Optics: measuring and testing – By particle light scattering – With photocell detection
Patent
1991-12-06
1993-09-28
McGraw, Vincent P.
Optics: measuring and testing
By particle light scattering
With photocell detection
356358, G02B 902
Patent
active
052490300
ABSTRACT:
A pair of orthogonally polarized optical beams that differ in frequency by a constant oscillator-generated reference frequency are directed through and traverse respective fixed and variable length paths of a heterodyne interferometer, following which the beams are mixed and directed to a detector that generates an electrical measurement signal having a phase that varies with changes in the variable path length. Changes in the measurement signal phase are determined by counting cycle-to-cycle phase changes of the reference frequency signal between sampling instants defined by time-spaced occurrences of a known phase of the measurement signal. The resulting count is simultaneously used to determine both changes in length of the variable length path and the elapsed time interval between the sampling instants. Each of the change in path length and and elapsed time interval determinations are accumulated over an extended plurality of sampling instant pairs to provide the current path length and the time of the final measurement of path length change.
REFERENCES:
patent: 4688940 (1987-08-01), Sommargren et al.
Bakach Joseph
Field Alan H.
McGraw Vincent P.
Zygo Corporation
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