High accuracy linear displacement interferometer with probe

Details High accuracy linear displacement interferometer with probe High accuracy linear displacement interferometer with probe

1991-01-02

1992-07-28

McGraw, Vincent P.

Optics: measuring and testing

By particle light scattering

With photocell detection

356358, G01B 902

Patent

active

051335999

ABSTRACT:
A high accuracy linear displacement interferometer capable of measuring changes in displacement of two plane mirror surfaces (60, 61) comprises a source (10) of an input beam (12) with two linear orthogonally polarized components which may or may not be of the same optical frequency, a birefringent optical element (40) and a quarter-wave phase retardation plate (42) for converting the input beam (12) into two separated, parallel, oppositely handed circularly polarized beams (16, 17); a first plane mirror (60) comprising one of the two (60, 61) plane mirror surfaces; a second plane mirror (61) nominally parallel to and rigidly connected to the first plane mirror (60) surface comprising the other of the two plane mirror surfaces; the birefringent optical element (40), the quarter-wave phase retardation plate (42), a right angle prism (48) with reflective, orthogonal faces, and a pair of retroreflectors (44, 45) causing each of the separated, parallel, oppositely handed circularly polarized output beams (32, 33); the quarter-wave phase retardation plate (42) and the birefringent optical element (44) converting the two separated, parallel, oppositely handed circularly polarized output beams (32, 33) into a single output beam (52) in which the phase difference between the two orthogonally polarized components of the single output beam (52) is directly proportional to the linear displacement of the two plane mirrors (60, 61); a polarizer (70) for mixing the orthogonal components of the single output beam (52); a photoelectric detector (83), for producing an electrical measurement signal; means to extract the phase difference from the electrical measurement signal (85), the extracted phase difference being proportional to the optical path length changes between the two plane mirrors (60, 61); and a probe (62) mounted symmetrically in the right angle prism (48).

REFERENCES:
patent: 4334778 (1982-06-01), Pardue et al.
patent: 4577968 (1986-03-01), Makosch
patent: 4950078 (1990-08-01), Sommargren

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