Wavelength effects in the ultraviolet-laser ablation of polycarbonate and poly(α-methylstyrene) examined by time-of-flight mass spectroscopy

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Abstract
Slow moving material (velocity ≊3×104 cm/s) ejected from polycarbonate and poly(α‐methylstyrene) targets by ultraviolet laser photoablation is probed using time‐of‐flight mass spectroscopy. The product distribution seen from polycarbonate, using resonant‐two‐photon ionization with 248‐ or 266‐nm light, consists of aromatic species smaller than the monomer. Mass spectra are similar for 355‐, 266‐, and 193‐nm ablation, and the products differ structurally from the starting material; both observations suggest that slow moving species are ejected by a thermal mechanism at all three wavelengths. 248‐nm ablation of polycarbonate near the ablation threshold, gives a different product distribution and it is argued that a cooler thermal regime is being sampled or, that photochemical effects are important. The dominant product seen in 266‐, 248‐, and 193‐nm ablation of poly(α‐methylstyrene) is the monomer in each case. Subtle differences present in the resulting mass spectra may be due to photochemical effects, but major similarities suggest that slow movers are ejected by a photothermal mechanism.