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) w ere investigated using laser post ionization (193 nm) time-of-flight (TOF) mass spectroscopy. Three regimes of ablation fluence were distinguished wit h respect to detected fragments and differences in their velocity distribut ions. Over the entire fluence range the arrival profiles of the products ma tched 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 puls e by the plume, or to non-thermal effects that may contribute to the ablati on process at high fluences. The dependencies of both die night velocities and the Knudsen layer temperature of the fragments on fluence suggest that PAS ablalion is photothermally driven. However, the excessively high values for average translational energies (up to 34 eV at high fluences) and thei r increases with increasing fragments amu indicate that the process also ha s some non-thermal features.