Study of femtosecond pulsed laser heating of bilayer metallic films at various laser angles of incidences and polarizations using the two-temperature model

Abstract

We examine the thermal heating behavior of gold-copper bilayer thin metal targets treated under femtosecond single-pulse laser irradiation using the one-dimensional two-temperature model. A comparison is made between the spatiotemporal evolution of lattice temperatures of gold single layer and gold-copper bilayers. Moreover, the effects of the laser angles of incidence and polarization on the electron and lattice temperatures are studied. Dynamic optical properties are included within the laser source term to effectively describe the oblique angle of incidence configurations with the use of the finite element method. We found that the addition of the copper layer does have a minimal effect on the surface temperature of the gold target. At higher angles of incidence, the surface temperatures of the irradiated targets reduce due to changes in the effective laser beam spot size and fluence. P-polarized laser beams, which have electric fields aligned along the laser beam propagation direction, induce higher temperatures through resonant absorption compared to s-polarized laser beams which have electric fields oscillating along the film surface.