Modelling of pulsed ultraviolet laser-induced ablation of polymers

Abstract

This paper introduces a theoretical model to calculate the ablation rate induced by a laser pulse on a polymer. The model includes the description of radiation transport processes for the two-photon stepwise absorption of chromophores and the single-photon absorption of the ablation plume. An expression for the etch depth per pulse as a function of incident fluence is derived. The theoretical calculation of the etch depth results is expressed in terms of the effective absorption coefficient of ablation αeff. The behaviour of αeff as a function of incident fluence, applied wavelength, linear, excited state and plume absorption cross sections will be analysed. The results show that the behaviour of αeff is strongly related to the applied incident fluence. At very low applied fluence levels the effective absorption coefficient acquires a value close to the linear absorption coefficient and at high laser fluence levels the contribution of plume absorption plays an important role in the effective absorption coefficient of the ablation process. It will be shown that the theoretical analysis enables us to further our understanding of the nature of the ablation effective absorption coefficient of the novel photopolymer experimental results that have been recently reported in the literature.