Viscous flow and ablation pressure phenomena in nanosecond UV laser irradiation of polymers

Acceleration and expulsion of a laser-induced melt layer in laser ablation of polymers is studied based on a combination of a quantitative theoretical modeling of ablation pressure and viscous melt flow with an experimental technique of a precise nanoscale measurement of the resulting surface profile. For two particular examples corresponding to so-called 'stationary' and 'non-stationary' liquid layer flows the following results are obtained: (i) the kinematic viscosity of the laser-induced melt layer on the surface of poly(ethylene terephthalate) at extreme conditions of KrF laser ablation is found for the first time and (ii) a new form of material removal in laser ablation is explained - expulsion of long (up to 1 mm) nanofibers with a radius of about 150-200 nm when a poly(methyl methacrylate) target is irradiated with a single pulse of a KrF excimer laser.