Author: Hemsing, E.
Paper Title Page
Towards the Demonstration of Soft X-Ray Echo-Enabled Harmonic Generation at Fermi  
  • E. Allaria, R. Bracco, D. Castronovo, I. Cudin, M.B. Danailov, G. De Ninno, S. Di Mitri, B. Diviacco, W.M. Fawley, M. Ferianis, L. Giannessi, M. Lonza, G. Penco, P. Rebernik Ribič, E. Roussel, S. Spampinati, C. Spezzani, L. Sturari, M. Svandrlik, M. Veronese, R. Visintini, M. Zaccaria, D. Zangrando
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • H.-H. Braun, E. Prat, S. Reiche
    PSI, Villigen PSI, Switzerland
  • G. De Ninno
    University of Nova Gorica, Nova Gorica, Slovenia
  • B.W. Garcia, J.B. Hastings, E. Hemsing, T.O. Raubenheimer, G. Stupakov, J.J. Welch
    SLAC, Menlo Park, California, USA
  • G. Penn
    LBNL, Berkeley, California, USA
  • E. Roussel
    SOLEIL, Gif-sur-Yvette, France
  • A. Zholents
    ANL, Argonne, Illinois, USA
  The echo-enabled harmonic generation seeding scheme is based on an echo mechanism that develops in the electron beam phase-space interacting with two seed lasers before and after a strong dispersive region. It has been proposed for extending the capabilities of externally seeded free electron lasers to reach short wavelengths. After the original proposal, a few experiments have confirmed the capabilities of efficient bunching generation at very high harmonics. However, up to now none of the experiments demonstrated FEL amplification from high harmonic bunching produced at 10 nm wavelengths or shorter. In this work, we report about our plans for performing an EEHG experiment at FERMI. The experiment will be done at the FEL-2 line normally operated in the double stage high-gain harmonic generation configuration in the wavelength range 20-4 nm. After the modification of a few hardware components planned for the first semester of 2018, the FEL-2 layout will be suitable for EEHG at wavelengths down to approximately 6 nm.  
MOP010 Constraints on Pulse Duration Produced by Echo-Enabled Harmonic Generation 1
  • G. Penn
    LBNL, Berkeley, California, USA
  • B.W. Garcia, E. Hemsing, G. Marcus
    SLAC, Menlo Park, California, USA
  Funding: This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract Nos. DE-AC02-05CH11231 and DE-AC02-76SF00515.
Echo-enabled harmonic generation (EEHG) is well-suited for producing long, coherent pulses at high harmonics of seeding lasers. There have also been schemes proposed to adapt EEHG to output extremely short, sub-fs pulses by beam manipulations or through extremely short seed lasers, but the photon flux is generally lower than that produced by other schemes. For the standard EEHG layout, it is still interesting to consider different parameter regimes and evaluate how short a pulse can be generated. EEHG at high harmonics uses a large dispersive chicane which can change the relative distance of electrons by substantial distances, even longer than a typical FEL coherence length. We evaluate the ability to produce short pulses (in the femtosecond to 10-fs range) using a combination of theory and simulations.
poster icon Poster MOP010 [0.446 MB]  
MOP017 Echo-Enabled Harmonic Generation Results with Energy Chirp 1
  • B.W. Garcia, M.P. Dunning, C. Hast, E. Hemsing, T.O. Raubenheimer, G. Stupakov
    SLAC, Menlo Park, California, USA
  • D. Xiang
    Shanghai Jiao Tong University, Shanghai, People's Republic of China
  We report here on several experimental results from the NLCTA at SLAC involving chirped Echo-Enabled Harmonic Generation (EEHG) beams. We directly observe the sensitivity of the different n EEHG modes to a linear beam chirp. This differential sensitivity results in a multi-color EEHG signal which can be fine tuned through the EEHG parameters and beam chirp. We also generate a beam which, due to a timing delay between the two seed lasers, contains both regions of EEHG and High-Gain Harmonic Generation (HGHG) bunching. The two regions are clearly separated on the resulting radiation spectrum due to a linear energy chirp, and one can simultaneously monitor their sensitivities.  
Generating Subfemtosecond Hard X-Ray Pulses with Optimized Nonlinear Bunch Compression  
  • S. Huang
    PKU, Beijing, People's Republic of China
  • Y. Ding, Y. Feng, E. Hemsing, Z. Huang, J. Krzywinski, A.A. Lutman, A. Marinelli, T.J. Maxwell, D. Zhu
    SLAC, Menlo Park, California, USA
  Funding: This work is supported by the U.S. Department of Energy Contract No. DE-AC02-76SF00515 and the National Key Research and Development Program of China (Grant No. 2016YFA0401904).
A simple method for generating single-spike hard x-ray pulses in free-electron lasers (FELs) has been developed at the Linac Coherent Light Source (LCLS). By optimizing the electron bunch compression in experiments, we have obtained half of the hard x-ray FEL shots containing single-spike spectrum. At 5.6-keV photon energy, the single-spike shots have a mean pulse energy of about 10 J with 70% intensity fluctuation and the pulse width (full width at half maximum) is evaluated to be at 200-attosecond level.
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.