Fluid modeling of the laser ablation depth as a function of the pulse duration for conductors

Abstract

Laser ablation of an aluminum target as a function of the pulse duration, for fluences up to $30{\mathrm{J}/\mathrm{c}\mathrm{m}}^2$ and a wavelength of $0.8\mu \mathrm{m},$ is investigated by means of a fluid code. For a given fluence, the ablation depth shows a minimum for a pulse duration of $\sim 10\mathrm{ps}$ between a maximum obtained for pulses shorter than $\sim 1\mathrm{ps}$ and a lower maximum obtained for pulses in the nanosecond range, in qualitative agreeement with published experimental results. The decrease in ablation depth with increase in pulse duration observed between $1$ and 10 ps results from the reduced temperature rise near the surface due to increased inward heat transport. The increase in the ablation depth above $\sim 10\mathrm{ps}$ is due to the increase in electron density gradient length while the laser pulse intensity is close to maximum, which thus enables the plasma to absorb more of the laser pulse energy for increased ablation.