Extreme-ultraviolet spatiotemporal vortices via high harmonic generation

TL;DR

This paper demonstrates the generation of extreme-ultraviolet spatiotemporal vortices with transverse orbital angular momentum using high harmonic generation driven by near-infrared STOV pulses, combining theoretical and experimental approaches.

Contribution

It introduces the first experimental and theoretical demonstration of EUV spatiotemporal vortices generated via high harmonic generation from near-infrared STOV pulses.

Findings

EUV STOVs exhibit conjugated spatiotemporal and spatiospectral vortex pairs.

Theoretical models match experimental results of EUV vortex generation.

Generated EUV vortices carry high topological charge and transverse OAM.

Abstract

Spatiotemporal optical vortices (STOV) are space-time structured light pulses with a unique topology that couples spatial and temporal domains and carry transverse orbital angular momentum (OAM). Up to now, their generation has been limited to the visible and infrared regions of the spectrum. During the last decade, it was shown that through the process of high-order harmonic generation (HHG) it is possible to up-convert spatial optical vortices that carry longitudinal OAM from the near-infrared into the extreme-ultraviolet (EUV), thereby producing vortices with distinct femtosecond and attosecond structure. In this work we demonstrate theoretically and experimentally the generation of EUV spatiotemporal and spatiospectral vortices using near infrared STOV driving laser pulses. We use analytical expressions for focused STOVs to perform macroscopic calculations of HHG that are directly compared to the experimental results. As STOV beams are not eigenmodes of propagation, we characterize the highly-charged EUV STOVs both in the near and far fields, to show that they represent conjugated spatiotemporal and spatiospectral vortex pairs. Our work provides high-frequency light beams topologically coupled at the nanometer/attosecond scales domains with transverse OAM, that could be suitable to explore electronic dynamics in magnetic materials, chiral media, and nanostructures.