On the generation of grooves on crystalline silicon irradiated by femtosecond laser pulses.

Irradiation of crystalline silicon with femtosecond laser pulses produces a variety of quasi-periodic surface structures, among which sub-wavelength ripples creation is largely studied. Here we report an experimental investigation and a theoretical interpretation focusing on the seldom considered issue of quasi-periodic, micron spaced grooves formation. We characterize the morphological evolution of the grooves generation and experimentally single out the variation of the threshold fluence for their formation with the number of pulses N, while typical ripples simultaneously produced in the irradiated area are always considered for comparison.

Direct Femtosecond Laser Surface Structuring with Optical Vortex Beams Generated by a q-plate.

Creation of patterns and structures on surfaces at the micro- and nano-scale is a field of growing interest. Direct femtosecond laser surface structuring with a Gaussian-like beam intensity profile has already distinguished itself as a versatile method to fabricate surface structures on metals and semiconductors. Here we present an approach for direct femtosecond laser surface structuring based on optical vortex beams with different spatial distributions of the state of polarization, which are easily generated by means of a q-plate.

Laser ablation of silicon induced by a femtosecond optical vortex beam.

We investigate laser ablation of crystalline silicon induced by a femtosecond optical vortex beam, addressing how beam properties can be obtained by analyzing the ablation crater. The morphology of the surface structures formed in the annular crater surface allows direct visualization of the beam polarization, while analysis of the crater size provides beam spot parameters. We also determine the diverse threshold fluences for the formation of various complex microstructures generated within the annular laser spot on the silicon sample.