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Large-area, uniform, high-spatial-frequency ripples generated on silicon using a nanojoule-femtosecond laser at high repetition rate

: Harzic, R. le; Dörr, D.; Sauer, D.; Neumeier, M.; Epple, M.; Zimmermann, H.; Stracke, F.


Optics Letters 36 (2011), No.2, pp.229-231
ISSN: 0146-9592
Journal Article
Fraunhofer IBMT ()

Large-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.