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Photothermal thermoelastic bending depends on an optically generated dynamic thermal field distribution within a sample. A generalized description of the distribution is proposed, including the effects of a finite heat propagation velocity and a finite, non-zero time of thermal relaxation (known as thermal memory effects in generalized heat conduction theory), and finally the generated thermoelastic bending is calculated by using both a thin solid-plate approximation and a decoupling system of thermoelastic equations. The comparison between this model and the classical one, which does not account for thermal memory influence, has been made. If the sample is thicker than the value of its minimal thermal diffusion length, the difference between the two models becomes insignificant. Otherwise, it has been shown that the two models tend to overlap at low and high modulation frequencies of the excitation light, while in the mid-frequency range, some deviations become more apparent and thermal memory properties of the sample must be taken into account. The suggested model enables evaluation of thermal memory properties for such a solid.M. Nesic (B) · S. Galovic · M. Popovic

In this paper, a self-consistent inverse procedure is developed for the estimation of linear thermal expansion coefficient and thermal diffusivity of solids from transmission photoacoustic measurement. This procedure consists of two single-parameter fitting processes applied alternately: phase data are fitted by shifting thermal diffusion coefficient, while amplitude data are fitted by shifting thermal expansion coefficient. Each fitting process uses the resulting parameter of the other, previously finished one, thus converging to the best solution-pair achievable. In numerical experiments, the convergence proves to be very fast. The achieved parameter estimation error is as low as 1%, and it can be lowered further more by increasing the fitting resolution in parameter space. The application of the procedure on experimentally obtained aluminum photoacoustic response (measurements) on three thickness levels returns the estimates of its thermal diffusion and thermal expansion coefficients within expected literature boundaries.