Gregor Hartmann

Circular dichroism measurements at an x-ray free-electron laser with polarization control

A non-destructive diagnostic method for the characterization of circularly polarized, ultraintense, short wavelength free-electron laser (FEL) light is presented. The recently installed Delta undulator at the LCLS (Linac Coherent Light Source) at SLAC National Accelerator Laboratory (USA) was used as showcase for this diagnostic scheme. By applying a combined two-color, multi-photon experiment with polarization control, the degree of circular polarization of the Delta undulator has been determined. Towards this goal, an oriented electronic state in the continuum was created by non-resonant ionization of the O2 1s core shell with circularly polarized FEL pulses at hν ≃ 700 eV. An also circularly polarized, highly intense UV laser pulse with hν ≃ 3.1 eV was temporally and spatially overlapped, causing the photoelectrons to redistribute into so-called sidebands that are energetically separated by the photon energy of the UV laser. By determining the circular dichroism of these redistributed electrons using angle resolving electron spectroscopy and modeling the results with the strong-field approximation, this scheme allows to unambiguously determine the absolute degree of circular polarization of any pulsed, ultraintense XUV or X-ray laser source.

Accurate prediction of X-ray pulse properties from a free-electron laser using machine learning

A. Sanchez-Gonzalez,1 P. Micaelli,1 C. Olivier,1 T. R. Barillot,1 M. Ilchen,2, 3 A. A. Lutman,4 A. Marinelli,4 T. Maxwell,4 A. Achner,3 M. Agåker,5 N. Berrah,6 C. Bostedt,4, 7 J. Buck,8 P. H. Bucksbaum,2, 9 S. Carron Montero,4, 10 B. Cooper,1 J. P. Cryan,2 M. Dong,5 R. Feifel,11 L. J. Frasinski,1 H. Fukuzawa,12 A. Galler,3 G. Hartmann,8, 13 N. Hartmann,4 W. Helml,4, 14 A. S. Johnson,1 A. Knie,13 A. O. Lindahl,2, 11 J. Liu,3 K. Motomura,12 M. Mucke,5 C. O’Grady,4 J-E. Rubensson,5 E. R. Simpson,1 R. J. Squibb,11 C. Såthe,15 K. Ueda,12 M. Vacher,16, 17 D. J. Walke,1 V. Zhaunerchyk,11 R. N. Coffee,4 and J. P. Marangos1 1Department of Physics, Imperial College, London, SW7 2AZ, United Kingdom 2Stanford PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA 3European XFEL GmbH, Holzkoppel 4, 22869 Schenefeld, Germany 4Linac Coherent Light Source, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA 5Department of Physics and Astronomy, Uppsala University, Uppsala, 75120, Sweden 6Department of Physics, University of Connecticut, 2152 Hillside Road, U-3046, Storrs, CT 06269, USA 7Argonne National Laboratory, Lemont, IL 60439, USA 8Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, Hamburg, 22607, Germany 9Department of Physics, Stanford University, 382 Via Pueblo Mall, Stanford, CA 94305, USA 10California Lutheran University, 60 W Olsen Rd, Thousand Oaks, CA 91360, USA 11Department of Physics, University of Gothenburg, Origovägen 6B, 41296 Gothenburg, Sweden 12Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan 13Institut für Physik und CINSaT, Universität Kassel, Heinrich-Plett-Str. 40, 34132 Kassel, Germany 14Physics Department, TU Munich, James-Franck-Str. 1, 85748 Garching, Germany 15MAX IV Laboratory, Lund University, Box 118, SE-221 00 Lund, Sweden 16Department of Chemistry, Imperial College London, London SW7 2AZ, United Kingdom 17Department of Chemistry Ångtröm, Uppsala University, Uppsala, 75120, SwedenFree-electron lasers providing ultra-short high-brightness pulses of X-ray radiation have great potential for a wide impact on science, and are a critical element for unravelling the structural dynamics of matter. To fully harness this potential, we must accurately know the X-ray properties: intensity, spectrum and temporal profile. Owing to the inherent fluctuations in free-electron lasers, this mandates a full characterization of the properties for each and every pulse. While diagnostics of these properties exist, they are often invasive and many cannot operate at a high-repetition rate. Here, we present a technique for circumventing this limitation. Employing a machine learning strategy, we can accurately predict X-ray properties for every shot using only parameters that are easily recorded at high-repetition rate, by training a model on a small set of fully diagnosed pulses. This opens the door to fully realizing the promise of next-generation high-repetition rate X-ray lasers.

Generating circularly polarized radiation in the extreme ultraviolet spectral range at the free-electron laser FLASH

A new device for polarization control at the free electron laser facility FLASH1 at DESY has been commissioned for user operation. The polarizer is based on phase retardation upon reflection off metallic mirrors. Its performance is characterized in three independent measurements and confirms the theoretical predictions of efficient and broadband generation of circularly polarized radiation in the extreme ultraviolet spectral range from 35 eV to 90 eV. The degree of circular polarization reaches up to 90% while maintaining high total transmission values exceeding 30%. The simple design of the device allows straightforward alignment for user operation and rapid switching between left and right circularly polarized radiation.

Emitter-site-selective photoelectron circular dichroism of trifluoromethyloxirane

The angle-resolved inner-shell photoionization of R-trifluoromethyloxirane,

Extreme Ultraviolet to Visible Dispersed Single Photon Detection for Highly Sensitive Sensing of Fundamental Processes in Diverse Samples

{\mathrm{C}}_{3}{\mathrm{H}}_{3}{\mathrm{F}}_{3}\mathrm{O}

Angle resolved photoelectron spectroscopy of two-color XUV-NIR ionization with polarization control.

, is studied experimentally and theoretically. Thereby, we investigate the photoelectron circular dichroism (PECD) for nearly symmetric O

Note: Soft X-ray transmission polarizer based on ferromagnetic thin films

1s

Polarization control in an X-ray free-electron laser

and F

Ultrashort Free-Electron Laser X-ray Pulses

1s

Attosecond time–energy structure of X-ray free-electron laser pulses

electronic orbitals, which are localized on different molecular sites. The respective dichroic