Application of the Photoacoustic Effect for Obtaining Relative Efficiencies of Photothermal Converters

The actual and practical efficiency of a photothermal converter is the ratio of the incident energy and the useful heat that can be extracted. It is determined mainly by the optical and thermal properties of the converter. Ideally, such efficiencies should be determined under conditions that are close to those under which the converter will be used in practice. For selective surfaces the ratio of integrated solar absorptance (α) and integrated emittance (ε) at a specified temperature is often used as a figure of merit. However this method often overestimates the importance of one of these properties1. Therefore calorimetric methods are sometimes preferred, but in many cases they do not lend themselves to use under close to "practical" conditions, and often put severe restrictions on sample size and shape2.