Measurements in the Long Wave-Length Infrared from 20μ to 135μ

Abstract

The technique employed in this spectral region is discussed, special emphasis being placed upon the problem of the elimination of shorter wave-lengths. New measurements from 20\ensuremath{\mu} to 135\ensuremath{\mu}, which show the transmission of 11 of the substances most commonly used in the infrared, are presented and discussed. In the light of new absorptions found in crystalline quartz, the reststrahlen measurements from Rubens are discussed. The transmission of sulphur was measured, and between 20\ensuremath{\mu} and 135\ensuremath{\mu}, 8 absorption bands were located. These are compared with the Raman effect measurements of Krishnamurti. The question of an ideal substance for coating receiving elements in the far infrared is also treated.