Time evolution of reflective thermal lenses and measurement of thermal diffusivity in bulk solids

A simple method for optically measuring the thermal diffusivity of solids is demonstrated. The thermal displacement created on a substrate by a focused laser beam is determined from the divergence that it induces in a weak probe beam. The dynamics of the surface lens and the amplitude of the probe beam's divergence are then used to determine the thermal diffusivity of the substrate. Several materials that span a wide range of thermal properties are studied.