PICOSECOND AND SUBPICOSECOND VISIBLE LASER-ABLATION OF OPTICALLY TRANSPARENT POLYMERS

The ablation rates, as a function of the laser fluence, of the optical ly transparent polymers, Nylon-6,6 and PMMA, are reported using picose cond and subpicosecond laser pulses, obtained from a Regenerative Ampl ified Nd:YAG laser system. The laser pulses had a duration of 100 ps a t 1064 and 532 nm wavelengths and 0.8 ps at 595 nm. The ablation rate results indicate a strong saturation behaviour for both polymers in th e investigated irradiation conditions. The material removal is 2-3 tim es higher in the case of the visible (532 nm) picosecond laser ablatio n experiments. The surface topology of the polymers was also studied. The obtained Atomic Force Microscopy images reveal no mechanical damag e in the inner ablation crater wall. The qualitative analysis of the a blation mechanism for ultrashort pulse laser irradiation reveals a com bination of photochemically induced direct bond dissociation and a pho tothermal process due to the relaxation of the excited polymers within the vibrational levels of the ground state. (C) 1998 Elsevier Science B.V. All rights reserved.