Relativistic high-order harmonic generation of spatiotemporal optical vortices

It is well known that light can possess spin angular momentum (SAM) and orbital angular momentum (OAM) in the longitudinal direction. Interesting novel light with transverse SAM or OAM has also been discovered recently, with the latter being called spatiotemporal optical vortices. Here we present a route to generate spatiotemporal optical vortices by means of high harmonic generation from relativistic laser plasma interactions. Three-dimensional particle-in-cell simulations show the evidence of edge dislocations in wave front structures and circulating energy flow in space-time. Further calculations of the SAM, OAM and total angular momentum confirm the harmonics carrying pure transverse OAM with noninteger values. The results open up a possibility to generate intense spatiotemporal optical vortices in the extreme ultraviolet region with attosecond duration.