Characterization of laser ablation of polymethylmethacrylate at different laser wavelengths

Abstract

Pulsed laser ablation of polymethylmethacrylate (PMMA) in high vacuum was investigated by using different laser beams. A Nd:Yag laser, working at fundamental (1064 nm) and second harmonics (532 nm) with 9 ns pulse duration and 800 mJ maximum pulse energy was used at INFN-LNS of Catania. Two excimer UV lasers working at 308 nm (XeCl) and 248 nm (KrF) with 20 ns pulse width and 600 mJ maximum pulse energy was used at INFN-LEAS of Lecce. The laser ablation effects on the PMMA were investigated by using similar experimental set-ups and fluences ranging between 2 and 20 J/cm2. A 200 amu mass quadrupole spectrometer was employed to detect ‘on line’ the atom and molecular species emitted in vacuum by the laser ablation process. The ablation yield increases with the laser wavelength, demonstrating that IR radiation induces photothermal effects. The molecular fragmentation increases with the photon energy, demonstrating that photochemical effects become predominant for UV radiation. An investigation about the possible laser ablation mechanisms of PMMA, depending on the laser parameters, will be presented and discussed.