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

TL;DR

This paper proposes a hollow-cone target design that significantly enhances the efficiency of ultraviolet harmonic vortex generation by maintaining high surface wave amplitude over longer distances, reaching over 20% efficiency.

Contribution

Introducing a hollow-cone channel to sustain surface wave amplitude and boost harmonic vortex generation efficiency in laser-plasma interactions.

Findings

Efficiency boosted by nearly an order of magnitude (>20%)

Hollow-cone targets mitigate pre-heating effects

Longer propagation of surface waves in cone targets

Abstract

It has been recently reported that ultraviolet harmonic vortices can be produced when a high-power circular-polarized laser pulse travels through a micro-scale waveguide. However, the harmonic generation quenches typically after a few tens of microns of propagation, due to the build-up of electrostatic potential that suppresses the amplitude of the surface wave. Here we propose to utilize a hollow-cone channel to overcome this obstacle. When traveling in a cone target, the laser intensity gradually increases, allowing the surface wave to maintain a high amplitude for a much longer distance. The harmonic vortices can be produced with very high efficiency. According to three-dimensional particle-in-cell simulations, the overall efficiency are boosted by almost one order of magnitude, reaching $>20\%$. It is also found that using the cone targets can mitigate efficiency decline due to pre-heating of plasma by laser prepulse. The proposed scheme paves the way to the development of powerful optical vortices sources in the extreme ultraviolet regime - an area of significant fundamental and applied physics potential.