Photonics/Optics

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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Generalized-Time-Line Program for Planning and Scheduling

Generalized Timelines API is a computer program that provides (1) a means of representing arbitrary realworld state and resource information for use in planning, scheduling, and plan- and schedule-executing software and (2) an application-programming interface (API) that accelerates the development and validation of the software. In prior time-line programs, constraints had not been regarded as parts of time lines, and it was difficult to represent constraints. For the present program, a time line is defined as a representation of the actual and/or predicted value(s) of a variable and a set of constraints on the variable, both at successive intervals of time. The program (1) enables assignment of values to variables and modeling of the constraints on the variables, all as functions of time; (2) makes it possible to determine whether the values are consistent with the constraints; and (3) provides “hooks” to the search space represented by the variables for the purpose of optimizing plans. This program enables computer-programming specialists to engage in research on, and development of, scheduling application programs separately from the efforts of other specialists to implement time lines specific to their domains of expertise. In comparison with prior software of the same type, this program is representationally sufficient for more domains.

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

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Simultaneous Ultra Fast Framing and Streak Imaging

The ability to record simultaneous framing images and streak images has long been a requirement in the research fields of detonation, electrical discharge, biomedical and many other applications. Early systems incorporating both framing and streak cameras used external beam splitting optics with light gathering limitations that required critical alignment of the external splitting optics. Later systems incorporated framing cameras and streak cameras, built into one mainframe, using available beam splitters. This allowed for simultaneous framing and streak, however, this type of beam splitter limited access to streak optics, and primarily limited the performance of the streak camera due to the smaller format streak tubes.

Posted in: Articles, Features, ptb catchall, Photonics

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