THOB —  FEL Experiments II   (25-Aug-11   10:30—12:00)
Chair: B. Faatz, DESY, Hamburg, Germany
Paper Title Page
THOBI1
 Polarization Control Experiences in Single-pass Seeded FELs  
 
  • C. Spezzani
    ELETTRA, Basovizza, Italy
  
  The design of FERMI@Elettra, being based on APPLE type undulators, allows a straightforward tuning of the polarization of the emitted radiation. The possibility to perform polarization-dependent experiments has been confirmed from the very first phases of FERMI’s commissioning. Moreover, at the seeded storage-ring FEL test facility installed at Elettra, which also relies on an APPLE-based optical klystron, we have measured the Stokes' parameters of coherent harmonic emission and demonstrated that the polarization tunability can be maintained also in the so-called non-linear harmonic generation regime. This result definitely extends the scientific opportunities offered by FERMI@Elettra and concretize the idea of reducing the minimum accessible wavelength at which polarization can be controlled down to the spectral range that matters for transition metal magnetism studies. After a brief discussion about the importance of polarization tunability on FEL light sources, we will review the present status of FEL projects aiming to achieve polarization control and we will present the most recent results obtained at FERMI@Elettra and at the storage-ring FEL of Elettra.  
slides icon Slides THOBI1 [8.326 MB]  
 
THOB2 Advanced Beam Dynamics Experiments at SPARC 451
 
  • A. Bacci, D. Alesini, M. Bellaveglia, M. Castellano, E. Chiadroni, G. Di Pirro, A. Drago, M. Ferrario, A. Gallo, G. Gatti, A. Ghigo, E. Pace, A.R. Rossi, C. Vaccarezza
    INFN/LNF, Frascati (Roma), Italy
  • A. Cianchi
    Università di Roma II Tor Vergata, Roma, Italy
  • M. Del Franco, L. Giannessi, A. Petralia, M. Quattromini, C. Ronsivalle, V. Surrenti
    ENEA C.R. Frascati, Frascati (Roma), Italy
  • S. Lupi
    Coherentia, Naples, Italy
  • B. Marchetti
    INFN-Roma II, Roma, Italy
  • A. Mostacci, L. Palumbo
    Rome University La Sapienza, Roma, Italy
  • V. Petrillo
    Universita' degli Studi di Milano, Milano, Italy
  • L. Serafini
    Istituto Nazionale di Fisica Nucleare, Milano, Italy
  • M. Serluca
    INFN-Roma, Roma, Italy
  
  The successful operation of the SPARC injector in the Velocity Bunching (VB) mode (bunches with 1 kA current with emittance of 3 mm-mrad have been produced) has opened new perspectives to conduct advanced beam dynamics experiments with ultra-short electron pulses able to extend the THz spectrum or to drive the FEL in the SASE Single Spike mode. A new technique called Laser Comb, able to generate a train of short pulses with high repetition rate, has been extensively tested in the VB configuration. Two electron beam pulses 300 fs long separated by 1 ps have been characterized and the spectrum produced by the SASE interaction has been observed, showing that both pulses have been correctly matched to the undulator and were both lasing. In this paper we report the experimental and theoretical results obtained so far.  
slides icon Slides THOB2 [6.673 MB]  
 
THOB3 First Demonstration of a Slippage-dominant Superradiant Free-electron Laser Amplifier 455
 
  • X. Yang, Y. Hidaka, B. Podobedov, S. Seletskiy, Y. Shen, X.J. Wang
    BNL, Upton, Long Island, New York, USA
  
  We report the first experimental demonstration of a slippage-dominant superradiant free-electron laser (FEL) using an ultrafast seed-laser pulse. We measured the evolution of the longitudinal phase space in the slippage-dominant superradiant regime, and also the output spectrum and pulse energy versus the electron beam energy. With a ±1% variation in the electron beam energy, we observed a seed-like fully longitudinal coherence, and ±2% spectral tuning range. The temporal and spectral evolution of the slippage-dominant FEL radiation as predicted by a numerical simulation was experimentally verified for the first time.  
slides icon Slides THOB3 [0.374 MB]  
 
THOB4 Transverse Coherence and Polarization Measurement of Coherent Femtosecond Pulses from a Seeded FEL 458
 
  • J. Schwenke, N. Čutić, F. Lindau, S. Werin
    MAX-lab, Lund, Sweden
  • E. Mansten
    Lund University, Division of Atomic Physics, Lund, Sweden
  
  We report on measurements of the transverse coherence and polarization of light pulses at 131 nm generated by a seeded free-electron laser. Our setup consists of two undulators. The first undulator is used to energy modulate relativistic electron bunches (375 MeV) with the help of an ultraviolet seed laser pulse at 263 nm. The electron bunches subsequently pass through a dispersive section, where the energy modulation is converted into microbunching, and then enter the radiator undulator. The radiator is an APPLE-II type undulator set to be in resonance for 131 nm radiation. The radiator emits coherent femtosecond pulses up to the 6th harmonic of the seed laser [1]. The state of polarization of the pulses can be tuned from planar to helical polarization by shifting the undulator magnets. The emitted pulses are analyzed with a grating spectrometer. A double slit aperture is positioned in the beam in order to determine the transverse coherence of the light pulses by analyzing the fringe visibility. Furthermore, the generation of circular polarized light is demonstrated. The polarization state of the light pulses is measured with a Rochon prism polarizer.
[1] Cutic et al, Phys. Rev. Spec. Top-AC 14, 030706 (2011) 		 
slides icon Slides THOB4 [1.173 MB]  
 
THOB5 FEL Spectral Measurements at LCLS 461
 
  • J.J. Welch, F.-J. Decker, Y.T. Ding, P. Emma, A.S. Fisher, J.C. Frisch, Z. Huang, R.H. Iverson, H. Loos, M. Messerschmidt, H.-D. Nuhn, D.F. Ratner, J.L. Turner, J. Wu
    SLAC, Menlo Park, California, USA
  
  Funding: Work supported in part by the DOE Contract DE-AC02-76SF00515.
Control and knowledge of the spectrum of FEL X-ray radiation at the LCLS is important to the quality and interpretation of experimental results. Narrow bandwidth is useful in experiments requiring high-brightness beams. Wide bandwidth is particularly useful for photon energy calibration using absorption spectra. Since LCLS was commissioned in 2009 measurements have been made of average and single shot spectra of X-ray FEL radiation at the LCLS over a range of 800 to 8000 eV, for fundamental and harmonic radiation. These include correlations with chirp, bunch current, undulator K-taper, electron beam energy, and charge as well as some specialized machine configurations. In this paper we present results and discuss the relationship of the electron beam energy distribution to the observed X-ray spectrum. 		 
slides icon Slides THOB5 [0.442 MB]