Abstract

Photoacoustic spectroscopy is now widely used for detection and analysis of various materials in solid, liquid, or gas phase. Its high sensitivity permits us to detect as low as a few ppb in gases. Relaxation studies in gases are now easily performed with photoacoustic techniques. Quantitative measurement of very low concentration of solid particulates is more difficult. Heat conduction between sample and backing becomes an important parameter, depending on the experimental conditions. Detection of asbestos fibers are presented. More recently, we investigated the measurement of bulk and surface (or interface) absorptions in optical thin-film coatings and highly transparent materials where very low absorption (al < 10^-7) is often met. In infrared analysis, photoacoustic spectroscopy used with FTIR offers a very sensitive and attractive tool. Even heterogeneous or opaque materials may now be analyzed in their natural state. Theoretical studies for heterogeneous materials have been made of the well-known photoacoustic saturation and the contribution of sample dilatation in the photoacoustic signal which becomes important in porous media. Data treatment has been developed and quantitative analysis is possible. Moreover, we can distinguish between the spectrum obtained from the surface species and the spectrum obtained from the bulk material. Experimental results are presented.

© 1985 Optical Society of America