Heating of Metals by Ultra-Short Laser Pulse: Hyperbolic Over Parabolic Considerations

Laser ultra-short pulse heating finds wide applications in electronic and power industries. Since the heating phenomenon is extremely short, experimentation for temperature predictions becomes difficult and expensive. The model studies provide useful information on temperature behavior inside the irradiated material. Since thermal separation of electron and lattice sub-systems, under laser ultra-short pulse, creates nonequilibrium energy transport across sub-systems. Hence, when modelling the thermal transport, consideration of hyperbolic heat equation becomes appropriate than that of the parabolic model due to the finite thermal wave speed. The present study focuses on the temperature response of substrate material (copper) under laser ultra-short pulse heating. The thermal response of the material in the irradiated region is modelled incorporating the hyperbolic thermal and parabolic behavior. Normalized temperature difference between both models was used to assess materials response. The findings revealed that hyperbolic behavior is more pronounced in a depth, below the surface, almost twice the depth of absorption of the laser beam. Electron temperature remains higher than lattice temperature because of absorption of incident laser irradiation, which causes thermal separation of the lattice and electronic sub-systems.