Entropy Production During Laser Picosecond Heating of Copper

Abstract

Nonequilibrium energy transport taking place in the surface region of the metallic substrate due to laser short-pulse heating results in entropy production in electron and lattice systems. The entropy analysis gives insight into the irreversible processes taking place in this region during the laser short-pulse heating process. In the present study, entropy production during laser shortpulse heating of copper is considered. Equations governing the nonequilibrium energy transport are derived using an electron kinetic theory approach. The entropy equations due to electron and lattice systems and coupling of these systems are formulated. The governing equations of energy transport and entropy production are solved numerically. Two pulse shapes, namely step input intensity and exponential intensity, are employed in the analysis. It is found that entropy production due to coupling process attains higher values than those produced due to electron and lattice systems. The effect of pulse shape on the entropy production inside the substrate material is significant.