Fabrication of sub-wavelength circular diffraction gratings for high-power laser applications

In this contribution, we present the fabrication of sub-wavelength circular diffraction gratings based on Scanning Beam Interference Lithography (SBIL) method. This work was performed within a MSCA HORIZON 2020 project: “ITN GREAT” (www.itn-great-eu). Circular diffraction gratings enable the generation of laser beams with axially symmetric (azimuthal or radial) polarization states directly out of the laser cavity, which is especially interesting for laser material processing. Here, the use of axially symmetric polarization states enables an increase in cutting and drilling rates by factor ranging from 40% to 100% when compared to standard processes using linear or circular polarizations. The fabrication chain includes patterning using SBIL, where circular gratings are generated by a small interference patch that is scanned over the rotatitng substrate. This allows to pattern periodic structures with high pitch accuracy in polar coordinates directly on substrates. The structures are sub-sequently transferred into high-index material using low-pressure inductively coupled plasma (ICP) etching.