Photochemical and Photothermal Model for Pulsed-Laser Ablation

A model of the interaction of UV laser pulses with organic polymers is presented. The three distinct features of this model are as follows: 1 ) It combines photochemical and photothermal processes for breaking bonds. 2 ) It tracks the percentage of bonds broken where the higher dissociative states are not allowed to relax back to the lower states. 3 ) The model does not need an experimentally inferred value of threshold e uence to determine the onset of ablation. The mathematical model presented here is based on the system of a two-photon absorption model, where sets of rate equations that include radiative transport and energy absorption are solved. Solutions of this model are discussed, and the results are shown to compare well with experimental etch depth vs e uence curves from the literature for a wide range of pulse widths from 7 to 300 ns. Parametric results are also presented for 193- and 308-nm UV laser wavelengths for different laser and polymer parameters. The dependence of the temperatures and ablation depths for different laser e uences and widths of the laser pulses are obtained.