Marica N. Popović

Theory of photoacoustic effect in media with thermal memory

This paper presents a model for indirect photoacoustic response that includes thermal memory effects. At low frequencies, the model reduces to the well-known thermal piston model of photoacoustic response given by Rosencweig and Gersho. However, at high frequencies, the presented model predicts resonant behavior of amplitudes and phases of photoacoustic response and determines the respective resonant frequencies. The results of the presented model enable experimental determination of standard thermal properties of solids (thermal diffusivity and thermal conductivity), as well as thermal memory properties, thermal relaxation time, and heat propagation speed.

Thermal memory influence on the thermoconducting component of indirect photoacoustic response

In this paper, a model of the thermoconducting component of the indirect photoacoustic (PA) response is derived that includes thermal memory properties of the examined material and its fluid environment. A comparison is made between the derived model and the classic one, which neglects the influence of thermal memory. It has been shown that, at modulation frequencies lower than a certain boundary frequency of the light source, these models tend to overlap, while at higher frequencies, noticeable differences occur. The boundary frequency depends on heat propagation velocity through the sample and its thickness. This observation limits the validity domain of previous models to a range lower than the boundary frequency, offering, at the same time, the possibility of obtaining thermal memory properties using PA effects at frequencies above it.