Moire interferometry near the theoretical limit.
The theoretical upper limit of moire interferometry is approached as the reference grating pitch approaches lambda/2 and its frequency approaches 2/lambda. This work demonstrates the method at 97.6% of the theoretical limit. A virtual reference grating of 4000 lines/mm (101,600 lines/in.) was used in conjunction with a phase type reflection grating of half of that frequency on the specimen. Sensitivity was 0.25 microm/fringe (9.8 microin./fringe). In-plane displacement fringes of excellent definition were obtained throughout the 76 x 51-mm (3 x 2-in.) field of view. They were very closely packed, exhibiting a maximum fringe density of 24 fringes/mm (610 fringes/in.). Effectiveness of moire interferometry near the theoretical limit was proved.
Weissman
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EM
Virginia Polytechnic Institute & State University, Department of Engineering Science & Mechanics, Blacksburg, Virginia 24061, USA.
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