Physical Sciences

Lightweight, Segmented, Mostly Silicon Telescope Mirror

A document presents the concept of a curved telescope primary reflector structure, made mostly of silicon, that would have an areal mass density = 1 kg/m2 and would be deployed in outer space, where it would be operated at a temperature in the cryogenic range. The concept provides for adjustment of the shape of the mirror to maintain the required precise optical surface figure despite the flexibility inherent in the ultra-lightweight design. The structure would include a thin mirror layer divided into hexagonal segments supported by flexure hinges on a lightweight two-layer backing structure. Each segment would also be supported at three points by sets of piezoelectric linear microactuators that could impose small displacements along the optical axis. The excitations applied to the aforementioned microactuators would be chosen to effect fine adjustments of the axial positions and the orientations of the segments relative to the supporting structure. Other piezoelectriclinear microactuators embedded in the backing structure would enable control of the displacements of the segmentsalong the hexagonal axes; they would also enable control of the curvature ofthe backing structure and, thus, additional control of the curvature of the reflector.

Posted in: Physical Sciences, Briefs

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Kalman Filter for Calibrating a Telescope Focal Plane

Optimal estimates of scientific and engineering calibration parameters are generated simultaneously. The instrument-pointing frame (IPF) Kalman filter, and an algorithm that implements this filter, have been devised for calibrating the focal plane of a telescope. As used here, “calibration” signifies, more specifically, a combination of measurements and calculations directed toward ensuring accuracy in aiming the telescope and determining the locations of objects imaged in various arrays of photodetectors in instruments located on the focal plane. The IPF Kalman filter was originally intended for application to a spaceborne infrared astronomical telescope, but can also be applied to other spaceborne and ground-based telescopes.

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Electronic Absolute Cartesian Autocollimator

Readout is not materially affected by drifts in analog circuitry. An electronic absolute Cartesian autocollimator performs the same basic optical function as does a conventional all-optical or a conventional electronic autocollimator but differs in the nature of its optical target and the manner in which the position of the image of the target is measured. The term “absolute” in the name of this apparatus reflects the nature of the position measurement, which, unlike in a conventional electronic autocollimator, is based absolutely on the position of the image rather than on an assumed proportionality between the position and the levels of processed analog electronic signals. The term “Cartesian” in the name of this apparatus reflects the nature of its optical target.

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Measuring Two Key Parameters of H3 Color Centers in Diamond

These parameters are needed for the further development of diamond lasers.A method of measuring two key parameters of H3 color centers in diamond has been created as part of a continuing effort to develop tunable, continuouswave, visible lasers that would utilize diamond as the lasing medium. (An H3 color center in a diamond crystal lattice comprises two nitrogen atoms substituted for two carbon atoms bonded to a third carbon atom. H3 color centers can be induced artificially; they also occur naturally. If present in sufficient density, they impart a yellow hue.) The method may also be applicable to the corresponding parameters of other candidate lasing media. One of the parameters is the number density of color centers, which is needed for designing an efficient laser. The other parameter is an optical-absorption cross section, which, as explained below, is needed for determining the number density.

Posted in: Physical Sciences, Photonics, Briefs

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Networked Equipment Makes Spherical and Aspheric Optics Manufacturing Predictable

Optical component production becomes more stable and predictable when metrology results inform the manufacturing process. In their quest for the twin grails of high production volume and extreme precision in the manufacture of both spherical and aspherical optical surfaces, manufacturers have been stymied by the difficulty of translating measurement results obtained from metrology tools to adjustments of grinding and polishing processes. In the past, this process involved manual analysis by highly skilled technical personnel — in other words, error-prone humans.

Posted in: Physical Sciences, Photonics, Briefs

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Power Meter Design Minimizes Fiber Power Measurement Inaccuracies

Integrating cavity design minimizes variability caused by fiber positioning, connector orientation, and polarization.Manufacturers of multiplexers, attenuators, amplifiers, and other fiber-optic components must characterize their products for parameters such as insertion loss and polarization-dependent loss. Insertion loss is usually accomplished by measuring output power variations before and after the component has been connected to a laser source. Polarization-dependent loss is measured by varying the input polarization to the device, and measuring the variation in power as the polarization vector is swept through all possible angles. The power meter used to perform these measurements may be sensitive to these types of variations, compromising measurement accuracy of the component under test. Most power meters, for instance, are sensitive to changes in polarization as well as uniformity of illumination of the detector surface and position of the fiber end with respect to the detector. In practice, integrating spheres are used to reduce these sensitivities.

Posted in: Physical Sciences, Photonics, Briefs

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Infrared Emitter Combines Photonic Crystal Technology With MEMS Manufacturing

Microelectromechanical system (MEMS) machining enables infrared emitters to be built directly on a silicon chip.In one of the first real-world applications of photonic crystals, two companies partnered to produce a photonic crystal enhanced (PCE) micro-hotplate device with applications in areas from military combat identification to commercial and biomedical gas sensing technology. Ion Optics, which manufactures optical-based MEMS gas detection sensors and wavelength-tuned infrared emitters, partnered with IMT, which produced the device using its MEMS prototyping and production capabilities.

Posted in: Physical Sciences, Photonics, Briefs

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