Highly efficient harmonic vortex generation from a laser irradiated hollow-cone target

It has been recently reported that ultraviolet harmonic vor-tices can be produced when a high-power circular-polarized laser pulse travels through a micro-scale waveguide. How-ever, the harmonic generation quenches typically after a few tens of microns of propagation, due to the buildup of electrostatic potential that suppresses the amplitude of the surface wave. Here we propose to use a hollow-cone channel to overcome this obstacle. When traveling in a cone target, the laser intensity at the entrance is relatively low to avoid extracting too many electrons, while the slow focusing by the cone channel subsequently counters the established elec-trostatic potential, allowing the surface wave to maintain a high amplitude for a much longer distance. According to three-dimensional particle-in-cell simulations, the harmonic vortices can be produced with very high efficiency >20%. The proposed scheme paves the way for the development of powerful optical vortices sources in the extreme ultravio-let regime-an area of significant fundamental and applied physics potential. (c) 2023 Optica Publishing Group