Interferometer with environment sensitive static etalon

Abstract

An interferometer suitable for length measurements, comprising a laser light source, a beam splitter to divide light stemming from the laser light source into a measuring beam and a reference beam, and recombination means at which the reference beam being guided along a reference path and the measuring beam interfere. The measuring beam travels along a measuring path that leads over a movable measuring reflector and partly through a gaseous ambient medium. The interferometer further comprises photodetector means to analyze optical interference signals stemming from the recombination means. At least one static etalon of a known length is provided to determine or compensate for variable environmental conditions (variable refractive index) of the ambient medium. The etalon comprises two reflection surfaces and is illuminated by light stemming from the laser light source. The space lying inbetween these reflection surfaces is filled with the ambient medium. The etalon or etalons is (are) connected to a flexible optical fibre, respectively, the flexible optical fibre conveying light from the laser light source. A precise illumination of the etalon is obtained, and the etalon can be placed near the measuring path in a simple manner.

Dependencies are inferred from the claim text.