The photoacoustic effect in liquids and solids has been experimentally investigated using light from helium-neon and argon-ion lasers. In an effort to evaluate the theoretical explanation of the effect (see preceding paper), the photoacoustic amplitude Q has been measured as a function of chopping frequency f for several liquids and solids with large values of the optical absorption coefficient β. The experimental results compare favorably with theoretical predictions over wide ranges of f and β. Water solutions with varying concentrations of a common pH indicator were prepared to obtain a controlled evaluation of Q(f,β). It was found that curve fitting the theory to the experimentally determined graph of Q vs f permits the determination of β to at least two significant figures for a solute in water with a β range of at least 50–5000 cm−1. This result indicates that the photoacoustic effect provides an important technique for determining the absolute optical absorption coefficient in highly absorbing liquids and solids.
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Wetsel et al. (1976) studied this question.