title: Bright circularly polarized soft X-ray high harmonics for X-ray magnetic circular dichroism.
abstract: We demonstrate, to our knowledge, the first bright circularly polarized high-harmonic beams in the soft X-ray region of the electromagnetic spectrum, and use them to implement X-ray magnetic circular dichroism measurements in a tabletop-scale setup. Using counterrotating circularly polarized laser fields at 1.3 and 0.79 µm, we generate circularly polarized harmonics with photon energies exceeding 160 eV. The harmonic spectra emerge as a sequence of closely spaced pairs of left and right circularly polarized peaks, with energies determined by conservation of energy and spin angular momentum. We explain the single-atom and macroscopic physics by identifying the dominant electron quantum trajectories and optimal phase-matching conditions. The first advanced phase-matched propagation simulations for circularly polarized harmonics reveal the influence of the finite phase-matching temporal window on the spectrum, as well as the unique polarization-shaped attosecond pulse train. Finally, we use, to our knowledge, the first tabletop X-ray magnetic circular dichroism measurements at the N4,5 absorption edges of Gd to validate the high degree of circularity, brightness, and stability of this light source. These results demonstrate the feasibility of manipulating the polarization, spectrum, and temporal shape of high harmonics in the soft X-ray region by manipulating the driving laser waveform.
authors.affiliation: Department of Physics and JILA, University of Colorado, Boulder, CO 80309-0440; murnane@jila.colorado.edu tingting.fan@colorado.edu.
authors.forename: Tingting
authors.initials: T
authors.lastname: Fan
authors.affiliation: Department of Physics and JILA, University of Colorado, Boulder, CO 80309-0440;
authors.forename: Patrik
authors.initials: P
authors.lastname: Grychtol
authors.affiliation: Department of Physics and JILA, University of Colorado, Boulder, CO 80309-0440;
authors.forename: Ronny
authors.initials: R
authors.lastname: Knut
authors.affiliation: Department of Physics and JILA, University of Colorado, Boulder, CO 80309-0440; Grupo de Investigación en Óptica Extrema, Universidad de Salamanca, Salamanca 37008, Spain;
authors.forename: Carlos
authors.initials: C
authors.lastname: Hernández-García
authors.affiliation: Department of Physics and JILA, University of Colorado, Boulder, CO 80309-0440;
authors.forename: Daniel D
authors.initials: DD
authors.lastname: Hickstein
authors.affiliation: Department of Physics and JILA, University of Colorado, Boulder, CO 80309-0440;
authors.forename: Dmitriy
authors.initials: D
authors.lastname: Zusin
authors.affiliation: Department of Physics and JILA, University of Colorado, Boulder, CO 80309-0440;
authors.forename: Christian
authors.initials: C
authors.lastname: Gentry
authors.affiliation: Department of Physics and JILA, University of Colorado, Boulder, CO 80309-0440;
authors.forename: Franklin J
authors.identifier: http://orcid.org/0000-0003-3346-5763
authors.initials: FJ
authors.lastname: Dollar
authors.affiliation: Department of Physics and JILA, University of Colorado, Boulder, CO 80309-0440;
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Mancuso
authors.affiliation: Department of Physics and JILA, University of Colorado, Boulder, CO 80309-0440;
authors.forename: Craig W
authors.initials: CW
authors.lastname: Hogle
authors.affiliation: Solid State Institute and Physics Department, Technion, Haifa 32000, Israel;
authors.forename: Ofer
authors.initials: O
authors.lastname: Kfir
authors.affiliation: IT4Innovations Center, VSB Technical University of Ostrava, CZ 708 33 Ostrava, Czech Republic; Faculty of Mathematics and Physics, Department of Condensed Matter Physics, Charles University in Prague, CZ-12116 Prague 2, Czech Republic;
authors.forename: Dominik
authors.initials: D
authors.lastname: Legut
authors.affiliation: Faculty of Mathematics and Physics, Department of Condensed Matter Physics, Charles University in Prague, CZ-12116 Prague 2, Czech Republic; Department of Physics and Astronomy, Uppsala University, 75120 Uppsala, Sweden;
authors.forename: Karel
authors.initials: K
authors.lastname: Carva
authors.affiliation: Department of Physics and JILA, University of Colorado, Boulder, CO 80309-0440;
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Ellis
authors.affiliation: Department of Physics and JILA, University of Colorado, Boulder, CO 80309-0440;
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Dorney
authors.affiliation: Department of Physics and JILA, University of Colorado, Boulder, CO 80309-0440;
authors.forename: Cong
authors.initials: C
authors.lastname: Chen
authors.affiliation: Department of Physics, University of California San Diego, La Jolla, CA 92093;
authors.forename: Oleg G
authors.initials: OG
authors.lastname: Shpyrko
authors.affiliation: Center for Magnetic Recording Research, University of California San Diego, La Jolla, CA 92093-0401;
authors.forename: Eric E
authors.initials: EE
authors.lastname: Fullerton
authors.affiliation: Solid State Institute and Physics Department, Technion, Haifa 32000, Israel;
authors.forename: Oren
authors.initials: O
authors.lastname: Cohen
authors.affiliation: Department of Physics and Astronomy, Uppsala University, 75120 Uppsala, Sweden;
authors.forename: Peter M
authors.initials: PM
authors.lastname: Oppeneer
authors.affiliation: Faculty of Science, University of Sarajevo, 71000 Sarajevo, Bosnia and Herzegovina; Academy of Sciences and Arts of Bosnia and Herzegovina, 71000 Sarajevo, Bosnia and Herzegovina; Max-Born-Institut, 12489 Berlin, Germany.
authors.forename: Dejan B
authors.initials: DB
authors.lastname: Milošević
authors.affiliation: Department of Physics and JILA, University of Colorado, Boulder, CO 80309-0440;
authors.forename: Andreas
authors.initials: A
authors.lastname: Becker
authors.affiliation: Department of Physics and JILA, University of Colorado, Boulder, CO 80309-0440;
authors.forename: Agnieszka A
authors.initials: AA
authors.lastname: Jaroń-Becker
authors.affiliation: Department of Physics and JILA, University of Colorado, Boulder, CO 80309-0440;
authors.forename: Tenio
authors.initials: T
authors.lastname: Popmintchev
authors.affiliation: Department of Physics and JILA, University of Colorado, Boulder, CO 80309-0440; murnane@jila.colorado.edu tingting.fan@colorado.edu.
authors.forename: Margaret M
authors.initials: MM
authors.lastname: Murnane
authors.affiliation: Department of Physics and JILA, University of Colorado, Boulder, CO 80309-0440;
authors.forename: Henry C
authors.initials: HC
authors.lastname: Kapteyn
keywords: X-rays; high harmonics generation; magnetic material; phase matching; ultrafast light science