Controlling Micron and Submicron Scale Laser Induced Surface Struc-tures on Stainless Steel with Industrial Femtosecond Lasers

Surface Texturing by USP lase

Fabrication of Biomimetic 2D Nanostructures through Irradiation of Stainless Steel Surfaces with Double Femtosecond Pulses

Femtosecond laser induced changes on the topography of stainless steel with double pulses is investigated to reveal the role of parameters such as the fluence, the energy dose and the interpulse delay on the features of the produced patterns. Our results indicate that short pulse separation (Δτ = 5 ps) favors the formation of 2D Low Spatially Frequency Laser Induced Periodic Surface Structures (LSFL) while longer interpulse delays (Δτ = 20 ps) lead to 2D High Spatially Frequency LIPSS (HSFL). The detailed investigation is complemented with an analysis of the produced surface patterns and characterization of their wetting and cell-adhesion properties. A correlation between the surface roughness and the contact angle is presented which confirms that topographies of variable roughness and complexity exhibit different wetting properties. Furthermore, our analysis indicates that patterns with different spatial characteristics demonstrate variable cell adhesion response which suggests that the methodology can be used as a strategy towards the fabrication of tailored surfaces for the development of functional implants

Highly ordered LIPSS on Au thin film for plasmonic sensing fabricated by double femtosecond pulses

We report on the single-step fabrication of homogeneous and highly ordered Laser Induced Periodic Surface Structures (LIPSS) over large areas on Au nanolayers, that can be used for plasmonic sensing. A comprehensive study on LIPSS formation on 32 nm Au film upon double, 170 fs pulse irradiation, unveiled the key importance of interpulse delay as the determining factor behind the homogeneity of laser induced structures and confirmed that highly ordered, functional LIPSS occur solely upon double pulse irradiation. In particular, the impact of pulse overlap, fluence and interpulse delay reveals that homogeneous LIPSS formation is optimized within a specific interpulse delay range. At the same time, examination of nanoscale features of the structures points out a significant differentiation of the LIPSS formation characteristics between single and double pulse irradiation. Theoretical investigation complements experimental results providing insights on the structure formation mechanism. Ellipsometric measurements validate that such structures exhibit characteristic plasmon resonances that can be exploited for sensing applications. The presented data demonstrate a novel functionality of LIPSS, while providing strong evidence of the capabilities of femtosecond double pulse irradiation as a valuable and low-cost tool for the precise fabrication of highly ordered structures

Double- and Multi-Femtosecond Pulses Produced by Birefringent Crystals for the Generation of 2D Laser-Induced Structures on a Stainless Steel Surface

Laser-induced textures have been proven to be excellent solutions for modifying wetting, friction, biocompatibility, and optical properties of solids. The possibility to generate 2D-submicron morphologies by laser processing has been demonstrated recently. Employing double-pulse irradiation, it is possible to control the induced structures and to fabricate novel and more complex 2D-textures. Nevertheless, double-pulse irradiation often implies the use of sophisticated setups for modifying the pulse polarization and temporal profile. Here, we show the generation of homogeneous 2D-LIPSS (laser-induced periodic surface structures) over large areas utilizing a simple array of birefringent crystals. Linearly and circularly polarized pulses were applied, and the optimum process window was defined for both. The results are compared to previous studies, which include a delay line, and the reproducibility between the two techniques is validated. As a result of a systematic study of the process parameters, the obtained morphology was found to depend both on the interplay between fluence and inter-pulse delay, as well as on the number of incident pulses. The obtained structures were characterized via SEM (scanning electron microscopy) and atomic force microscopy. We believe that our results represent a novel approach to surface structuring, primed for introduction in an industrial environment

On the interplay of DLIP and LIPSS upon ultra-short laser pulse irradiation

Controlling laser induced surface morphology is essential for developing specialized functional surfaces. This work presents novel, multi-scale periodic patterns with two-dimensional symmetry generated on stainless steel, polyimide and sapphire. The microstructures were realized by combining Direct Laser Interference Patterning with the generation of Laser Induced Periodic Surface Structures in a one-step process. An industrial, fiber femtosecond laser source emitting at 1030 nm with a pulse duration of 500 fs was utilized for the experiments. In the case of stainless steel, it was possible to create line-like or pillar-like surface patterns by rotating the polarization orientation with respect to the interference pattern. In the case of polyimide and sapphire, the absorption of the laser radiation was promoted by a multiphoton mechanism. In polyimide, grooves and pillars of several microns in depth were produced over an area much larger than the spot size. Finally, for sapphire, the simultaneous generation of interference-like pattern and laser induced periodic surface structures was realized. The results reported here provide valuable data on the feasibility to combine two state-of-the-art techniques with an industrial apparatus, to control the induced surface morphology