Anomalous behavior of the open cell photoacoustic signal: explanation using a thermal wave interference model

We show that the front open cell photoacoustic signal due to a sample consisting of a glass plate with a metal coated surface, at which thermal waves are generated by periodical light absorption, enhances for certain modulation frequencies when the other glass surface is covered with a liquid sample, contrary to the intuitively expectation based in the assumption that the liquid provides a new channel for heat conduction, thereby decreasing the substrate temperature. Experimental results are shown and the effect is explained using a thermal wave interference model. (Full text)