Contribution of substrate absorption on formation of second harmonic of nonlinear photoacoustic response

A theory for the excitation of second harmonic of nonlinear photoacoustic signal by a single-layer sample, when the substrate, like the sample, is absorbing has been developed. The expression for the temperature fluctuation in the buffer gas has been obtained. The case when the sample is transparent and thermally thin has been studied in detail. The decay regularities of amplitude of excited nonlinear photoacoustic signal from the modulation frequency and the optical absorption coefficient have been revealed. (author)