Testing optical surfaces by the method of the caustic using a phase-stripe as spatial filter.
The use of a phase stripe as spatial filter in the measurement of optical surfaces by the method of the caustic was studied. This is an adaptation of Zernike's phase contrast method to the zonal measurement of optical surfaces by the method of the caustic. We analyzed three path differences introduced by the stripe lambda/4, lambda/3, and lambda/2. The best results may be expected for lambda/3, and with a phase stripe of this path difference a mirror was tested. The mean square deviation between several measurements with this spatial filter was 0.0076lambda.
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de Zenobi
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