Author: Franz, P.L.
Paper Title Page
Development of Two-Color Sub-Femtosecond Pump/Probe Techniques with X-Ray Free-Electron Lasers  
  • Z.H. Guo, P.L. Franz
    Stanford University, Stanford, California, USA
  • D.B. Cesar, J.P. Cryan, T.D.C. Driver, J.P. Duris, Z. Huang, K. Larsen, S. Li, A. Marinelli, J.T. O’Neal, R. Robles, N.S. Sudar, A.L. Wang, Z. Zhang
    SLAC, Menlo Park, California, USA
  Funding: This work is supported by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences (BES), Accelerator and Detector research program.
We report the generation of GW-level attosecond pump/probe pulse pairs with tunable sub-femtosecond delays at the Linac Coherent Light Source (LCLS). The attosecond 370 eV pump pulse is first generated via the Enhanced Self-Amplified Spontaneous Emission (ESASE) method, then the attosecond 740 eV probe pulse is produced by re-amplifying the electron beam microbunching after the magnetic chicane. Due to the harmonic amplification, the minimal delay between pump-probe pulse pairs (limited by slippage between the light field and the electron bunch) can be shorter than 1 femtosecond. We use the angular streaking technique to measure temporal delays between pump/probe pulse pairs at multiple beamline configurations. When the delay chicane is turned off, the averaged delay is increased by ~150 attoseconds by adding one undulator module for probe pulses. Long delays can be set up by turning the delay chicane on. These experimental results are in agreement with start-to-end XFEL simulations. Looking toward future experiments, our sub-femtosecond pump/probe technique can be applied to observe electronic charge dynamics in molecular systems.
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Multiobjective Optimization of the LCLS-II Photoinjector  
  • N.R. Neveu
    SLAC, Menlo Park, California, USA
  • T.H. Chang, S.T.P. Hudson, J.M. Larson
    ANL, Lemont, Illinois, USA
  • P.L. Franz
    Stanford University, Stanford, California, USA
  Genetic algorithms and particle swarm optimization are currently the most widely used optimization algorithms in the accelerator physics community. These algorithms can take many evaluations to find optimal solutions for one machine prototype. In this work, the LCLS-II photoinjector is optimized with three optimization algorithms: a genetic algorithm, a surrogate based algorithm, and a multi-start scalarization method. All three algorithms were able to optimize the photoinjector, with various trade-offs for each method discussed here.  
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