Low Optical Absorption Measurement of Leser Materials Using Interferometric Calorimetry

Abstract

Laser optical components must exibit a much lower absorption coefficient than normal optical components. Especially, a high power laser system requires very low loss materials because the heat produced by absorbed light causes deformation or damage. The progress in the technique of the small absorption coefficient measurement has contributed to the development of low loss materials. As the surface damage threshold is in certain cases lower than the bulk damage threshold, it is necessary to separate the surface absorption coefficient from the bulk absorption coefficient. The sensitivity of laser calorimetry, which measures the temperature rize of the sample, is directly proportional to laser power. Interferometric laser calorimetry uses an interferometer to measure the optical path length change caused by the temperature rize. This method has the merit of quantitativeness and high sensitivity in separating surface absorption from bulk absorption. We measured absorption coefficients of optical materials; quartz, CaF₂ and KCl, and the results are reported.