TRANSIENT THERMAL GRATINGS AT SURFACES FOR THERMAL CHARACTERIZATION OF BULK MATERIALS AND THIN-FILMS

Transient Thermal Gratings (TTGs) at surfaces of absorbing materials h ave been utilized for investigating heat diffusion in bulk materials a nd thin films. In this report, we describe the theoretical background of the technique and present experimental data. TTGs were excited in t he surface plane by interference of two pulsed laser beams and monitor ed by a cw probe beam, either via temperature dependence of the reflec tivity or by deflection from the displacement pattern. A theoretical m odel describing the thermal and thermoelastic surface response was dev eloped, both for a homogeneous material and a multilayer structure. Th e potential of the technique will be demonstrated by experimental resu lts on (i) thermal diffusivities of bulk materials, (ii) anisotropic l ateral heat transport, acid (iii) thermal diffusivities of metal and d iamond films. Furthermore, we will show that TTGs allow thermal depth profiling of inhomogeneous materials whenever there is a vertical grad ient in thermal conductivity.