Analysis of the temperature dependence of the ratio of intensities of beams transmitted and reflected by a germanium beamsplitter

Plane—parallel optically transparent plates widely used to deflect a part of the beam for the beam intensity measurements or formation of the reference beam in spectrometers and lidars are examined. It is shown that the ratio of intensities of two split-beam components does not remain constant during the entire measurement process. The strong temperature variations of the ratio of intensities of transmitted and reflected beams, formed when splitting NH₃-laser radiation (λ~13 μm) by a 2.7-mm germanium plate with a wedge angle of about 1', are revealed. The mathematical analysis, taking into account not only the temperature dependence of the path-length difference of two rays, one of them passing through the plate two additional times, but also the plate wedging, has provided the explanation of the experimental results.