Bright circularly polarized soft X-ray high harmonics for X-ray magnetic circular dichroism
2015 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 112, no 46, 14206-14211 p.Article in journal (Refereed) PublishedText
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.
Place, publisher, year, edition, pages
2015. Vol. 112, no 46, 14206-14211 p.
X-rays, high harmonics generation, magnetic material, ultrafast light science, phase matching
IdentifiersURN: urn:nbn:se:uu:diva-271024DOI: 10.1073/pnas.1519666112ISI: 000365170400046PubMedID: 26534992OAI: oai:DiVA.org:uu-271024DiVA: diva2:891124
FunderEU, FP7, Seventh Framework Programme, 328334German Research Foundation (DFG), GR 4234/1-1Swedish Research CouncilEU, FP7, Seventh Framework Programme, 281043