Ablation of pristine and radiation exposed CR-39 polymer using a 157nm laser

In this paper, an investigation of the ablation of polymer CR-39 (allyl diglycol carbonate) surface using 157 nm F₂ laser radiation was described, motivated by an interest in producing optical microstructures and the possibility of revealing radiation damage tracks by photoablation. The effective absorption coefficient and the etch depth-fluence were plotted. Canonical structure developed was compared to that of other UV laser-polymer ablation experiments. Results were confirmed by modelling which provides good description of the fringes and scalloping effect. Experiments using nano- and micro-particles to seed cones, and micro- whiskers to generate analogous prismatic structures on CR-39 are currently underway. CR-39 samples were also exposed to alpha particles (4.87 and 4.61 MeV) which showed no morphological evidence of radiation damage when etched using F₂ laser. This is likely because the radius of damage tracks in the polymer is typically ~5 nm and hence ´un-resolvable´ at a wavelength of 157 nm. However, interesting effects have been seen in radiation-exposed samples that were chemically etched in NaOH to reveal deep tracks of a few microns diameter and then ablated at 157 nm. These include smoothing of the edges of tracks due to melt flow relaxation and, under multiple pulse exposure, a significantly increased density of conical structures, apparently seeded by the edges of tracks.