Quantitative study of a photoacoustic system for powdered samples

Abstract

The absorption edge of powdered amorphous As2S3 of average particle size 0.0066 cm is explored by the photoacoustic method. The output signal varies significantly with changes in the absorption coefficient β of As2S3 over a range of β from less than 10 cm−1 to more than 104 cm−1, at a chopping frequency of 510 Hz. The saturation behavior of the system at the upper end of this range of β, where both optical and thermal penetration depths are less than the particle diameter, is well approximated by the theory of Rosencwaig and Gersho for homogeneous samples. The behavior for small β is explained in terms of Melamed’s analysis of diffuse reflection and absorption by a powder. The behavior of the photoacoustic cell in the limiting case of a charcoal sample, and the absolute sensitivity, are also investigated and related to theory.