Author: Zhaunerchyk, V.
Paper Title Page
TUP012 Numerical Simulation of a Super-radiant THz Source Driven by Femtosecond Electron Bunches 374
  • R.V. Chulkov
    B.I. Stepanov Institute of Physics, Belarus, Russia
  • V.A. Goryashko
    Uppsala University, Uppsala, Sweden
  • V. Zhaunerchyk
    University of Gothenburg, Gothenburg, Sweden
  Funding: We would like to acknowledge the financial support from the Swedish FEL center.
Pulsed THz FELs are typically driven by rf Linacs which produce intense electron bunches with a duration of a few picoseconds or even shorter. When the bunch duration is less than a picosecond, the wavelength of the THz light is greater than the bunch length and the FEL operates in the super-radiant (SR) regime*. In the report, we summarize our studies performed for an SR source operating in the THz frequency range. In particular, we focus on an open-type planar undulator comprising no guiding structure. Using a numerical code that supports 3D modeling of the SR dynamics as well as statistical properties of electron bunches, we analyze influence of electron bunch parameters on generated THz radiation and reveal some surprising results. More specifically, for the considered undulator configuration, we predict degradation in the angular divergence and spectral broadening of the generated radiation as the electron bunch emittance decreases. We also demonstrate how electron bunch broadening associated with the electron energy spread can eventually be suppressed.
* R. Chulkov, V. Goryashko, and V. Zhaunerchyk, Report III of the series of reports by the Swedish FEL Center and FREIA Group,
poster icon Poster TUP012 [1.553 MB]  
Influence of the Lower Frequency Branch on the Performance of a Waveguided THz FEL  
  • V.O. Yatsyna, V. Zhaunerchyk
    University of Gothenburg, Gothenburg, Sweden
  • R.T. Jongma, W.J. van der Zande
    Radboud University, Nijmegen, The Netherlands
  Funding: We would like to acknowledge the financial support from Swedish Research Council and Swedish FEL Center.
The Terahertz (THz) frequency range is highly relevant in many applications ranging from medicine to security and communication. Among different available THz sources, free electron lasers (FELs) are the most powerful and versatile sources that provide tunable light in the whole THz region. THz FELs usually operate as oscillators and employ a waveguide to suppress diffraction losses. When a waveguide covers only a part of the optical cavity, substantial drops of the output power at certain wavelengths are observed *. The THz FEL FLARE operating in the wavelength range of 0.1-1.5 mm comprises a waveguide which covers the whole cavity length**. Surprisingly, the spectral gaps are still observed. To get insight into origin of the gaps, we perform numerical simulations taking into account both lower and higher resonant frequency branches, as well as interaction between 150 THz pulses that simultaneously propagate through the FLARE cavity. Simulations predict that the lower frequency branch can hamper amplification of the other branch and, thus, can lead to the spectral gaps.
* R. Prazerez et al. Phys. Rev. ST Accel. Beams 12, 010701 (2009)
** R. Chulkov et al. Multi-Mode Dynamics in a Short-Pulse THz FEL. Phys. Rev. ST Accel. Beams, to be published in 2014
poster icon Poster TUP067 [1.457 MB]  
TUP079 A Swedish Compact Linac-based THz/X-ray Source at FREIA 545
  • V.A. Goryashko
    Private Address, Uppsala, Sweden
  • A. Opanasenko
    NSC/KIPT, Kharkov, Ukraine
  • V. Zhaunerchyk
    University of Gothenburg, Gothenburg, Sweden
  THz radiation enables probing and controlling low-energy excitations in matter such as molecular rotations, DNA dynamics, spin waves and Cooper pairs. In view of growing interest to the THz radiation, the Swedish FEL Center and FREIA Laboratory are working on the conceptual design of a compact multicolor photon source for multidisciplinary research. We present the design of such a source driven by high-brightness electron bunches produced by a superconducting linear accelerator. A THz source is envisioned as an FEL oscillator since this enables not only generation of THz pulses with a bandwidth down to 0.01% (with inter-pulse locking technique) but also generation of short pulses with several cycles in duration by detuning the resonator. For pump-probe experiments, the THz source will be complemented with an X-ray source. One of the most promising options is the inverse Compton scattering of quantum laser pulses from electron bunches. Such an X-ray source will operate in water window with output intensity comparable to a second generation synchrotron. The envisioned THz/X-ray source is compact with a cost comparable to the cost of one beamline at a synchrotron.  
