High-Harmonic Generation and Spin-Orbit Interaction of Light in a Relativistic Oscillating Window

Abstract

When a high power laser irradiates a small aperture on a solid foil target, the strong laser field drives surface plasma oscillation at the rim of the aperture, which acts as a "relativistic oscillating window". The diffracted light travels though such an aperture contains high-harmonics of the fundamental laser frequency. When the driving laser is circularly polarised, the high-harmonic generation (HHG) process facilitates a conversion of the spin angular momentum of the fundamental light into the intrinsic orbital angular momentum of the harmonics. By means of theoretical modelling and fully 3D particle-in-cell simulations, it is shown the harmonic beams of order n are optical vortices with topological charge |l| = n − 1. When the driving laser is significantly intense, the HHG is dramatically enhanced through a surface wave breaking effect, which leads to a universal power-law spectrum In ∝ n −3.5 at ultra-relativistic limit, where In is the intensity of the nth harmonic. This work opens up a new realm of possibilities for producing intense extreme ultraviolet vortices, and diffraction-based HHG studies at relativistic intensities.

Intense high-harmonic optical vortices generated from a micro-plasma-waveguide irradiated by a circularly polarized laser pulse

“…The spectra can be fitted with a powerlaw shape I n ∝ n −3.5 , where I n is the intensity of the nth harmonics. This indicates the HHG mechanism is very similar to that of ROW [26]. This is expected because a waveguide can be considered as a train of co-axial diffraction apertures with the same radii.…”

“…Recently, we demonstrated [26] that high-harmonic optical vortices can also be generated when a high-power CP laser diffracts through a relativistic oscillating window (ROW). The laser drives chiral relativistic electron oscillations at the periphery of an aperture, which produces high-order harmonics via Doppler effect and facilitates spin-orbital interaction of light.…”

“…Since the high-order harmonic vortices are generated through a similar mechanism with the ROW [26], namely the chiral electron oscillation on the periphery of a highpower laser beam, the HHG efficiency depends crucially on the amplitude of the oscillation. A large amplitude is associated with the surface wave breaking (SWB) effect, i.e.…”

Intense harmonic generation driven by a relativistic spatiotemporal vortex beam

“…Concurrent with the progress in high-power lasers [6,7] , the production of intense spatial vortex beams in the relativistic region (> 10 18 W cm −2 for a laser wavelength of ∼ 1 µm) has been theoretically proposed [8][9][10] and demonstrated in laboratories [11][12][13] . Such advanced light sources provide new possibilities for light-matter interactions, such as donut/twist wakefield acceleration [14][15][16] , attosecond electron bunch generation [17][18][19] , formation of a large magnetic field [20] , high harmonics generation (HHG) [12,21,22] , and the spin-orbital interaction [23][24][25][26][27] . In particular, the SAM and/or OAM of fundamental-frequency photons are transferred into high harmonics during HHG.…”

Deciphering in situ electron dynamics of ultrarelativistic plasma via polarization pattern of emitted gamma photons

“…Concluding, we demonstrate that the polarization properties of γ-photons emitted from the energetic plasma driven by a circularly polarized laser pulse provide extra degrees of freedom of information on the transient electron acceleration dynamics, self-generated magnetic fields, plasma QED status, and on the regimes of laser-plasma interaction. This information will help in better understanding of the underlying mechanisms of observed phenomena in broad high-intensity interaction scenarios including ion acceleration [48][49][50][51], elec-tron direct acceleration [39], high-harmonic generation [52,53], brilliant photon emission [54], ultradense nanopinches [55], and e − e + pair plasma cascades [56]. For astrophysics aspects, our results indicate that the γ-photon LP orientation modulated by the particle acceleration gradient is potentially connected to the correlation between the observed GPP and universe magnetic fields [9].…”