Author: Coffee, R.N.
Paper Title Page
TUB01 Seeding Experiments and Seeding Options for LCLS II 1
  • E. Hemsing, R.N. Coffee, W.M. Fawley, Y. Feng, B.W. Garcia, J.B. Hastings, Z. Huang, G. Marcus, D.F. Ratner, T.O. Raubenheimer
    SLAC, Menlo Park, California, USA
  • G. Penn, R.W. Schoenlein
    LBNL, Berkeley, California, USA
  We discuss the present status of FEL seeding experiments toward the soft x-ray regime and on-going studies on possible seeding options for the high repetition soft x-ray line at LCLS-II. The seeding schemes include self-seeding, cascaded HGHG, and EEHG to reach the 1-2 nm regime with the highest possible brightness and minimal spectral pedestal. We describe relevant figures of merit, performance expectations, and potential issues.  
Characterizing Sub-Femtosecond X-ray Pulses from the Linac Coherent Light Source  
  • S. Li, R.N. Coffee, J. Cryan, K.H. Hegazy, Z. Huang, A. Marinelli, A. Natan, T. Osipov, D. Ray
    SLAC, Menlo Park, California, USA
  • G. Guo
    Stanford University, Stanford, California, USA
  The development of sub-femtosecond x-ray capabilities at the Linac Coherent Light Source requires the implementation of time-domain diagnostics with attosecond (as) time resolution. Photoelectrons created by attosecond duration x-ray pulses in the presence of a strong-laser field are known to suffer an energy spread which depends on the relative phase of the strong-laser field at the time of ionization. This phenomenon can be exploited to measure the duration of these ultrashort x-ray pulses. We present an implementation which employs a circularly polarized infrared laser pulse and novel velocity map imaging design which maps the phase dependent momentum of the photoelectron onto a 2-D detector. In this paper, we present the novel co-linear VMI design, simulation of the photoelectron momentum distribution, and the reconstruction algorithm.  
poster icon Poster WEP060 [1.256 MB]  
Fresh-Slice X-Ray Free Electron Laser Schemes for Advanced X-Ray Applications  
  • A.A. Lutman, R.N. Coffee, Y. Ding, J.P. Duris, M.W. Guetg, Z. Huang, J. Krzywinski, J.P. MacArthur, A. Marinelli, T.J. Maxwell, S.P. Moeller, J. Zemella
    SLAC, Menlo Park, California, USA
  • N. Berrah
    University of Connecticut, Storrs, Connecticut, USA
  • C. Emma
    UCLA, Los Angeles, USA
  Funding: This work was supported by Department of Energy contract nos DE-AC02-76SF00515 and DE-SC0012376
The novel fresh-slice XFEL scheme grants control on the temporal slice of the electron bunch lasing in each undulator section. The technique relies on a time-dependent electron bunch trajectory impressed by the transverse wakefield of a corrugated structure and subsequent orbit manipulation in the undulator section. Fully saturated double pulses are produced in two different undulator sections. The wavelength of each pulse is controlled by the undulator magnetic strength and the delay between the pulses can be scanned from a few femtosecond advance of the pulse generated on the bunch head in the second section to a picosecond delay provided by the magnetic chicane. Three-color saturated pulses are demonstrated by using three undulator sections and the polarization of the pulse generated in the last section can be controlled by the variable polarization Delta undulator. In this work we also show the early results for the first multi-stage amplification scheme, producing ultra-short single-pulses with a 100-GW power level in the soft X-rays. The multi-stage amplification is also demonstrated to improve the performance in power and pulse duration control for the two-color FEL scheme.