A Laser Ionization Time-of-Flight Mass Spectrometric Study of UV Laser Ablation of Polyarylsulfone Films.

Neutral fragments from the 248 nm laser ablation of polyarylsulfone (PAS) were investigated using laser post ionization (193 nm) time-of-flight (TOF) mass spectroscopy. Three regimes of ablation fluence were distinguished with respect to detected fragments and differences in their velocity distributions. Over the entire fluence range the arrival profiles of the products matched with a shifted Maxwell-Boltzmann distribution. Interestingly, average translational velocities revealed a non-monotonical dependency on ablation fluence. This is probably be due to screening effects of the ablation pulse by the plume, or to non-thermal effects that may contribute to the ablation process at high fluences. The dependencies of both the flight velocities and the Knudsen layer temperature of the fragments on fluence suggest that PAS ablation is photothermally driven. However, the excessively high values for average translational energies (up to 34 eV at high fluences) and their increases with increasing fragments amu indicate that the process also has some non-thermal features.