Measurement of thermal diffusivity and conductivity of thin films using laser-line lock-in thermography

Laser-line lock-in thermography consists in illuminating the sample surface with a modulated and focused laser beam and recording the spatial distribution of the temperature oscillations with an infrared camera. In this work we show that it is possible to measure the thermal diffusivity and conductivity of thin films. When the sample is in vacuum, both amplitude and phase of the temperature oscillations behave as a linear functions of the distance to the center of the illumination, and the thermal diffusivity can be obtained from their slopes. When the thin film is surrounded by air, the linearity of amplitude and phase is lost due to the influence of heat conduction to the air. In this case, the thermal conductivity of the material can be obtained by fitting the complete theoretical model (which includes all the heat transfer mechanisms) to the recorded experimental temperature profiles. Validation is performed on two thin films of different thermal transport properties.