extraordinary families of optical modes. These modes have substantially different thermo-refractive constants. This results in a very sharp dependence of differential detuning of optical frequency on effective temperature. This frequency difference compared with clock gives an error signal for precise compensation of the random fluctuations of optical frequency. Certain crystals, like MgF2, have “turnover” points where the thermo-refractive effect is completely nullified.

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

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Spatial Modulation Improves Performance in CTIS

Computed spectra are more accurate when scenes have spatial structure. NASA’s Jet Propulsion Laboratory, Pasadena, California Suitably formulated spatial modulation of a scene imaged by a computed-tomography imaging spectrometer (CTIS) has been found to be useful as a means of improving the imaging performance of the CTIS. As used here, “spatial modulation” signifies the imposition of additional, artificial structure on a scene from within the CTIS optics.

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

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