this invention concerns a process useful for increasing the accuracy of the shape of a laser ablated feature formed on a substrate , especially where the substrate is a polymeric article . the process includes irradiating the polymeric article with laser light that has passed through a retardation plate selected from stationary adjustable plates , rotating plates or spinning plates , preferable in multiples of quarter - waves or half - waves . this invention also concerns a laser apparatus useful for making ablated features in a substrate having a radiation source ; a mask positioned between the radiation source and a substrate to be irradiated , and a retardation plate which is stationary and adjustable , rotating or spinning plates .