Optical properties and thermal response of copper films induced by ultrashort-pulsed lasers

A critical point model with three Lorentzian terms for interband transition was proposed to describe temperature-dependent reflectivity (R) and absorption coefficient (alpha) for copper irradiated by ultrashort-pulsed lasers of wavelength 200-1000 nm. After validated with experimental data at room temperature, it was incorporated into a two-temperature model to study ultrafast laser-material interactions. The dynamic changes of optical properties R and alpha, distributions of laser heat density, electron and lattice temperature, and phase changes of a copper film were investigated. Comparing with the experimental data of average absorption showed that the proposed two-temperature model together with the critical point model can simulate satisfying results for temperature-dependent R and alpha. The drastic changes in R and alpha could alter laser energy deposition in a heated target, leading to different thermal responses than those predicted with constant R and alpha at room temperature. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3662897]