157 nm F₂ laser ablation of polyethylene terephthalate

The ablation of polyethylene terephthalate (PET) by pulsed 157 nm radiation from a fluorine laser has been studied. Etch depth measurements give an effective absorption coefficient (k_e) of (1.1_-0.4^+0.5)*10⁵ cm^-1 corresponding to a threshold fluence for ablation (F_T) of (29+or-6) mJ cm^-2. The gaseous products of the ablation are CO, CO₂, CH₄, C₂H₂, C₂H₄, C₄H₂, C₄H₄, benzene and CH₃CHO, similar to those found in the XeCl laser and the ArF laser ablation. The ablation threshold is lower than a value predicted on the basis of thermal decomposition alone, suggesting that there is a significant photochemical contribution to the ablation mechanism.