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A new thermo-optical method based on the sensitive detection of thermal gradients adjacent to heated sample surfaces is described. Room- and low-temperature experiments were performed using this technique, and its advantages over different methods are discussed.

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Thermal diffusivity measurements of supercooled water have been performed between + 40 °C and - 23 °C, using both optically induced periodic and pulsed heat source in two separate experiments. The resulting temperature field is analysed by monitoring the deflection of a He-Ne laser beam. The thermal conductivity, λ, as deduced from the experiments, decreases continuously with decreasing temperature. The analysis of λ is also discussed both in terms of the classical expression and in terms of a critical law. The influence of the hydrogen bond network structure is discussed, as well. It is verified that the classical relations between λ and the sound velocity, c, are respected, and consequently that the hydrogen bond network structure has the same influence over both λ and c

A theoretical and experimental study of the influence of planar thermal barriers on photothermal reflectance microscopy signals is presented. An analytical solution is developed for the problem of vertical barriers in a semi-infinite solid and the signal contrast obtained when scanning through the barrier is discussed as a function of the thermal resistance, the thermal diffusion length, and the pump and probe beam dimensions. The shape and the width of the signal perturbation introduced by the barrier is also analyzed. For the case of slanted barriers results of finite-element calculations are presented, and the main feature of the signal when going from vertical to slanted barriers is thus shown. Finally, the theoretical predictions are compared with measurements made on Fe sintered samples. Scanning through grain interfaces revealed different signal shapes and contrast. Good agreement between theory and experiment was found when the optical contrast at the interface is negligible. Examples are shown where the thermal barrier model is no longer valid and an extended model seems to be necessary.