Microscopic theory of photoacoustic pulse generation

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Abstract
Nonlinear-response theory to quadratic order in the external electric field is used to derive correlation-function expressions for the hydrodynamic disturbances caused by the absorption of light in linear spectroscopy. For relatively low-frequency sound, this treatment is shown to give the phenomenological expression for the pressure generated by adiabatic expansion of the solvent. In addition, two new terms are obtained. These represent the direct coupling between the dynamics of the absorbers and the local microscopic stress. One of these terms has a dependence on the polarization of the incident light which is totally absent in the phenomenological theory. A photoacoustic experiment is suggested which can measure this new effect.