Abstract

Industrial implementation of femtosecond laser-based micromachining applications requires the characterization of the material response to different levels of laser exposure, ranging from laser damaging evaluation for laser technology purposes to determination of laser ablation characteristics for micromachining processes. The problem of laser damage and ablation measurement in femtosecond regime has been extensively addressed in the literature, with a variety of ex-situ investigations of the morphological changes incurred by the target [1], and in-situ measurements tracking the properties of the created plasma or any change in the optical properties of the studied sample [2]. All these investigations give useful insights on the mechanisms governing the laser–matter interaction in femtosecond regime and important data for the development of laser-based processes. Nevertheless, they are often difficult to confront due to the variety of experimental setups and diagnostics, as well as measurement procedures. To provide valuable information on the effective ionization mechanisms and to progress towards accuracy and predictability of the material response to femtosecond laser irradiation, the precise experimental knowledge and theoretical analysis of both damage and ablation thresholds is essential. To this aim, we perform a simple experiment to precisely evaluate in the same operating conditions the behaviour of the damage and ablation thresholds under the wide excursion of a single experimental interaction parameter, i.e. the laser pulse duration. The experiments are done at 800 nm in single shot regime to avoid any incubation effects. We then measure and model the damage and ablation thresholds at the surface of a well-known dielectric material, e.g. fused silica, using pulses ranging from 7 fs to 300 fs (see Figure 1). The relevant criteria to numerically assess the damage and ablation thresholds are related to the lattice melting temperature T_m and the electronic cohesion temperature T_ec, in accordance with experimental observations.

© 2011 Optical Society of America