Dopant induced ablation of poly(methyl methacrylate) at 308 nm

Poly(methyl methacrylate) (PMMA) is highly resistant to laser ablation at 308 nm. Either very high fluences or absorbing dopants must be used to ablate PMMA efficiently at this wavelength. We investigate two dopants, pyrene and a common solvent, chlorobenzene, using time-of-flight mass spectroscopy. Both compounds improve the ablation characteristics of PMMA. For both dopants, the first step in ablation is an incubation process, in which absorption at 308 nm increases due to the production of C=C bonds along the polymer backbone. Incubation at 308 nm is similar to that observed for shorter ultraviolet wavelengths in previous studies. The principal ablation products and their corresponding temperatures are consistent with a photothermal ablation mechanism. (C) 1999 American Institute of Physics. [S0021-8979(99)04703-9].