Harzic, R. leR. leHarzicDörr, D.D.DörrSauer, D.D.SauerNeumeier, M.M.NeumeierEpple, M.M.EppleZimmermann, H.H.ZimmermannStracke, F.F.Stracke2022-03-042022-03-042011https://publica.fraunhofer.de/handle/publica/22524310.1364/OL.36.000229Large-area high-spatial-frequency patterns (HSFLs) of /6 periodicity have been generated by a nanojoule-femtosecond laser scanning technique (80MHz, 170 fs, 700-950nm) at the silicon-air interface. The excellent large-area uniformity allowed reproducible and accurate measurements of the periodicity. Variation of experimental parameters as illumination geometry, and pulse energy and number showed no influence on the ripple spacing. A wavelength dependence was observed and compared to current models of HSFL formation. A particular second- armonic model was found to match the results best but needs to take into account transient changes in the refractive index under laser exposure. A second-harmonic mechanism is further supported by direct spectroscopic observation.en610535journal article