Entropy analysis in relation to laser shortpulse heating of silver

Laser shortpulse heating triggers non-equilibrium energy transport in the surface region of the metallic substrate. In this case, volumetric entropy generation is governed by the non-equilibrium energy transport due to coupling of electron and lattice subsystems as well as thermomechanical coupling in the lattice system. In the present study, non-equilibrium energy transport inside the metallic substrate is modelled using an electron kinetic theory approach. Volumetric entropy generation inside the substrate material during non-equilibrium energy transport is formulated. The effect of thermomechanical coupling on the energy transport is included in the analysis. Temperature and volumetric entropy profiles are computed for silver. It is found that an electron temperature well in excess of lattice site temperatures occurs in the surface vicinity of the substrate material. Volumetric entropy generation due to electron-lattice coupling dominates the other sources of entropy generation. Thermomechanical coupling has no significant effect on the volumetric entropy generation due to a small thermal displacement of the irradiated surface, which is in the order of 10^-10 m at the centre of the irradiated spot.