1-D and 2-D surface structuring of steel by bursts of femtosecond laser pulses

We obtained 1-D and 2-D periodic surface structures and investigated the influence of number of sub-pulses and polarization on their morphology. In particular, when bursts composed by all-aligned linearly polarized sub-pulses were used, 1-D LIPSS were obtained with different periodicity and depths depending on the number of sub-pulses. Bursts with crossed linear polarization or circular polarization sub-pulses produced 2-D LIPSS with morphology varying from triangular structures arranged in hexagonal lattice to pillar-like ordered or disordered structures depending on the bursts features.

In this work, we report on the fabrication of laser induced periodic surface structures (LIPSS) on stainless steel, using bursts of 200 fs sub-pulses at a wavelength of 1030 nm. A cascade of birefringent crystals was used to generate the bursts with tunable number of sub-pulses and intra-burst delays varying between 1.5 ps and 24 ps. Being such a delay shorter than the typical electron-lattice relaxation time in metals, the sub-pulses impinge on the sample surface when the material is still in a transient state after excitation from the first sub-pulse, thus allowing peculiar structures to be generated depending on the burst features.