Laser Doppler interferometry for measuring small absorption coefficients

Abstract

A laser Doppler interferometric technique for measuring small absorption coefficients of infrared‐transmitting materials is described. The interferometer is calibrated as a remote temperature sensor by monitoring optical path length changes of the sample as a function of temperature. The sample is then irradiated by a CO₂ laser and the change in optical path due to absorbed laser energy is observed interferometrically as a function of time. From this measurement and the calibration data, a temperature‐vs‐time curve is generated from which the absorption coefficient of the sample at 10.6 μ may be calculated.