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@ARTICLE{Marotzke:624388,
      author       = {Marotzke, S. and Gupta, D. and Wang, R. -P. and Pavelka, M.
                      and Dziarzhytski, S. and Schmising, C. von Korff and Jana,
                      S. and Thielemann-Kühn, N. and Amrhein, T. and Weinelt, M.
                      and Vaskivskyi, I. and Knut, R. and Engel, D. and Braune, M.
                      and Ilchen, M. and Savio, S. and Otto, T. and Tiedtke, K.
                      and Scheppe, V. and Rönsch-Schulenberg, J. and
                      Schneidmiller, E. and Schüßler-Langeheine, C. and Dürr,
                      H. A. and Beye, M. and Brenner, G. and Pontius, N.},
      title        = {{F}irst experiments with ultrashort, circularly polarized
                      soft {X}-ray pulses at {FLASH}2},
      reportid     = {PUBDB-2025-00857, arXiv:2502.03301},
      year         = {2025},
      abstract     = {Time-resolved absorption spectroscopy as well as magnetic
                      circular dichroism with circularly polarized soft X-rays
                      (XAS and XMCD) are powerful tools to probe electronic and
                      magnetic dynamics in magnetic materials element- and
                      site-selectively. Employing these methods, groundbreaking
                      results have been obtained for instance for magnetic alloys,
                      which helped to fundamentally advance the field of ultrafast
                      magnetization dynamics. At the free electron laser facility
                      FLASH key capabilities for ultrafast XAS and XMCD
                      experiments have recently improved: In an upgrade, an
                      APPLE-III helical afterburner undulator was installed at
                      FLASH2 in September 2023. This installation allows for the
                      generation of circularly polarized soft X-ray pulses with a
                      duration of a few tens of femtoseconds covering the
                      L3,2-edges of the important 3d transition metal elements
                      with pulse energies of several uJ. Here, we present first
                      experimental results with such ultrashort X-ray pulses from
                      the FL23 beamline employing XMCD at the L-edges of the 3d
                      metals, Co, Fe and Ni. We obtain significant dichroic
                      difference signals indicating a degree of circular
                      polarization close to $100\%.$ With the pulse-length
                      preserving monochromator at beamline FL23 and an improved
                      pump laser setup, FLASH can offer important and efficient
                      experimental instrumentation for studies on ultrafast spin
                      dynamics in 3d transition metals, multilayers, and alloys.},
      keywords     = {Materials Science (cond-mat.mtrl-sci) (Other) / FOS:
                      Physical sciences (Other)},
      cin          = {FS DOOR-User / FS-FLASH / FS-FLASH-D / FS-FLASH-B},
      cid          = {$I:(DE-H253)FS_DOOR-User-20241023$ /
                      I:(DE-H253)FS-FLASH-20140814 /
                      I:(DE-H253)FS-FLASH-D-20160930 /
                      I:(DE-H253)FS-FLASH-B-20160930},
      pnm          = {631 - Matter – Dynamics, Mechanisms and Control
                      (POF4-631) / 6G2 - FLASH (DESY) (POF4-6G2) / DFG project
                      G:(GEPRIS)328545488 - TRR 227: Ultraschnelle Spindynamik
                      (328545488) / 05K22KE2 - Messplatz für ultraschnelle
                      Spindynamik bei FLASH (BMBF-05K22KE2)},
      pid          = {G:(DE-HGF)POF4-631 / G:(DE-HGF)POF4-6G2 /
                      G:(GEPRIS)328545488 / G:(DE-Ds200)BMBF-05K22KE2},
      experiment   = {EXP:(DE-H253)F-PL23-20230101},
      typ          = {PUB:(DE-HGF)25},
      eprint       = {2502.03301},
      howpublished = {arXiv:2502.03301},
      archivePrefix = {arXiv},
      SLACcitation = {$\%\%CITATION$ = $arXiv:2502.03301;\%\%$},
      doi          = {10.3204/PUBDB-2025-00857},
      url          = {https://bib-pubdb1.desy.de/record/624388},
}