Surface functionalization (LIPSS) with Top-Hat profiles
Reference project
Laser-induced structuring with tailored focal intensity distributions
Despite the loss of intensity towards the profile edge and related inhomogeneities, Gaussian intensity distributions are preferred for structuring surfaces. In collaboration with the Otto Schott Institute for Materials Research in Jena, asphericon analyzed the effect of Top-Hat distributions with respect to their suitability for the generation of laser-induced periodic surface structures (LIPSS) on stainless steel.
Project Details
Although Gaussian intensity distributions can be used for direct surface functionalization, there are weaknesses regarding the quality. The intensity decreases at the edges of the beam and thus causes inhomogeneity. An adaptation of the focal intensity distribution offers great potential. The beam shaping component a|AiryShape ensures that several intensity distributions can be generated in different working planes with one set-up. In cooperation with Otto Schott Institute of Materials Research (OSIM) in Jena, asphericon analyzed various tailored intensity distributions (e.g. Top-Hat, Donut) with respect to their suitability for the generation of laser-induced periodic surface structures (LIPSS = laser-induced periodic surface structures) on stainless steel.
Project Realization
LIPSS are created by interference effects in the spot of the focused laser beam on the material surface. They are much smaller than those realized by direct material ablation and act as a grating while their period is close to the initial laser wavelength. Figure a shows an LIPSS pattern produced by unidirectional scanning of the surface between two adjacent scan lines and the Gaussian beam profile in the beam waist. The corresponding focal spot diameter (2wf = 34 μm) is indicated by the circle in the scanning electron micrograph (SEM).
Figure: Scanning electron micrographs of stainless steel surfaces structured with LIPSS; white circles indicate focal spot beam diameters, white arrows indicate direction; insets show cross-sections of beam profiles
It becomes evident that the generated grating like structures consist of highly regular LIPSS oriented perpendicular to the linear polarization. The micrograph reveals that LIPSS can be coherently written over a large area despite the line wise scanning process. The properties of the grating with respect to the spatial period, orientation, and homogeneity can be quantitatively described by 2D-FT of the SEM micrograph. The Top-Hat profiles (Fig. b and c) were generated with the a|AiryShape. The SEM micrograph in Fig. c demonstrates that the scanning velocity can be doubled without further optimization of the processing parameters. The calculated Fourier transformation shows that the quality of the surface pattern remained almost constant, while reducing the processing time by a factor of 2 (approx. 30 s per cm2), resulting in a significant advantage for the economic scaling of the structuring process to large surface areas.
Optics for surface functionalization (LIPSS) at a glance:
- Compact beam shaper for generating a focused Top-Hat beam
- Doubling the scanning velocity
- Reduction of the processing time by a factor of 2 with constant quality of surface pattern
Learn more about the principle of our beam shaper a|AiryShape at: asphericon.com/en/solutions/products/beamtuning/beam-shaping/
