Laser-induced periodic structures created in a surface after irradiating with pulses of an energy of (fundamental of Ti:sapphire laser, pulse duration of 150 fs, central wavelength of 800 nm, ), and (a) laser irradiated region. (b) Spatial frequency spectrum determined by the 2D-FT (image postprocessed by nonlinear filtering, field of view corresponding to a field of interest of in the center of the irradiated zone). (c) Outer region of (a). (d) Central region of (a). The double arrow indicates the orientation of the polarization vector.
Behavior at small numbers of pulses: laser-induced random (meandering) structures created in a surface after irradiating with pulses (fundamental of Ti:sapphire laser, pulse duration of 150 fs, central wavelength of 800 nm) at a pulse energy of . (a) SEM image. (b) Corresponding 2D-FT data (image postprocessed by nonlinear filtering, field of interest ). The double arrow indicates the orientation of the polarization vector.
Square of the diameter of the ablated region in dependence on the natural logarithmic value of the pulse energy for two different numbers of pulses: (a) and (b) . A damage accumulation effect is indicated by a shift of the threshold energy toward lower values at higher numbers of pulses.
SEM characterization of laser-induced nanostructures obtained over extended regions by a controlled translation of the sample. Two cases were studied: sample movement perpendicular to polarization [case I in (a)–(c); pulse energy of , sample speed of 1 mm/s] and parallel to the polarization [case II in (d)–(f), pulse energy of , sample speed of 0.5 mm/s]. The appearance of the HFSL structures can clearly be recognized at higher resolution [(b) and (e)]. Grayscale maps in (b) and (e) were processed by 2D-FT [(c) and (f)]. 2D-FT spectra (calculated for selected areas of ) indicate the enhancement of periodicity by two distinct maxima.
AFM image of the HSFL generated in the extended region [pulse and pulse repetition rate of 966 Hz].
Short-wavelength generation of HSFL: quasiperiodic nanostructures induced in a surface by the second harmonic wave of the Ti:sapphire laser (wavelength around 400 nm). Here, the number of pulses was and the pulse energy was about . The double arrow indicates the orientation of polarization vector.
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