Surface temperature measurements on picosecond time scales using surface second-harmonic generation

Abstract

Phenomena involving laser-materials interactions are playing an increasingly important role in a number of disciplines. To understand laser-induced surface processes, it is essential to know both the actual surface temperature increase and the time scales required for thermalization of the deposited energy. We have measured the time-resolved transient surface temperature rise induced by a sub-nanosecond laser pulse incident on a Cu(110) surface in UHV by using surface second-harmonic generation (SHG). Transient surface heating was induced by a 1064 nm infrared pulse having a temporal width of ~100 ps. An amplified dye laser operating near 600 nm with a 6 ps pulse width was used as the SHG probe. The non-resonant SHG signal was found to decrease rapidly as the surface temperature was increased by resistive heating. The physical origins of this decrease will be discussed. The strong SH temperature dependence was used to convert the time-resolved decrease in the SH intensity observed with the infrared heating pulse into a surface temperature profile showing a maximum surface temperature rise of ~50°C. The observed transient surface temperature increase will be compared to calculations using both an equilibrium one-dimensional heat diffusion model and a model that accounts for a hot-electron distribution that is not in equilibrium with the lattice.