Accurate measurements of the thermal diffusivity of thin films and thin filaments using lock-in thermography

In lock-in thermography the 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, in the case of thin samples, the linearity is not found. In this work we identify heat conduction to the surrounding gas as the mechanism responsible for the lost of linearity. Accordingly accurate measurements of the thermal diffusivity require thin samples to be kept in vacuum. Measurements performed in a wide variety of films and filaments confirm the validity of the method.