Photoacoustic figure of merit for photothermal energy conversion efficiency

The photoacoustic signal detected near the non-illuminated back surface of a photothermal converter can be used for comparative studies of the conversion efficiency of the converter. The signal is caused not only by the thermal wave transmitted through the sample, but also by mechanical vibrations of the sample itself. While no absolute absorptance or emittance values can be obtained, the signal reflects the influences of both these quantities on the conversion efficiency. Thus this kind of method may lend itself to quality control of such converters, although direct comparisons between absorbing surfaces on different substrates are still problematic.