We introduce a novel sub-diffraction direct laser writing process and discuss its advantages compared to common lithographic methods. The fundamental idea is based on the combination of a Stimulated Emission Depletion (STED) with the effect of an Excited State Absorption (ESA). Analogous to the STED-microscopy, an excited spatial volume below the diffraction limit is created. The modified optical properties of this volume compared to the non-excited surrounding regions are used for the subsequent spatially restricted processing based on an ESA. In combination with a required STED- and ESA-compatibility, a variety of potentially suitable processes for excitation, stimulated emission, and ESA are presented for various materials. Here, direct semiconductors such as ZnO are of particular interest for a STED-process. The second essential requirement, an ESA-based processing, was demonstrated experimentally for the first time at a 200 nm thinn ZnO-layer sputtered on a fused silica substrate. For this purpose, an experimental setup consisting of two ns-lasers, one for excitation and one for the ESA-based processing, as well as a variable time delay, was used.
The formation of laser-induced periodic surface structures (LIPSS) was investigated on different types of materials such as metals, glasses and composites. For this purpose, the broad spectrum of processing parameters (e.g., laser wavelength, beam polarization, peak fluence and pulse number) was used to precisely adjust the properties of the resulting ripple pattern. The formation process and potential applications were discussed, among other things, using the example of mechano-responsive changes in structural colors, heterogeneous wetting of substrate surfaces, and the tribological properties of composite materials selectively structured with LIPSS. Our studies provide qualitative insights into the LIPSS formation process and present potential applications of the structured surfaces in the fields of sensors, microfluidic devices, and implant materials.
Gaussian intensity profiles are widely used in the field of laser material processing. Nevertheless, there are applications, where the inhomogeneous beam profile is not acceptable. We show that refractive beam shaping systems provide very good results for generating tailored focal intensity distributions, e.g. top-hat or doughnut shaped profiles. Even though using just one beam shaping system the width of the profiles is scalable. The device is suitable for working with a scanner and F-Theta lens as commonly used for material processing. Results of material processing of steel are compared for different focal intensity distributions.
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