Ultraviolet-laser-induced periodic surface structures

We report the first systematic investigation into the properties of ultraviolet-laser-induced periodic surface structures that can be produced on nominally smooth surfaces. The study investigates the dependence of the patterns that are produced on Ge and Al by a KrF 249-nm laser on incident fluence and both the polarization and angle of incidence of the light. At high fluence we show that the results are consistent with the assumption that the surface melts uniformly, whereas the patterns formed at low fluence can be explained on the basis of the localized melting of the surface. For P-polarized light we find two dominant patterns, one perpendicular to the polarization and one parallel to it. For S-polarized light we report the first observation of two new patterns, one parallel and one perpendicular to the polarization, of which the latter is explained by invoking a new formation mechanism. The results show that for P-polarized light at large angles of incidence the ripple spacing shows large deviations from its previously expected value. The results are shown to be in excellent agreement with a previously developed first-principles theory. In addition, we report surface structures that are consistent with the idea of capillary waves being launched and subsequently frozen on the surface of the material.