Abstract

We developed an analytical model for ultra-short-pulse laser-ablation of solids. In comparison with long-pulse interaction, the distinctive feature of femtosecond pulse interaction is that hydrodynamic motion is suppressed. The exchange of energy between electrons and ions is negligible during the interaction time. In order to achieve ablation, laser intensity has to be increased in inverse proportion to pulse duration. For intensities ~ 10¹³ - 10¹⁴ W/cm² ionisation takes place at the beginning of the laser pulse for practically any target material. Laser energy is absorbed only by free electrons in metals or by stripped electrons in dielectrics. We used a normal skin-effect approach in the analysis of immobile solid-density plasma [1]. The time and space dependence of the electron energy in the skin-layer can be expressed as: here I₀ is the laser intensity; A and l_s, are the absorption coefficient and the skin depth respectively, both are functions of laser frequency ω₀, number density of conductivity electrons n_e, (or plasma frequency ω_pe), electron-ion collision frequency, as well as the angle of incidence and polarisation of the laser beam.

© 2000 IEEE