The technique for measuring changes in diffuse surfaces using Electronic Speckle Pattern Interferometry (ESPI) is well known. We present a new electronic speckle pattern interferometer that takes advantage of a single-frame spatial phase-shifting technique to significantly reduce sensitivity to vibration and enable complete data acquisition in a single laser pulse. The interferometer was specifically designed to measure the stability of the James Webb Space Telescope (JWST) backplane. During each measurement the laser is pulsed once and four phase-shifted interferograms are captured in a single image. The signal is integrated over the 9ns pulse which is over six orders of magnitude shorter than the acquisition time for conventional interferometers. Consequently, the measurements do not suffer from the fringe contrast reduction and measurement errors that plague temporal phase-shifting interferometers in the presence of vibration. This paper will discuss the basic operating principle of the interferometer, analyze its performance and show some interesting measurements.
A method for reducing the coherent noise, by a factor of two, in dynamic interferometry measurements is presented. Reducing coherent noise is particularly important in "on-machine" metrology applications where residual noise can be polished into the surface under test. Both theory and experimental measurements are discussed.
A compact, vibration insensitive interferometer design that is well suited for measuring optics while mounted in-situ on polishing equipment is presented. The system employs a single frame phase sensor that permits acquisition in tens of microseconds to mitigate the effects of vibration or relative motion with the test part. The theory of operation is presented along with experimental test results, which characterize repeatability and precision under static and highvibration conditions.
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