Modelling of Thin-Film Single and Multi-Layer Nanosecond Pulsed Laser Processing

Abstract

A complete model of nanosecond pulsed laser scribing of arbitrary thin multi-layer structures is presented. The chain of events is separated according to time-scale; an initial simulation considers material response during the pulse; another combines this result with the much slower effects of heat flow away from the laser axis. The former considers heating, vaporisation and phase explosion of metals in the course of a single pulse, accounting for variations in thermal conductivity and optical absorption as the material becomes superheated and approaches its critical temperature. The latter calculates the bidimensional heat flow in a complete multi-layer structure over the course of a scribing operation, combining material properties and considering removal by both short-pulse ablation and long-term heating of the work piece. Simulation results for the single pulse ablation of an aluminium target align well with published experimental data both in terms of phase explosion threshold and ablation depth as a function of fluence. Bidimensional heat flow simulations of a polypropylene–aluminium–polypropylene triplex structure reveal the progression of events towards steady state behaviour; aluminium ejected due to short-pulse ablation and plastic removed due to conduction.