Tunable orbital angular momentum in high-harmonic generation

D Gauthier,L Poletto,L F Dimauro,G Dovillaire,R Géneaux,G De Ninno,P Rebernik Ribič,T Ruchon,C Chappuis,C Spezzani,P Miotti,F Frassetto,R Cucini,G Adhikary,M Stupar,B Ressel,A Camper

doi:10.1038/ncomms14971

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.

Highlights

Optical vortices are currently one of the most intensively studied topics in optics
We report on an alternative scheme to produce optical vortices carrying an arbitrary topological charge for any harmonic order using high-harmonic generation (HHG)
This study provides an experimental verification of the conservation rule for orbital angular momentum (OAM) in HHG using two driving beams

Summary

Introduction

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. The most common light beams carrying OAM display LaguerreGaussian modes, which are solutions of the wave equation in the paraxial regime They show an azimuthal phase dependence exp( À icf) (refs 1,2), where f is the azimuthal coordinate in the transverse plane and c, called the topological charge, is indexing the mode. 12, it was theoretically demonstrated that an XUV vortex can induce charge current loops in fullerenes with an associated orbital magnetic moment, which can be controlled by tuning the topological charge of the incident beam These findings, if confirmed experimentally, could lead to new applications in magnetic switching using structured light. Subsequent experiments, demonstrated the generation of optical vortices carrying a topological charge that is a multiple of the harmonic order[17,18], in agreement with the expected conservation rule for a single driving beam[19]. These two restrictions will severely limit the applicability of the above schemes in most of the recently proposed experiments

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Conclusion