Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 112, Issue 46, Pages 14206-14211Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1519666112
Keywords
X-rays; high harmonics generation; magnetic material; ultrafast light science; phase matching
Categories
Funding
- Department of Energy (DOE) Office of Basic Energy Sciences X-Ray Scattering Program
- National Science Foundation (NSF) Physics Frontier Center Program [PHY-1125844]
- NSF [DGE-1144083]
- European Union (EU) Seventh Framework Program for Research and Technological Development, under REA Grant [328334]
- Junta de Castilla y Leon [SA116U13, UIC016]
- MINECO [FIS2013-44174-P]
- US NSF [PHY-1125844, PHY-1068706, CNS-0821794]
- Deutsche Forschungsgemeinschaft [GR 4234/1-1]
- Swedish Research Council
- EU Seventh Framework Programme Grant, FemtoSpin [281043]
- Czech Science Foundation [15-08740Y]
- IT4Innovations Centre of Excellence Project - European Regional Development Fund [CZ.1.05/1.1.00/02.0070]
- national budget of the Czech Republic Project Large Research, Development and Innovations Infrastructures [LM2011033]
- US DOE, Office of Science, Office of Basic Energy Sciences [DE-SC0001805]
- US DOE Office of Basic Energy Sciences [DE-SC0003678]
- Division Of Physics
- Direct For Mathematical & Physical Scien [1125844] Funding Source: National Science Foundation
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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 mu m, 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 N-4,N-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.
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