Thermal diffusivity and thickness measurements for solid samples utilising the optoacoustic effect

A simple apparatus is described that permits heat-flow characteristics of a sample to be determined, and its application to the determination of the thermal diffusivity or thickness of polymer films on a copper substrate is reported. The apparatus utilises the optoacoustic effect in which periodically interrupted radiation is absorbed by a solid sample to give rise to a similar periodic variation of the pressure of the air in contact with the sample surface in a closed cell. The amplitude and phase of the observed optoacoustic signal depend on the thermal diffusivity and thickness of the material irradiated.