Scanning Problems of FLARE, a THz-FEL Waveguide  
  • R.T. Jongma, D. Arslanov, M.A. Vermeulen, A.F.G. van der Meer
    Radboud University, Nijmegen, The Netherlands
  • M. Fujimoto
    ISIR, Osaka, Japan
  • V.O. Yatsyna
    University of Gothenburg, Gothenburg, Sweden
  • V. Zhaunerchyk
    Uppsala University, Uppsala, Sweden
  Funding: FLARE is part of the NCAS project funded through the “Big Facilities” programme of the Netherlands Organisation for Scientific Research (NWO).
The (0.2 – 3) THz free-electron laser FLARE is equipped with a waveguide extending over the full cavity length. Therefore, the tuning gaps observed in the long-wavelength range of FELIX, FELBE and CLIO, which were attributed to mode-conversion at the waveguide free-space transitions, are avoided. Unfortunately, an even more severe scanning problem is observed and continuous tuning of the photon energy is up to this moment impossible. The origin of this problem is not yet understood and experiments to gain insight into the problem are ongoing. We have investigated the (coherent) spontaneous emission as a function of wavelength, the gain build-up in the vicinity of tuning gaps, and the operation at a micro-pulse repetition frequency at which only a single photon bunch circulates in the cavity. The latter is explored to investigate if the low-frequency mode (the slow wave) that can also build up in a wave-guided cavity and travels at lower group velocity than the electron bunches, interferes with the efficient power build-up of the desired high-frequency mode in the trailing bunches. Status and results of the experiments will be discussed.
poster icon Poster TUP065 [4.287 MB]  
Prospects of Stimulated X-ray Raman Scattering with Free-Electron Laser Sources  
  • N. Rohringer, V. Kimberg, C. Weninger
    Max Planck Institute for the Physics of Complex Systems, Dresden, Germany
  • M. Agaker, R. Feifel, M. Mucke, J. Nordgren, J.E. Rubensson, C. Sathe, R. Squibb, V. Zhaunerchyk
    Uppsala University, Uppsala, Sweden
  • C. Bostedt, J.D. Bozek, S. Carron Montero, R.N. Coffee, J. Krzywinski, A. Lindahl, A. Lutmann, T.J. Maxwell
    SLAC, Menlo Park, California, USA
  • B. Erk, D. Rolles
    DESY, Hamburg, Germany
  • M. Ilchen
    XFEL. EU, Hamburg, Germany
  • T. Kierspel, J. Küpper, T.G. Mullins
    University of Hamburg, Hamburg, Germany
  • O.D. Mücke
    CFEL, Hamburg, Germany
  • M. Purvis, J.J. Rocca, D.P. Ryan
    CSU, Fort Collins, Colorado, USA
  • A. Sanchez-Gonzalez
    Imperial College of Science and Technology, Department of Physics, London, United Kingdom
  XFELs might open the pathway to transfer non-linear spectroscopic techniques to the x-ray domain, to study electron motion at unprecedented time and length scales. A promising x-ray pump probe technique is based on stimulated electronic x-ray Raman scattering. I will present the first experimental demonstration of stimulated electronic x-ray Raman scattering in a gas sample of neon*. Despite the limited spectral coherence of SASE XFELs, high-resolution spectra can be obtained by statistical methods, opening the path to coherent stimulated x-ray Raman spectroscopy. An extension of these ideas to molecules** and the results of a recent experiment in CO will be discussed. The high-gain regime, involving exponential amplification and strong-field effects will be contrasted to stimulated scattering at moderate x-ray intensities, more appropriate for spectroscopic studies. A critically assessment of the feasibility of nonlinear x-ray spectroscopic techniques and requirements on the stability and pulse parameters of XFEL sources that could enable these new techniques, will be presented.
* C. Weninger et al., Phys. Rev. Lett. 111, 233902 (2013)
** C. Weninger and N. Rohringer, Phys Rev A 88, 053421 (2013)
slides icon Slides FRA01 [3.771 MB]