title: Circular dichroism measurements at an x-ray free-electron laser with polarization control.
abstract: 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.
authors: Deutsches Elektronen-Synchrotron, Notkestraße 85, 22607 Hamburg, Germany.
authors: G
authors: G
authors: Hartmann
authors: PULSE at Stanford, 2575 Sand Hill Road, Menlo Park, California 94025, USA.
authors: A O
authors: AO
authors: Lindahl
authors: Institut für Physik, University of Kassel, Heinrich-Plett-Str. 40, 34132 Kassel, Germany.
authors: A
authors: A
authors: Knie
authors: SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA.
authors: N
authors: N
authors: Hartmann
authors: SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA.
authors: A A
authors: AA
authors: Lutman
authors: SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA.
authors: J P
authors: JP
authors: MacArthur
authors: Deutsches Elektronen-Synchrotron, Notkestraße 85, 22607 Hamburg, Germany.
authors: I
authors: I
authors: Shevchuk
authors: European XFEL GmbH, Albert-Einstein-Ring 19, 22761 Hamburg, Germany.
authors: J
authors: J
authors: Buck
authors: European XFEL GmbH, Albert-Einstein-Ring 19, 22761 Hamburg, Germany.
authors: A
authors: A
authors: Galler
authors: SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA.
authors: J M
authors: JM
authors: Glownia
authors: SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA.
authors: W
authors: W
authors: Helml
authors: SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA.
authors: Z
authors: Z
authors: Huang
authors: Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, Moscow 119991, Russia.
authors: N M
authors: NM
authors: Kabachnik
authors: Departamento de Fisica de Materiales, UPV/EHU, Donostia International Physics Center (DIPC), E-20018 San Sebastian/Donostia, Spain.
authors: A K
authors: AK
authors: Kazansky
authors: European XFEL GmbH, Albert-Einstein-Ring 19, 22761 Hamburg, Germany.
authors: J
authors: J
authors: Liu
authors: SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA.
authors: A
authors: A
authors: Marinelli
authors: European XFEL GmbH, Albert-Einstein-Ring 19, 22761 Hamburg, Germany.
authors: T
authors: T
authors: Mazza
authors: SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA.
authors: H-D
authors: HD
authors: Nuhn
authors: Deutsches Elektronen-Synchrotron, Notkestraße 85, 22607 Hamburg, Germany.
authors: P
authors: P
authors: Walter
authors: Deutsches Elektronen-Synchrotron, Notkestraße 85, 22607 Hamburg, Germany.
authors: J
authors: J
authors: Viefhaus
authors: European XFEL GmbH, Albert-Einstein-Ring 19, 22761 Hamburg, Germany.
authors: M
authors: M
authors: Meyer
authors: SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA.
authors: S
authors: S
authors: Moeller
authors: SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA.
authors: R N
authors: RN
authors: Coffee
authors: SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA.
authors: M
authors: M
authors: Ilchen