SE330991B - - Google Patents

Abstract

1,233,597. Photo-electric interferometers. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. May 30, 1968 [June 2, 1967], No.25965/68. Heading G1A. [Also in Division G2] In a Michelson interferometer the source produces two coherent beams of slightly different wavelength and different polarization and phaseansiotropic means such as a quarter-wave plate are located in at least one of the partial beams whereby the state of polarization of its radiation when incident upon the beam combiner is orthogonal to its state of polarization when emerging from the beam-splitter. Left and right circularly polarized beams of 1À153Á radiation from a He-Ne laser 1, Fig. 1 having a frequency difference of 0À2 Mc/ s are converted into plane polarized beams 4, 5 by a #/4 plate 3. A beam-splitter 2 comprising alterating layers 8 of different refractive index upon which the beams are incident at the Brewster angle reflects beam 5 to a fixed retroreflector 11, 13 through a #/4 plate 9 and transmits beam 4 to a retroreflector 12, 14 through a #/4 plate 10. The reflected beams 15, 16 are recombined by beamsplitter 2 and pass through a plane polarizer set at 45 degrees to the planes of beams 25, 26 to a detector 18 which has an output at the beat frequency of the beams 25, 26 and phase modulated by the position of retroreflector 12, 14. A detector 18 receiving laser light via beam-splitting mirror 22 and a polarizer 19 produces a reference phase. In another embodiment, Fig. 2, (not shown) the polarizing beam-splitter is replaced by an isotropic beam-splitter and the #/4 plate 9 is omitted. The recombined beam is split by a polarizing beam-splitter and the split beams fall on separate detectors which produce signals at the beat frequency of the source beams and with a phase difference dependent upon the position of the movable retroreflector.