Optics: measuring and testing – By polarized light examination – With birefringent element
Patent
1996-08-20
1998-11-17
Font, Frank G.
Optics: measuring and testing
By polarized light examination
With birefringent element
356358, 356349, 356351, G01B 902
Patent
active
058384855
ABSTRACT:
A method and apparatus for measuring fluctuations in the refractive index of a gas, such as air, in a measurement path (66) may be used to measure displacement of an object (67) independent of these fluctuations. A coherent source of light (1,4) provides two source light beams (11, 12) having source wavelengths (.lambda..sub.1, .lambda..sub.2) along the measurement path (66) which are substantially harmonically related to each other. The beams (11, 12) are electronically processed (98, 981, 982, 983, 984, 985) to provide modified heterodyne phase shifts based on the provided source wavelengths which are similarly harmonically related to the harmonically related source wavelengths for providing a superheterodyne modulation phase substantially insensitive to motion along the measurement path (66).
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de Groot Peter
Hill Henry A.
Caufield Francis J.
Font Frank G.
Merlino Amanda
Zygo Corporation
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