EXCIMER LASER ABLATION OF POLYETHYLENE TEREPHTHALATE - PREDICTION OF THRESHOLD FLUENCES FROM THERMOLYSIS RATES

Calculations of the temperature of polyethylene terephthalate (PET) illuminated with pulsed infrared (9.2-mu-m) and ultraviolet (308, 248 and 193 nm) radiation have been carried out. The results are used to estimate the extent of decomposition of PET caused by pulsed laser irradiation, on the assumption that this is caused by thermolysis. Threshold fluences for ablation of PET by CO2, XeCl, KrF and ArF lasers predicted by the treatment are in good agreement with experimental values. This supports a mechanism for excimer laser ablation of PET involving rapid relaxation of electronic energy to heat resulting in thermolysis of the polymer. These calculations do not, however, exclude the possibility of some contribution to the ablation mechanism from direct photolysis, particularly at the shorter laser wavelengths, and from multiple-photon processes.