Optimised method of thermal diffusivity determination of thin films by means of laser-induced dynamic gratings

Abstract

The transient thermal grating (TTG) technique in transmitting geometry has been applied to the characterisation of thin-film thermal diffusivity. The thermal grating is initially formed in a film surrounded by two substrates The theoretical background and experimental data for diffraction active and nonactive substrates are described. A one-dimensional model of heat diffusion in a three-layer structure fits the experimental data of TTG decay well if the film thickness is less than the thermal grating period. In addition, film thickness, light absorption coefficient in a film, and thermal properties of substrates influence the TTG relaxation time. The optimum experimental conditions have been selected, and the method of thermal diffusivity characterisation of thin films has been devised.