Optics: measuring and testing – By polarized light examination – With birefringent element
Patent
1996-08-20
1998-06-09
Font, Frank G.
Optics: measuring and testing
By polarized light examination
With birefringent element
356358, 356349, 356351, G01B 902
Patent
active
057643628
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 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. Beams (11, 12) make multiple passes over measurement path (66) where the number of passes for the respective light beams are harmonically related, the relationship of harmonics being substantially the same as said substantially harmonic relationship between the wavelengths to provide heterodyne phase shifts based on the provided source wavelengths and the number of passes over the measurement path (66) for providing a superheterodyne modulation phase substantially insensitive to motion along the measurement path (66).
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de Groot P.
Hill Henry Allen
Caufield Francis J.
Font Frank G.
Merlino Amanda
Zygo Corporation
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