Mechanism for self-formation of periodic structures on a plastic polymer surface using a nanosecond and femtosecond laser pulses

Abstract

The high UV laser dose at 193 nm induces grooves on poly allyl diglycol carbonate PADC (CR39) at normal irradiation. The spatial period exhibits to be nearly invariant for azimuth and polar angles indicating a loose dependence on the incident angles but the LIPSS (Laser-induced periodic surface structures) are always parallel to the P polarization component of the incident beam. The most common approach to explain LIPSS formation is related to the Sipe theory which does not account for all the observed phenomena especially LIPSS with periodicity larger than the laser wavelength. In fact the LIPSS is a multi parameter mechanism based on surface rippling, acoustic modulation and laser ablation and etc. In experiment with CR-39 polymer, laser irradiation produce a very tiny melting layer of mixture of monomer due to depolymerization on the surface and it seems capillary wave is responsible for grooves formation.