A computer simulation method for studying the ablation of polymer surfaces by ultraviolet laser radiation

Abstract

A computer algorithm designed to simulate the ablation of polymer surfaces by ultraviolet laser radiation is presented. The method is based on a synthesis of the dressed state picture of radiation-matter interactions and a semiclassical ‘‘surface hopping’’ technique. A primary feature of the algorithm is that the intrinsically quantum mechanical process of ultraviolet photon absorption can be simulated while classical molecular dynamics techniques are simultaneously employed to integrate the equations of motion for the nuclear positions and momenta of the polymers. Illustrative results obtained from the algorithm are presented for the ablation of a model polymer surface. Quite different energy redistribution behavior is observed for electronic excitations to a repulsive electronic potential energy surface versus excitations to surfaces that have the possibility of bound vibrational motion. These results suggest that the postulated ‘‘direct’’ photochemical (bond-breaking) ablation mechanism for 193 nm lasers may be dynamically distinct from thermal ablation processes that result from intense local heating of the material by longer wavelength lasers.