Thermal Analysis of Thin Films Under Pulsed Laser Irradiation

A two-dimensional finite-difference method was developed to study the thermal behavior of thin films, irradiated by a pulsed Gaussian laser beam. In particular, the method was applied to rare earth-transition metal alloy films for magnetooptical recording. The effects of the film parameters (thermal conductivity, specific heat, absorption coefficient and film thickness) and the laser parameters (output power, pulse width and beam size) on the heating and cooling behavior were extensively investigated. It was found that the temperature profile of a film was sensitively dependent on those parameters. The results might be utilized to predict the recorded bit size and also to optimize the laser parameters. For a given energy density of a laser beam, a large output power with a short pulse width was desirable for effective heating of a film. It was also found that heating by radial thermal diffusion became important with increasing thermal conductivity of a film. Therefore, to achieve high storage density, a film is required to have low thermal conductivity.