Nanosecond and femtosecond UV laser ablation of polymers: Influence of molecular weight

We examine the nanosecond and femtosecond UV laser ablation of poly(methyl methacrylate) (PMMA) as a function of molecular weight (Mw). For laser ablation with nanosecond laser pulses, at the excimer wavelengths 248 nm and 193 nm, we show that high temperatures develop; yet the dynamics of material ejection differs depending on polymer Mw. The results on the nanosecond ablation of polymers are accounted within the framework of bulk photothermal model and the results of molecular dynamics simulations. Turning next to the 248 nm ablation with 500 fs laser pulses, the ablation threshold and etching rates are also found to be dependent on polymer Mw. In addition, ablation results in morphological changes of the remaining substrate. Plausible mechanisms are advanced.