Applicability of subpicosecond pulse lasers to determining thermal diffusivity of metals

The transient reflectivity change due to subpicosecond laser-pulse heating is measured for aluminum sheets and a gold film. While hot electron relaxation and/or diffusion seem to control the temperature relaxation in the gold film, the ordinary thermal diffusion seems to be responsible for that in the aluminum sheets. It is possible to determine the characteristic time of the thermal diffusion in the aluminum sheets by fitting a theoretical curve to the observed transient reflectivity. Its reliability is, however, somewhat questionable because of the asymptotic nature of the temporal dependence. Small thermal diffusivity as well as short thermalization time between electrons and phonons is required for the thermal diffusivity to be accurately determined.