<title>Measuring Absorption Coefficients In Crystalline Materials</title>

Abstract

Absorption coefficients smaller than 0.001 cm 1 can, with more or less difficulty, be measured by several techniques. All methods can be refined to permit measurement of absorption coefficients as small as 0.00001 cm -1. Spectral data are most readily obtained by transmission (spectrophotometric) methods, using multiple internal reflection to increase effective sample length. Emissivity measurements, requiring extreme care in the elimination of detector noise and stray light, nevertheless afford the most accessible spectral data in the 0.0001-0.00001- 1cm-range. Single-wavelength information is most readily obtained with modifications of laser calorimetry. Thermocouple detection of energy absorbed from a laser beam is convenient, but involves dc amplification techniques and is susceptible to stray-light problems. Photoacoustic detection, using ac methods, tends to diminish errors of these types, but at some expense in experimental complexity. Laser calorimetry has been used for measurements of absorption coefficients as small as 0.000005 cm-1. Both transmission and calorimetric data, taken as functions of intensity, have been used for measurement of nonlinear absorption coefficients.© (1980) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.