Extreme-Ultraviolet Vortices from a Free-Electron Laser

Primož Rebernik Ribič,Luca Giannessi,Enrico Allaria,David Gauthier,Benedikt Rösner,Eléonore Roussel,Najmeh Mirian,Laura Foglia,Riccardo Mincigrucci,Alberto Simoncig,Michele Manfredda,Simone Spampinati,Nicola Mahne,Christian David,Giovanni De Ninno,Emiliano Principi,Florian Döring,Claudio Masciovecchio

doi:10.1103/physrevx.7.031036

Abstract

Extreme-ultraviolet vortices may be exploited to steer the magnetic properties of nanoparticles, increase the resolution in microscopy, and gain insight into local symmetry and chirality of a material; they might even be used to increase the bandwidth in long-distance space communications. However, in contrast to the generation of vortex beams in the infrared and visible spectral regions, production of intense, extreme-ultraviolet and x-ray optical vortices still remains a challenge. Here, we present an in-situ and an ex-situ technique for generating intense, femtosecond, coherent optical vortices at a free-electron laser in the extreme ultraviolet. The first method takes advantage of nonlinear harmonic generation in a helical undulator, producing vortex beams at the second harmonic without the need for additional optical elements, while the latter one relies on the use of a spiral zone plate to generate a focused, micron-size optical vortex with a peak intensity approaching 1014 W/cm2, paving the way to nonlinear optical experiments with vortex beams at short wavelengths.Received 20 June 2017Corrected 19 July 2018DOI:https://doi.org/10.1103/PhysRevX.7.031036Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAngular momentum of lightHigh-order harmonic generationOptical vorticesSpatial profiles of optical beamsX-ray beams & opticsAtomic, Molecular & OpticalAccelerators & Beams

Highlights

Optical vortices are helically phased light beams with a field dependence of expðilφÞ, where l is the topological charge and φ the azimuthal coordinate in the plane perpendicular to the beam propagation [1]
The first method takes advantage of nonlinear harmonic generation in a helical undulator, producing vortex beams at the second harmonic without the need for additional optical elements, while the latter one relies on the use of a spiral zone plate to generate a focused, micron-size optical vortex with a peak intensity approaching 1014 W=cm2, paving the way to nonlinear optical experiments with vortex beams at short wavelengths
The interference between the Gaussian mode produced by the first radiator section and the orbital angular momentum (OAM)-carrying light from the rest of the undulators gave a single spiral structure [28], a clear proof that the vortex beam carried a topological charge of l 1⁄4 n − 1 1⁄4 1, as shown in the right panel of Fig. 3

Summary

INTRODUCTION

Optical vortices are helically phased light beams with a field dependence of expðilφÞ, where l is the topological charge and φ the azimuthal coordinate in the plane perpendicular to the beam propagation [1]. Such beams carry an orbital angular momentum (OAM) of lħ per photon. The first scheme has the potential to produce vortex beams at high harmonics of the seed laser but has yet to be demonstrated in practice, while the latter one works only at the fundamental wavelength (i.e., the setup acts as a mode converter) and requires a coherent seed laser in the XUV or x-ray wavelength range. The setup produces a focused, micron-sized, high-intensity optical vortex without requiring extensive modifications of the FEL beamline

COHERENT OPTICAL VORTICES FROM NONLINEAR HARMONIC GENERATION

COHERENT OPTICAL VORTICES FROM A SPIRAL ZONE PLATE

DISCUSSION