The strong influence of heat losses on the accurate measurement of thermal diffusivity using lock-in thermography

In modulated photothermal experiments the lateral thermal diffusivity can be obtained from the slope of the linear relation between the phase of the surface temperature and the distance to the heating spot. However, this slope is greatly affected by heat losses so that the measured thermal diffusivity is overestimated, especially for thin samples of poor thermal conducting materials. In this paper we definitely identify the physical mechanism responsible for the overestimation of the diffusivity as heat conduction to the surrounding gas. Accurate measurements of the thermal diffusivity using the “slope method” have been obtained by keeping the sample in vacuum.