TUB —  Tuesday - Late Morning   (27-Aug-19   11:00—12:45)
Chair: S. Werin, SLF, Lund, Sweden
Paper Title Page
TUB01 Echo-Enabled Harmonic Generation Lasing of the FERMI FEL in the Soft X-Ray Spectral Region 33
  • P. Rebernik Ribič
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • P. Rebernik Ribič
    University of Nova Gorica, Nova Gorica, Slovenia
  The layout of the FERMI FEL-2 undulator line, normally operated in the two-stage high-gain harmonic generation (HGHG) configuration, was temporarily modified to allow running the FEL in the echo-enabled harmonic generation (EEHG) mode. The EEHG setup produced stable, intense and nearly fully coherent pulses at wavelengths as short as 5.9 nm (211 eV). Comparing the performance to the two-stage HGHG showed that EEHG gives significantly better spectra in terms of the central wavelength stability and bandwidth, especially at high harmonics, where electron-beam imperfections start to play a significant role. Observation of stable, narrow-band, coherent emission down to 2.6 nm (474 eV) indicates the possibility to extend the lasing region to even shorter wavelengths.  
slides icon Slides TUB01 [10.360 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUB01  
About • paper received ※ 21 August 2019       paper accepted ※ 29 August 2019       issue date ※ 05 November 2019  
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Reflection Self-Seeding at SACLA  
  • I. Inoue, T. Harapresenter
    RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
  XFEL are widely operated based on the self-amplified spontaneous emission (SASE) scheme, where spontaneous radiation originating from density modulations in the electron beam is amplified along periodic magnetic field in undulators. Although the SASE scheme effectively produces intense X-ray beams, the stochastic starting-up processes cause poor temporal coherence and a broad spectrum. To narrow the bandwidth while keeping high intensity, we have recently developed an efficient seeding scheme at SACLA, called reflection self-seeding; the SASE-XFEL beam in the first-half undulators is monochromatized via Bragg reflection of a silicon channel-cut crystal, and the monochromatic seed is amplified in the remaining undulators. By applying this scheme to SACLA, we succeeded in producing nearly Fourier-transform-limited XFEL pulses, corresponding to an increase of spectral brightness by a factor of six with respect to the SASE-XFEL [1]. In this presentation, I will talk about the concept of the reflection self-seeding and technical details. Also, I will report on the current operation status and future perspectives of the reflection self-seeding at SACLA.
[1] I. Inoue et al., Nature Photonics 13, 319 (2019)
slides icon Slides TUB02 [49.922 MB]  
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Hard X-Ray Self-Seeding at PAL-XFEL  
  • C.-K. Min, M.H. Cho, H. Heo, H.-S. Kang, C. Kim, G. Kim, M.J. Kim, J.H. Ko, D.H. Na, I.H. Nam, B.G. Oh, S.Y. Rah, C.H. Shim, Y.J. Suh, H. Yang
    PAL, Pohang, Kyungbuk, Republic of Korea
  • K. Kim, D. Shu, Yu. Shvyd’ko
    ANL, Lemont, Illinois, USA
  A hard X-ray self-seeding utilizing time-delayed forward Bragg diffracted photons from thin diamond crystals has been successfully commissioned in a broad spectral range (3.5~14.4 keV), and will be soon provided to user experiments. In the self-seeded mode, the spectral bandwidth is typically 0.2~0.5 eV FWHM in contrast to SASE mode, in which the spectral bandwidth is around 20 eV. This implies that the seeded FEL can be a single longitudinal mode laser since the number of longitudinal mode is 100~200 in the SASE operation. In this case, the photon number of filtered FEL is expected to be fluctuated 100% from the narrow bandwidth filtering out of random and spiky SASE spectra. We found that our energy stability of electron bunches (10-4) do not degrade much the seeding performance and the large variation of the seeded FEL intensity will be from the seeding probability. The advantages of 30 um thin diamond crystal and diagnostic tool for the self-seeding will be also presented.  
slides icon Slides TUB03 [28.431 MB]  
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Generation and Measurement of Intense Few-Femtosecond Superradiant Soft X-Ray Free Electron Laser Pulses  
  • S. Spampinati, E. Allaria, L. Badano, C. Callegari, G. De Ninno, M. Di Fraia, S. Di Mitri, L. Giannessi, N. Mahne, M. Manfredda, N.S. Mirian, G. Penco, O. Plekan, K.C. Prince, L. Raimondi, P. Rebernik Ribič, C. Spezzani, M. Trovò, M. Zangrando
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • R. Feifel, R. Squibb
    Uppsala University, Uppsala, Sweden
  • T. Mazza
    EuXFEL, Hamburg, Germany
  • X. Yang
    BNL, Upton, New York, USA
  Intense FEL VUV and soft X-ray pulses with a time duration of few fs allows to probe ultrafast, out-of equilibrium dynamics or to pump the sample driving new phase transitions in regimes where uniform heating is not depleted by secondary energy decay channels, such as Auger effect [Principi]. Most of the methods proposed to reduce the FEL pulse duration are based on a manipulation of longitudinal electron beam properties such as emittance, beam current, energy spread, trajectory or optical functions. We present an attractive alternative based on the exploitation of the FEL dynamic process itself, driving the FEL amplifier in saturation and superradiance in a cascade of undulators resonant at higher harmonics of an initial seed. At FERMI we have implemented for the first time a multistage superradiant cascade reaching EUV-soft X-ray wavelengths and producing high-power, stable, FEL pulses with a duration of about 5 fs. We report here the analysis of the configuration used and of the characterization of the radiation produced in this regime.  
slides icon Slides TUB04 [3.300 MB]  
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