GB1197212A - Interferometer - Google Patents

Abstract

1,197,212. Photo-electric interferometers. PERKIN-ELMER CORP. July 18, 1967 [July 18, 1966; June 7, 1967], No. 32911/67. Heading G1A. [Also in Divisions G4-6] An interferometer for indicating changes in length of an optical path comprises means for transmitting a first beam of light of predetermined polarization along the optical path and combining the transmitted beam with a second beam orthogonally polarized relative to the first to produce a plane polarized beam, the plane of which varies with variations in the optical path. Light from a laser 10, Fig. 1 is collimated by lenses 16, 18 and rendered circularly polarized by a quarter wave plate 20. The light beam is split by a half silvered surface 24 and one half is transmitted to a retro-reflector 14 mounted on the bed 26 of a machine tool. The polarization of the reflected light is reversed by the reflector 14 so that when it is combined with the other half of the split beam at the half silvered surface 28 a plane polarized beam results with plane dependent upon the position of reflector 14. The plane polarized beam is split by a half silvered surface 33 and passes to photocells 36, 38 through polarizers 32, 34 with their planes at 45 degrees. The two-phase signal produced by clippers 40, 42 drives a counter 44. The interference fringes may be viewed on a monitor 29. In a modification, Fig. 5 (not shown) the surfaces 24, 28 are of dielectric material. The beams transmitted and reflected by the surface 24 are then orthogonally elliptically polarized and recorders are inserted between the beam-splitters 27, 30 to produce the plane polarized output beam Ires. In another embodiment, Fig. 3 the beam Ires is focussed on a single photo-cell 36 through a birefringent plate 52 energized from an A. C. generator 54 so that the axis of the plate effectively rotates. The frequency of this rotation adds to frequency with which the plane of polarization of Ires rotates and this latter frequency is derived by feeding the photo-cell output and a reference signal from the generator 54 to the forwards and backwards inputs respectively of a bidirectional counter 44. In a modification, Fig. 4, (not shown) the photo-cell output is fed to a frequency measuring circuit to give an analogue indication of the velocity of the reflector 14.