Proceedings PaperMetrology for spatial interferometry II
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Very high resolution spatial interferometry requires picometer level 1D metrology, surface metrology and 3D metrology. Micron level accuracy is required for absolute metrology systems for spacecraft like the proposed Orbiting Stellar Interferometer carrying high resolution spatial interferometers. A surface metrology system with a repeatability of less than 0.1 nm over an aperture of several inches in vacuum has been demonstrated. An absolute calibration system for this gauge is in development. An absolute metrology system with an accuracy of 10 microns over a distance of 10 meters is also under construction. This system uses a 1319 nm, solid-state, infrared laser locked to an Ultra-Low-Expansion glass cavity to an accuracy exceeding 1 part in 1010. The length of the cavity is controlled by a thermal vacuum oven. 1 millidegree Centigrade root-mean-squared (rms) cavity temperature stability with the oven in vacuum has been achieved for time scales of days. The digital laser servo is capable of following the length of the cavity with an Allen deviation of few hundred Hertz for time scales of a day. Two lasers locked to the same cavity are used to supply a simultaneous cavity length measurement as well as the absolute distance measurement. The absolute distance measuring part of the gauge is under construction. An auto alignment system is being developed for our linear relative metrology gauge which had achieved an accuracy of 0.1 picometers. This gauge will be used to construct a 3D metrology gauge with an accuracy of less than 10 pm rms for time scales of minutes initially.