GB1345204A - Interferometer systems for sensing the idsplacement of an object - Google Patents

Abstract

1345204 Photo-electric interferometers THOMSON-CSF 19 April 1971 [13 March 1970] 24003/71 Heading G4H [Also in Division G1] An interferometer in which photo-electric detector means is used to produce interlaced waveforms representative of the displacement of the movable mirror, a #/8 plate is used to produce splitting into two beams of polarized light from a coherent source. In an arrangement for providing two interlaced waveforms, Fig. 1, a coherent light source La, e.g. a laser and polarizer P provide a beam polarized in a direction parallel to the bisector of the axes of elliptical polarization of birefringent, #/8 plate B. The action of the plate B is such as to produce beams I 1 , I 2 , passing semireflective plate L, which are phase separated by #/2 and interfere individually with the beam I 01 reflected from movable mirror MM to produce two fringe systems. The interfering light is analysed by a detection arrangement comprising semireflector L 1 and a pair of analyser/photodetector arrangements. The analysers are respectively parallel to the directions of polarisation of the beams I 1 , I 2 i.e. parallel to the axes of the plate B. Four interlaced waveforms may be provided from the outputs S 1 , S 2 of the detectors r 1 , r 2 by the use of summation and inversion circuits, Fig. 5 (not shown), to obtain the sum and difference of s 1 and s 2 besides using s 1 and s 2 themselves. An optical method of obtaining four interlaced waveforms, Fig. 3 (not shown) involves the use of three semireflectors and four analyser photodetector arrangements the analysers being angled respectively at -22À5 degrees, +22À5 degrees, +67À5 degrees and +112À5 degrees with respect to the X-axis of the plate B.