Bright circularly polarized soft X-ray high harmonics for X-ray magnetic circular dichroism

Tingting Fan, Patrik Grychtol, Ronny Knut, Carlos Hernández-García, Daniel D. Hickstein, Dmitriy Zusin, Christian Gentry, Franklin J. Dollar, Christopher A. Mancuso, Craig W. Hogle, Ofer Kfir, Dominik Legut, Karel Carva, Jennifer L. Ellis, Kevin M. Dorney, Cong Chen, Oleg G. Shpyrko, Eric E. Fullerton, Oren Cohen, Peter M. OppeneerDejan B. Miloševic, Andreas Becker, Agnieszka A. Jaron-Becker, Tenio Popmintchev, Margaret M. Murnane*, Henry C. Kapteyn

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

220 Scopus citations

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 exceeding160 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 phasematching 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.

Original languageEnglish
Pages (from-to)14206-14211
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume112
Issue number46
DOIs
StatePublished - 17 Nov 2015
Externally publishedYes

Keywords

  • High harmonics generation
  • Magnetic material
  • Phase matching
  • Ultrafast light science
  • X-rays

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