Material removal and chemical and structural changes induced by irradiation of polymer surfaces with KrF-excimer laser radiation

Holes in polypropylene (PP) and polymethylmethacrylate (PMMA) plates, 0.5 mm in thickness were drilled by irradiation with up to 3000 pulses of KrF-excimer laser radiation (λ = 248 nm) at fluences per pulse ɛ in the range 0.1–10 J/cm2, conditions which yield a laser-induced plasma/vapor plume. The process was analyzed experimentally in terms of material removal rate, optical emission of the laser-induced plasma, hole geometry, debris production at the hole edge, and chemical changes in the polymer induced by the laser irradiation. Additionally, the process was simulated using a model based on degradation of the polymer induced by optical absorption and heating, leading to gas-phase products. Such characteristics as the material removal rate as a function of fluence, the nature of the gas phase products and the deposition of debris were calculated.