title: Extreme Ultraviolet Fractional Orbital Angular Momentum Beams from High Harmonic Generation.
abstract: We investigate theoretically the generation of extreme-ultraviolet (EUV) beams carrying fractional orbital angular momentum. To this end, we drive high-order harmonic generation with infrared conical refraction (CR) beams. We show that the high-order harmonic beams emitted in the EUV/soft x-ray regime preserve the characteristic signatures of the driving beam, namely ringlike transverse intensity profile and CR-like polarization distribution. As a result, through orbital and spin angular momentum conservation, harmonic beams are emitted with fractional orbital angular momentum, and they can be synthesized into structured attosecond helical beams -or "structured attosecond light springs"- with rotating linear polarization along the azimuth. Our proposal overcomes the state of the art limitations for the generation of light beams far from the visible domain carrying non-integer orbital angular momentum and could be applied in fields such as diffraction imaging, EUV lithography, particle trapping, and super-resolution imaging.
authors.affiliation: Departament de Física, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Spain.|Center of Advanced European Studies and Research, 53175 Bonn, Germany.
authors.forename: Alex
authors.initials: A
authors.lastname: Turpin
authors.affiliation: Grupo de Investigación en Aplicaciones del Láser y Fotónica, Departamento de Física Aplicada, University of Salamanca, E-37008, Salamanca, Spain.
authors.forename: Laura
authors.initials: L
authors.lastname: Rego
authors.affiliation: Grupo de Investigación en Aplicaciones del Láser y Fotónica, Departamento de Física Aplicada, University of Salamanca, E-37008, Salamanca, Spain.
authors.forename: Antonio
authors.initials: A
authors.lastname: Picón
authors.affiliation: Grupo de Investigación en Aplicaciones del Láser y Fotónica, Departamento de Física Aplicada, University of Salamanca, E-37008, Salamanca, Spain.
authors.forename: Julio
authors.initials: J
authors.lastname: San Román
authors.affiliation: Grupo de Investigación en Aplicaciones del Láser y Fotónica, Departamento de Física Aplicada, University of Salamanca, E-37008, Salamanca, Spain.
authors.forename: Carlos
authors.initials: C
authors.lastname: Hernández-García