The influence of the ArF laser irradiation on the surface energy of poly(ethylene terephthalate) was investigated. An effort was also made to elucidate the physical and chemical phenomena affecting surface energy (SE). The surface chemical changes, occurring upon the irradiation, were monitored by X-ray photoelectron spectroscopy (XPS) and the changes in the surface geometrical structure were investigated by atomic force microscopy (AFM). The contact angle values obtained with test liquids of different polarity (water and diiodomethane) were measured while the surface energy was calculated by the Owens-Wendt method. The nature of the physico-chemical changes occurring in the poly(ethylene terephthalate) surface layer upon ArF laser irradiation depended mostly on the energy per unit area of the laser pulse and the number of the laser pulses. The polar and dispersive components of the surface energy increased as a result of increasing the number of the laser pulses of energy which were below that of the PET ablation threshold. (C) Koninklijke Brill NV, Leiden, 2010