Diffraction-driven laser surface nanostructuring: Towards patterning with curved periodic surface structures

The quest for miniaturization of devices and control over surface properties motivate rigorous efforts to artificially fabricate surfaces with nanometer features. Here we present a method for fabricating curved, meandering grooves with submicrometer spacing by laser irradiation in liquid. We show that this is possible by using the cavitation bubbles formed during irradiation as diffraction objects to spatially modulate the intensity distribution of the beam, which is imprinted into the top layer of material surface. The bubbles are manipulated with thermo-optical tweezers by thermocapillary forces generated by the temperature gradient in the liquid around the irradiation spot. The presented results show that high viscosity of the liquid, producing laminar flow conditions, provides sufficient stability of the cavitation bubble dynamics for the generation of regular arc-shaped concentric microgroove channels with a depth of several hundred nanometers and a radius of curvature in the micrometer range. Their position is determined by the beam guiding pattern. The results clearly show that cavitation bubbles can be used as an aid in laser ablation in liquids and not just as an undesirable effect, as usually classified in the literature.