DYNAMICS OF ABLATION OF POLYMETHYL METHACRYLATE FILMS BY NEAR-ULTRAVIOLET LIGHT OF AN AR+ LASER

The dynamics of cw near ultraviolet (NUV) laser ablation of polymethyl methacrylate (PMMA) films are investigated by recording the time dependence of the reflected light power. A new phenomenon in cw light ablation of PMMA, which is similar to 'incubation' pulses in excimer laser ablation, is recognized as the 'incubation' period of ablation, when polymer fragments are accumulated up to a critical density followed by a volume explosion. The incubation time is found to decrease when the light intensity in the film and/or the film temperature increases. However, for sufficiently high light intensities the incubation time depends only upon the film temperature. A dynamic model of the ablation process during the incubation time is proposed which accounts for the main features of our observations and provides a consistent quantitative description of the mechanism underlying the initial stage of ablation, i.e. before the volume explosion.