LASER-HEATING OF A 2-LAYER SYSTEM WITH TEMPERATURE-DEPENDENT FRONT SURFACE ABSORPTANCE

Laser heating of a two-layer system is studied and the temperature dependence of the optical absorptance of the irradiated target is considered. The Laplace integral method is used to solve the heating problem. Expressions for the temperature profiles in the thin film and the substrate are obtained. Such profiles, together with the surface temperature are computed for four two-layer systems: aluminum-glass, silver-glass, copper-glass and gold-glass. Each target is subjected at the front surface to incident laser irradiance q(0) of value 10(12) W m(-2). The thickness of the metallic film in each system is 5 mu m. The critical time t(m) required to initiate melting for the four systems considered is computed and compared with the case when the absorptance is constant. Lower values of t(m) are obtained when considering such an effect. For constant absorptance, computations revealed that t(m)=0.0673,2.1312,1.8657 and 1.7440 mu s while for temperature-dependent absorptance t(m)=0.0453,1.1085,1.0108 and 1.0203 mu s for the four elements considered respectively.