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

Poly(methyl methacrylate) (PMMA) is highly resistant to laser ablation at 3 08 nm. Either very high fluences or absorbing dopants must be used to ablat e PMMA efficiently at this wavelength. We investigate two dopants, pyrene a nd a common solvent, chlorobenzene, using time-of-flight mass spectroscopy. Both compounds improve the ablation characteristics of PMMA. For both dopa nts, the first step in ablation is an incubation process, in which absorpti on 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 ult raviolet wavelengths in previous studies. The principal ablation products a nd their corresponding temperatures are consistent with a photothermal abla tion mechanism. (C) 1999 American Institute of Physics. [S0021-8979(99)0470 3-9].