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Shimada, M.

Paper Title Page
TUPPH007 Spatial Coherence Measurement of UVSOR-II Free Electron Laser  
 
  • O. V. Chubar, M.-E. Couprie
    SOLEIL, Gif-sur-Yvette
  • K. Fukui
    University of Fukui, Fukui
  • M. Hosaka
    Nagoya University, Nagoya
  • M. Katoh, A. Mochihashi, M. Shimada
    UVSOR, Okazaki
  • G. Lambert
    RIKEN Spring-8, Hyogo
  • M. Labat
    CEA, Gif-sur-Yvette
 
  The well defined phase relationship of coherent radiation is wished for a large number of experiments. The advent of very small emittance electron beams allowed improvement of the transverse coherence of the undulators radiation and lead to extensive use of modern synchrotron facilities in the visible to x-ray domain. Nevertheless, Free Electron Lasers (in particular in the seeded Coherent Harmonic Generation (CHG) scheme) may offer additional capabilities such as shorter pulse duration, smaller spectral bandwidth, higher peak power and improved transverse coherence. Transverse coherence of the third Coherent Harmonic has been studied on the UVSOR-II storage ring (Japan) at 600 MeV, using a 2.5 mJ, 1 kHz, 1.2 ps Ti:Sa laser at 800 nm wavelength with the double slit method. The improvement of the transverse coherence of the FEL radiation compared to spontaneous emission is shown via the visibility of the interference pattern resulting from double slits. The experimental results are compared to analytical calculations as well as to 3D FEL and wavefront propagation simulations performed with SRW.  
TUPPH008 Beam Dynamics Studies on the UVSOR-II Free Electron Laser 236
 
  • M.-E. Couprie
    SOLEIL, Gif-sur-Yvette
  • M. Hosaka
    Nagoya University, Nagoya
  • M. Katoh, A. Mochihashi, M. Shimada
    UVSOR, Okazaki
  • G. Lambert
    RIKEN Spring-8, Hyogo
  • M. Labat
    CEA, Gif-sur-Yvette
 
  In the Coherent Harmonic Generation Free Electron Laser configuration, an external laser source is seeded inside a first undulator. The interaction between the electron beam and this seed induces energy modulation of the bunch, further converted into a density modulation, producing coherent radiation in a second undulator. The energy modulation enhances the energy spread of the electron bunch, converted by the machine optics into a modification of its longitudinal distribution. In the case of a storage ring FEL, the electrons are re-circulating: the same bunch keeps interacting with the seeded laser, and relaxation of the distribution is only allowed in between two laser injections. Such specific dynamics has been studied on the CHG FEL of UVSOR-II storage ring (Japan). The electron beam stored at 600 MeV is seeded using a 2.5 mJ, 1 kHz, 1.2 ps Ti:Sa laser at 800 nm wavelength, allowing radiation at 266 nm (third harmonic). A Streak Camera is used to record the evolution of the longitudinal profiles as a function of the repetition rate and average power of the seeding laser, leading to bunch lengthening and distortion dynamical analysis. It appeared that because the heating induced by the interaction remains local, the refreshment process of the electronic distribution is modified. The experimental results are compared to simulations using SYNC.  
TUCAU02 Even Harmonic Generation on UVSOR-II Storage Ring  
 
  • M.-E. Couprie
    SOLEIL, Gif-sur-Yvette
  • M. Hosaka
    Nagoya University, Nagoya
  • M. Katoh, A. Mochihashi, M. Shimada
    UVSOR, Okazaki
  • G. Lambert
    RIKEN Spring-8, Hyogo
  • M. Labat
    CEA, Gif-sur-Yvette
 
  In the Coherent Harmonic Generation Free Electron Laser configuration, the electrons act as a non-linear medium radiating harmonics of a seed source (e.g., a laser). In the two-step seeding scheme, the seed field forces an energy modulation on the electron bunch in a modulator, converted into a density modulation as the electron beam travels through a dispersive section. Finally, in the radiator, the microbunched electron beam can emit coherently at the fundamental and the harmonics of the seed source. In this paper, successful even harmonic generation is reported on the CHG UV-FEL of UVSOR-II storage ring (Japan) at 600 MeV, using a 2.5 mJ, 1 kHz, 1.2 ps Ti:Sa laser at 800 nm. Second and fourth harmonics were generated using planar configuration of the undulators, and second harmonic was generated in helical configuration, in addition to already observed and studied third coherent harmonic. Such preliminary results allow attractive perspectives to understand further even harmonic generation process, still discussed among the FEL community: in single pass non-guided FELs, with planar undulators even harmonics are expected to vanish on-axis, a spectral selection that could be avoided with helical undulators.  
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