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

Physical applications of photoacoustic spectroscopy

Theory of Photothermal and Photoacoustic Effects in Condensed Matter

Since the early demonstrations of our concept of pulsed microwave catalysis in chemistry, we have witnessed the coming of age of the technique as an enabling technology in the industrial world, despite the inadequate understanding of the basic mechanisms of how microwaves interact with metallic surface sites and the subsequent energy transfer. We shall present here some very recent developments of the microwave-induced acoustic technique and its applications to a better understanding of the basic surface heating and energy transfer phenomena in pulsed microwave catalytic systems.

Surface heating and energy transfer in pulsed microwave catalytic systems: A microwave-induced acoustic study

We report the experimentally observed variation of the phase angle φ of the photoacoustic (PA) signal as a function of coupling ‘‘gas column thickness’’ for a one‐dimensional PA cell. The PA signal is excited by a modulated continuous laser beam incident on an opaque solid surface, and the gas column thickness is the distance between the solid surface and the window for the incident laser beam. We show that the observed data can be explained in a PA model (called the extended Rosencwaig–Gersho model) which includes the consideration of a residual volume in the PA cell, together with the consideration of viscous damping of the PA signal at small gas column thickness. The effect of viscosity is visible already for gas column thickness of the order of magnitude of one thermal diffusion length.

Influence of gas viscosity on the photoacoustic signal in gas‐microphone cells

The phase angle φ of a gas‐coupled photoacoustic (PA) signal has been measured as a function of coupling gas column thickness lg for a ‘‘one‐dimensional’’ PA cell. The PA signal is excited by a modulated continuous laser beam incident on an opaque solid surface of silicon. We show that the observed data can be explained in a PA model including the consideration of a residual volume in the PA cell, together with the consideration of viscous damping of the PA signal at small lg.

Y. H. Wong

Papers

Influence of gas viscosity on the photoacoustic signal in gas‐microphone cells

Effect of coupling gas viscosity on the photoacoustic signal