Tunable orbital angular momentum in high-harmonic generation

Abstract

Optical vortices are currently one of the most intensively studied topics in optics. These light beams, which carry orbital angular momentum (OAM), have been successfully utilized in the visible and infrared in a wide variety of applications. Moving to shorter wavelengths may open up completely new research directions in the areas of optical physics and material characterization. Here, we report on the generation of extreme-ultraviolet optical vortices with femtosecond duration carrying a controllable amount of OAM. From a basic physics viewpoint, our results help to resolve key questions such as the conservation of angular momentum in highly nonlinear light–matter interactions, and the disentanglement and independent control of the intrinsic and extrinsic components of the photon's angular momentum at short-wavelengths. The methods developed here will allow testing some of the recently proposed concepts such as OAM-induced dichroism, magnetic switching in organic molecules and violation of dipolar selection rules in atoms.

Conservation of Torus-knot Angular Momentum in High-order Harmonic Generation

“…HHG is a nonperturbative phenomenon which is best understood using a semiclassical picture: an ionized electron is accelerated back to its parent ion, emitting high-frequency light in the ensuing recollision [9][10][11]. Despite the lack of a photonexchange model, HHG is often regarded as a parametric process, and its conservation properties have been explored extensively as regards energy [12], linear momentum [13], and orbital and spin angular momentum (SAM) [14][15][16][17][18][19][20][21][22][23][24][25][26].…”

Generation and Applications of Extreme-Ultraviolet Vortices

“…[19] in order to control the topological charge of the emitted harmonics by resorting to a non-collinear wave-mixing scheme with two-color laser beams. Recently, this scheme has been experimentally demonstrated [22]. In the experiment, one driving pulse at 800 nm carries zero OAM (Gaussian beam) and the other driving pulse at 400 nm carries a nonzero OAM (LG beam), generating high harmonics with controlled topological charge.…”

“…[19] by measuring the transverse phase by an interferometric technique. Very recently, different approaches that make use of specific driving laser configurations have been proposed to control and tune the OAM content of the harmonic vortices [20][21][22][23], as we will describe below. Two theoretical approaches were described in Refs.…”

Hybrid topological evolution of multi-singularity vortex beams: generalized nature for helical-Ince–Gaussian and Hermite–Laguerre–Gaussian modes

“…As distinctive structured light fields with phase singularities, optical vortices carrying orbital angular momentum (OAM) have hatched plenty of modern scientific applications in optical tweezers [1][2][3], optical communications [4,5], quantum entanglement [6][7][8] and nonlinear optics [9][10][11]. Besides the classical Laguerre-Gaussian (LG) beams carrying integer OAM with a single phase singularity, the multi-singularity vortex beams carrying fractional OAM were also reported [12][13][14][15][16][17].…”