Homogeneous Low Spatial Frequency LIPSS on Dielectric Materials Generated by Beam-Shaped Femtosecond Pulsed Laser Irradiation.

We report on the generation of homogenous low spatial frequency LIPSS on fused silica and sapphire with beam-shaped femtosecond pulsed laser irradiation. For the silica specimen, the periodicities of the LSFL generated by a Gaussian and a Top-Hat beam profile are compared with regard to the applied fluence, pulse overlap and angle of incidence. For both profiles, an increasing periodicity is found for an increasing pulse overlap and a decreasing periodicity for an increasing angle of incidence, in turn facilitating a fine-adjustment of the LSFL periodicity for potential applications. Furthermore, for a homogenous surface coverage with LSFL, the silica sample is rotated 40° for an angular irradiation, improving the quality of the periodic structures for Gaussian irradiation. Applying the beamshaped Top-Hat laser profile, superior LSFL with increased line width are observed. For sapphire, we focus on the generation of one-dimensional structures along straight lines with respect to different scanning directions, being either parallel or orthogonal to the laser polarization. We found an excellent quality for parallel scanning using Top-Hat beam profile as well as an increased line width as compared to Gaussian beam profile. From an applicable point of view, these high-quality structures lead to the next step texturing entire surfaces of transparent materials with homogenous microstructures for a specific adaption of the cell growth or wettability. [ABSTRACT FROM AUTHOR]