Method and apparatus for two-wavelength interferometry with optical heterodyne processes and use for position or range finding

摘要

An apparatus for measuring changes in a variable interference section of an interferometer comprises a laser source for producing beams of the frequency n.sub.1 and the frequency n.sub.2, polarizing beam splitters for producing cross-polarized partial beams of frequency n.sub. 1 or n.sub. 2, modulators for displacing the frequency of one of the partial beams by frequency f.sub.1 or f.sub.2, a pair of deflecting mirrors in each case and polarizing beam splitters for combining the partial beam n.sub.1, n. sub.1 +f.sub.1, n.sub.2, n.sub.2 +f.sub.2. The apparatus further includes two photodetectors, upstream of which are arranged a polarizer, a Michelson interferometer, a non-polarizing beam splitter for splitting the partial beams in each case into a measuring light beam or a reference light beam. The reference light beam passes to an associated photodetector. The measuring light beam passes into the Michelson interferometer and then to the associated photodetector. The signals of the photodetectors are demodulated according to the amplitude and the phase difference between the two demodulated signals is determined. This phase difference is only dependent on the position of a measurement object and the equivalent wavelength of the difference n.sub. 1 -n.sub.2. A method for measuring changes by determining positions or distances is performed by the apparatus.