This paper reviews the theory and applications of photoacoustic (also called optoacoustic) methods belonging to the more general area of photothermal measurement techniques. The theory covers excitation of gaseous or condensed samples with modulated continuous light beams or pulsed light beams. The applications of photoacoustic methods include spectroscopy, monitoring deexcitation processes, probing physical properties of materials, and generating mechanical motions. Several other related photothermal methods, as well as particle-acoustics and wave-acoustics methods are also described. This review complements an earlier and narrower review [Rev. Mod. Phys. 53, 517 (1981)] that is mainly concerned with sensitive detection by pulsed photoacoustic spectroscopy in condensed matter.

Applications of photoacoustic sensing techniques

Photoacoustic and related photothermal techniques

A minimal‐volume photoacoustic cell method is demonstrated for obtaining the thermal diffusivity of solids. It is based on the measurement of the acoustic signal as a function of the modulation frequency in the region where the sample is thermally thick. The method is tested by using metal, semiconductor, and polymer samples.

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Minimal‐volume photoacoustic cell measurement of thermal diffusivity: Effect of the thermoelastic sample bending

A quantitative analysis of the electronic deformation (electronic strain) contribution to the photoacoustic signal in semiconductor samples was done. The photoacoustic (PA) effect was investigated as a function of the modulation frequency in a transmission detection configuration. The theoretical model for this configuration was given for the thermal and elastic processes besides the carrier transport characteristic and the relation for electronic elastic deformation was derived by the theory of the elastic thin plate vibrations. Analysis showed that the electronic deformation mechanisms can have an important infleucne on the PA signal in the frequency range typical for gas-microphone detection. The experimental photoacoustic data for Si samples were measured and they exhibited a satisfactory agreement with the theoretical model.

Photoacoustic frequency transmission technique: Electronic deformation mechanism in semiconductors

The system of partially coupled plasma, thermal, and elastic wave equations and conditions for neglecting the coupling between them is analyzed. The treatment considers a semiconductor elastic medium with isotropic and homogeneous thermal and elastic properties. The solution of the coupled system of plasma, thermal and elastic equations is a very complex problem. In most practical cases partially coupled treatment is sufficient. Conditions where it is possible to neglect the coupling between the plasma, thermal, and elastic waves are considered in this work. Special cases for coupled thermal and elastic waves (the thermoelastic problem) and coupled plasma and elastic waves (the electronic deformation) are taken into consideration. An approximate quantitative analysis of the coupling effects is given.

Plasma, thermal, and elastic waves in semiconductors

In some photoacoustic experiments, thermoelastic bendings of solid samples produce strong signals which cannot be analyzed by usual photoacoustic calculations. We propose a model that, using the thermoelastic equations, analytically explains the effect of this bending. It is found that the model agrees well with data obtained from an experiment sensitive to thermoelastic deformations only. Furthermore, the model is also consistent with previous piezoelectric‐photoacoustic calculations. This experiment also leads to measurements of thermal diffusivities.

Influence of thermoelastic bending on photoacoustic experiments related to measurements of thermal diffusivity of metals

This paper sets forth a self‐contained theoretical description of the photoacoustic effect in a thick powdered or porous sample at low modulation frequencies where the sample medium can be considered homogeneous from the point of view of heat diffusion. It is shown that the photoacoustic signal results from two contributions: the heat flux from the sample to the gas plus the expansion of the interstitial gas and that the pressure is essentially uniform throughout the sample. Scattering effects are introduced with a Kubelka–Munk modified model and an expression is first given for the conventional partially filled cell. We discuss of these results and their application to the explanation of several texture effects and to the analysis of experimental data. Using a sample composed of chrysotile asbestos powder, we present experimental data and perform an approximate analysis to retrieve the absorption spectrum. Several experimental results are also presented and thoroughly discussed for a cell completely fill...

F. Lepoutre

Papers

Influence of thermoelastic bending on photoacoustic experiments related to measurements of thermal diffusivity of metals

Photoacoustic spectroscopy of thick powdered or porous samples at low frequency