Time-resolved studies of electron-phonon relaxation in metals using a free-electron laser

Here we report recent experiments on ion emission from metals (Ti, Nb, Mg) using a free-electron laser that delivers a train of subpicosecond micropul ses in the mid-infrared (IR). The laser intensities for the surface damage and ion emission thresholds are used as markers for the onset of energy tra nsfer to the lattice for ablation. Numerical calculations based on the Anis imov two-temperature model are used to evaluate the electron temperature T- e and the lattice temperature T-i. The results are discussed in terms of th e Hertz-Knudsen equation for vaporization and a model based on laser-induce d multiple electronic transitions. (C) 2000 Elsevier Science B.V. All right s reserved.