TUB —  Seeded FELs   (25-Aug-15   10:30—12:00)
Paper Title Page
TUB01
 Spectro-Temporal Control and Characterization of XUV Pulses from a Seeded Free-Electron Laser  
 
  • D. Gauthier, E. Allaria, P. Cinquegrana, M.B. Danailov, G. De Ninno, A.A. Demidovich, E. Ferrari, L. Giannessi, G. Penco, P. Rebernik Ribič, P. Sigalotti
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • G. De Ninno
    University of Nova Gorica, Nova Gorica, Slovenia
  • E. Ferrari
    Università degli Studi di Trieste, Trieste, Italy
  • L. Giannessi
    ENEA C.R. Frascati, Frascati (Roma), Italy
  • B. Mahieu
    LOA, Palaiseau, France
  
  In ultrafast X-ray science, the knowledge of and the ability to control the spectro-temporal properties of individual X-ray pulses, such as those from free-electron lasers (FELs), constitute a fundamental aspect in the design of new experiments aimed at probing matter with femtosecond temporal resolution. Recent works carried out at the seeded free-electron laser FERMI in Trieste demonstrate that such a device is able to generate light pulses in the XUV spectral region, whose spectro-temporal content can be precisely controlled. These examples rely on the manipulation of the seed laser used as coherent input signal to drive the FEL process. The first experiment demonstrates the phase control of the FEL output pulse through the manipulation of the seed laser frequency chirp. The second is the implementation of a single-shot method for complete pulse characterization. These experiments show not only the first direct evidence of the temporal coherence and the generation of Fourier limited pulses, but they demonstrate the ability to control and shape the spectro-temporal content of the pulses. Consequently, a seeded FEL can be really considered as a laser-like source providing high peak power light pulses. A fine tuning of the light pulses opens the door to new kinds of experiments in the field of coherent nonlinear optics and coherent quantum control.  
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TUB02 Distributed Seeding for Narrow-band X-ray Free-Electron Lasers 301
 
  • D.C. Nguyen, P.M. Anisimov, C.E. Buechler, Q.R. Marksteiner
    LANL, Los Alamos, New Mexico, USA
  
  Funding: We thank Bruce Carlsten, John Lewellen, Steve Russell, and Rich Sheffield (LANL), Craig Ogata and Yuri Shvyd'ko (ANL) for helpful discussion, and the MaRIE project for financial support.
The MaRIE XFEL is the proposed XFEL driven by a 12-GeV electron beam to generate coherent 42-keV photons based on a new seeding technique called distributed seeding (DS). This paper presents details of the distributed seeding technique using Si(111) Bragg crystals as the spectral filters. DS differs from self-seeding in three important aspects. First, DS relies on spectral filtering of the undulator radiation at more than one location early in the exponential gain curve. This leads to an FEL output that is dominated by the coherent seed signal, not SASE noise. Secondly, DS affords the ability to select a wavelength longer than the peak of the SASE gain curve, which leads to improved spectral contrast of the seeded FEL over the SASE background. Lastly, the power growth curves in successive DS stages exhibit the behavior of an FEL amplifier, i.e. a lethargy region followed by the exponential growth region. This behavior results in FEL output pulses that are less spiky than the SASE pulses. Using 3D Genesis simulations, we show that DS with two filters provides a 12X enhancement in spectral brightness relative to SASE and that DS with three filters produces negligible SASE background. The DS FEL spectrum has a relative spectral bandwidth (FWHM) of 8 X 10-5 with about 9 spectral modes. 		 
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TUB03
 Generating Femtosecond to Sub-Femtosecond X-Rays with a Modulated Chirped Beam in a Self-Seeded FEL  
 
  • S. Huang
    PKU, Beijing, People's Republic of China
  • Y. Ding, Z. Huang, G. Marcus
    SLAC, Menlo Park, California, USA
  
  We propose a scheme to generate ultrashort soft X-ray pulses in a self-seeded FEL. In this scheme, a time-energy chirped electron beam is first modulated by an infrared laser with the wavelength of a few microns. It is then used to drive the self-seeded FEL. During the selfseeding section, besides the regular functions of the self-seeding chicane and the grating monochromator, the chicane is also used to shear the previously modulated electron beam, leading to current spikes in the temporal profile. Since the seeded pulse length from the chirped beam is much shorter than the electron bunch, we can choose to align the seed with one of the current spikes for generating a single short pulse. Simulations indicate that soft X-ray pulses with a fwhm of less than 1 fs and peak power at 10 GW level can be obtained.  
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TUB04
 Influence of a Non-Uniform Longitudinal Heating on High Brightness Electron Beams for FEL  
 
  • E. Ferrari
    Università degli Studi di Trieste, Trieste, Italy
  • E. Allaria, M.B. Danailov, G. De Ninno, S. Di Mitri, D. Gauthier, L. Giannessi, G. Penco, E. Roussel, M. Veronese
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • G. De Ninno, D. Gauthier
    University of Nova Gorica, Nova Gorica, Slovenia
  • L. Giannessi
    ENEA C.R. Frascati, Frascati (Roma), Italy
  
  Laser-heater systems are essential tools to control and optimize high-gain free electron lasers (FELs), working in the x-ray wavelength range. Indeed, these systems induce a controllable heating of the energy spread of the electron bunch. The heating allows in turn to suppress longitudinal microbunching instabilities limiting the FEL performance. In this communication, we show that a long-wavelength energy modulation of the electron beam induced by the laser heater can be preserved until the beam entrance in the undulators, affecting the FEL emission process. This non-uniform longitudinal heating can be exploited to investigate the electron- beam microbunching in the linac, as well as to control the FEL spectral properties. Here, we present experimental, analytical and numerical studies carried out at FERMI.  
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TUB05 Tunable High-power Terahertz Free-Electron Laser Amplifier 305
 
  • G. Zhao, S. Huang, K.X. Liu, W. Qin, L. Zeng
    PKU, Beijing, People's Republic of China
  • C.H. Chen, Y.C. Chiu, Y.-C. Huang
    NTHU, Hsinchu, Taiwan
  
  In the THz spectrum, radiation sources are relatively scarce. Although recent advancement on optical technologies has enabled THz radiation generation covering a broad spectral range, free-electron laser (FEL) continues to be the most importance source for generating high-power THz radiation. Here we present an ongoing collaboration between Peking University (PKU) and National Tsinghua University (NTHU) to demonstrate high peak and average powers from a THz free-electron laser amplifier driven by a superconducting accelerator system at PKU. The superconducting accelerator comprises the DC-SRF photoinjector and a linac utilizing two 1.3 GHz Tesla-type cavities. It is expected to deliver high repetition rate electron beam with the energy of 10-25 MeV and rms bunch length of about 3 ps. The driver laser of the photoinjector is a mode-locked frequency-quadrupled Nd:YVO4 laser at 266 nm. We use the remaining gun driver laser power at 1064 nm to pump a THz parametric amplifier (TPA) which designed at NTHU and generate the THz seed radiation for the FEL amplifier. The signal laser of the TPA is tunable over 2 THz, permitting generation of radiation between 0.5 and 2.5 THz to seed the FEL amplifier. With our design parameters and computer simulation in GENESIS, we expect to generate narrow-band, wavelength-tunable THz radiation with sub-MW peak power and Watt-level average power.  
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