Contribution of substrate absorption to the formation of the second harmonic of nonlinear photoacoustic response
A theory of the generation of the second harmonic of a nonlinear photoacoustic response has been proposed for the cases when the substrate, along with the sample, is absorbing. The general expression for the complex amplitude of temperature perturbations in the buffer gas is obtained. The case when the sample is thermally thin and transparent is investigated in detail. For this case, expressions are obtained that describe the features of the generated nonlinear PA-signal at the modulation frequency and optical absorption coefficient.