# FS-FLASH-O

 2020-01-1314:26 [PUBDB-2020-00139] Journal Article et al Time-Resolved Dissociation Dynamics of Iodomethane Resulting from Rydberg and Valence Excitation Rydberg excitations in the vacuum ultraviolet spectral range may open upmolecular photoreaction pathways not accessible from lower-lying valence states. Here,single-shot UV/VUV pump−probe spectroscopy was used to study the photodissociationdynamics of iodomethane after 268 nm excitation in the A-band and excitation of the 6p(2E3/2) Rydberg state at 161 nm. [...] Restricted: PDF PDF (PDFA); 2019-11-1415:58 [PUBDB-2019-04226] Contribution to a conference proceedings et al Two-Color Operation of FLASH2 Undulator 39th International Free-Electron Laser Conference, FEL19, HamburgHamburg, Germany, 26 Aug 2019 - 30 Aug 2019 Geneva : JACoW, CERN TUP055 (2019) FLASH is the first soft X-ray FEL user facility, routinely providing brilliant photon beams for users since 2005. The second undulator branch of this facility, FLASH2, is gap-tunable which allows to test and use advanced lasing concepts. [...] External link: Fulltext 2019-10-1612:35 [PUBDB-2019-03691] Journal Article et al Strong-Field Extreme-Ultraviolet Dressing of Atomic Double Excitation Physical review letters 123(16), 163201 (2019) [10.1103/PhysRevLett.123.163201]   We report on the experimental observation of a strong-field dressing of an autoionizing two-electronstate in helium with intense extreme-ultraviolet laser pulses from a free-electron laser. The asymmetricFano line shape of this transition is spectrally resolved, and we observe modifications of the resonanceasymmetry structure for increasing free-electron-laser pulse energy on the order of few tens of Microjoules.A quantum-mechanical calculation of the time-dependent dipole response of this autoionizing state, drivenby classical extreme-ultraviolet (XUV) electric fields, evidences strong-field-induced energy and phaseshifts of the doubly excited state, which are extracted from the Fano line-shape asymmetry. [...] OpenAccess: PDF PDF (PDFA); 2019-09-2311:19 [PUBDB-2019-03424] Journal Article et al Nonlinear Coherence Effects in Transient-Absorption Ion Spectroscopy with Stochastic Extreme-Ultraviolet Free-Electron Laser Pulses Physical review letters 123(10), 103001 (2019) [10.1103/PhysRevLett.123.103001]   We demonstrate time-resolved nonlinear extreme-ultraviolet absorption spectroscopy on multiply charged ions, here applied to the doubly charged neon ion, driven by a phase-locked sequence of two intense free-electron laser pulses. Absorption signatures of resonance lines due to $2p-3d$ bound–bound transitions between the spin-orbit multiplets $^3P_{0,1,2}$ and $^3D_{1,2,3}$ of the transiently produced doubly charged Ne$^{2+}$ ion are revealed, with time-dependent spectral changes over a time-delay range of (2.4±0.3) fs. [...] OpenAccess: PDF PDF (PDFA); 2019-09-2310:57 [PUBDB-2019-03423] Journal Article et al Tracing charge transfer in argon dimers by XUV-pump IR-probe experiments at FLASH The journal of chemical physics 151(8), 084314 - (2019) [10.1063/1.5116234]   Charge transfer (CT) at avoided crossings of excited ionized states of argon dimers is observed using a two-color pump-probe experiment at the free-electron laser in Hamburg (FLASH). The process is initiated by the absorption of three 27-eV-photons from the pump pulse, which leads to the population of Ar2+*–Ar states. [...] Published on 2019-08-30. Available in OpenAccess from 2020-08-30.: PDF PDF (PDFA); 2019-09-1919:02 [PUBDB-2019-03416] Journal Article/Contribution to a conference proceedings et al Intensity-dependent near-threshold ionization of Kr in the vacuum-uv International Conference on Spectral Lines Shapes, DublinDublin, Ireland, 17 Jun 2018 - 22 Jun 2018   In this work, we present measurements of the intensity-dependent photoelectron spectrum of Kr irradiated by the FLASH FEL tuned to a photon energy of 25.8 eV. Intensity dependent photoelectron spectra were obtained with the aid of a Velocity Map Imaging (VMI) spectrometer. [...] OpenAccess: PDF PDF (PDFA); 2019-07-1210:44 [PUBDB-2019-02698] Journal Article et al Evidence of Extreme Ultraviolet Superfluorescence in Xenon Physical review letters 123(2), 023201 (2019) [10.1103/PhysRevLett.123.023201]   We present a comprehensive experimental and theoretical study on superfluorescence in the extreme ultraviolet wavelength regime. Focusing a free-electron laser pulse in a cell filled with Xe gas, the medium is quasi-instantaneously population inverted by 4d-shell ionization on the giant resonance followed by Auger decay [...] OpenAccess: PDF PDF (PDFA); 2019-07-0916:47 [PUBDB-2019-02678] Journal Article et al Wavefront-propagation simulations supporting the design of a time-delay compensating monochromator beamline at FLASH2 Journal of synchrotron radiation 26(3), 899 - 905 (2019) [10.1107/S160057751900345X]   Wavefront-propagation simulations have been performed to complete the design of a monochromator beamline for FLASH2, the variable-gap undulator line at the soft X-ray free-electron laser in Hamburg (FLASH). Prior to propagation through the beamline optical elements, the parameters of the photon source were generated using the GENESIS code which includes the free-electron laser experimental data. [...] OpenAccess: PDF PDF (PDFA); Restricted: PDF PDF (PDFA); 2019-06-2110:30 [PUBDB-2019-02527] Journal Article et al Two-color XUV+NIR femtosecond photoionization of neon in the near-threshold region New journal of physics 21(6), 063034 (2019) [10.1088/1367-2630/ab2a98]   Results of angle-resolved electron spectroscopy of near-threshold photoionization of Ne atoms bycombined femtosecond extreme ultraviolet and near infraredfields are presented. The dressed-electron spectra show an energetic distribution into so-called sidebands, being separated by thephoton energy of the dressing laser [...] OpenAccess: PDF PDF (PDFA); 2019-05-2911:54 [PUBDB-2019-02388] Journal Article et al An X-ray gas monitor for free-electron lasers Journal of synchrotron radiation 26(4), 1092 - 1100 (2019) [10.1107/S1600577519005174]   A novel X-ray gas monitor (XGM) has been developed which allows the measurement of absolute photon pulse energy and photon beam position at all existing and upcoming free-electron lasers (FELs) over a broad spectral range covering vacuum ultraviolet (VUV), extreme ultraviolet (EUV) and soft and hard X-rays. The XGM covers a wide dynamic range from spontaneous undulator radiation to FEL radiation and provides a temporal resolution of better than 200 ns [...] OpenAccess: PDF PDF (PDFA);