Multiple pulse laser ablation of biaxially stretched poly(ethylene therephthalate) (PET) was performed in air with a standard ArF excimer laser (193 nm) to produce micro channels. "Scanning ablation", with the sample moving during irradiation, was extensively studied. A new type of surface structure on the channel floor was obtained. The channel floor originates from irradiation of the ramp at the end of the channel. Three structure types were observed on ablated ramps. Each of these structures occurs within a certain range of ramp angles. The angle of incident light is not responsible for the structural changes, which is in a,agreement with the literature. Other possible mechanisms, such as the influence of the sample geometry near the irradiated area influencing the structure formed on the ablated surface, are discussed.