Author: Ding, Y.T.
Paper Title Page
TUOAI02
 Hard X-ray Self-Seeding at the LCLS  
 
  • R.R. Lindberg, W. Berg, D. Shu, Yu. Shvyd'ko, S. Stoupin, E. Trakhtenberg, A. Zholents
    ANL, Argonne, USA
  • J.W. Amann, F.-J. Decker, Y.T. Ding, Y. Feng, J.C. Frisch, D. Fritz, J.B. Hastings, Z. Huang, J. Krzywinski, H. Loos, A.A. Lutman, H.-D. Nuhn, D.F. Ratner, J.A. Rzepiela, D.R. Walz, J.J. Welch, J. Wu, D. Zhu
    SLAC, Menlo Park, California, USA
  • V.D. Blank, S. Terentiev
    TISNCM, Troitsk, Russia
  • P. Emma
    LBNL, Berkeley, California, USA
  • S. Spampinati
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  
  Funding: U.S. Dept. of Energy Office of Sciences under Contract No. DE-AC02-06CH11357
The Linac Coherent Light Source (LCLS) has produced extremely bright hard x-ray pulses using self-amplified spontaneous emission (SASE) since 2009. In SASE, the electron beam shot noise initiates the FEL gain, resulting in output radiation characterized by poor temporal coherence and a fluctuating spectrum whose normalized width is given by the FEL bandwidth. Recently, colleagues at DESY suggested a self-seeding scheme for the LCLS to reduce the bandwidth*. Here, the SASE produced in the first half of the undulator line is put through a simple diamond-based monochromator; the resulting monochromatic light trailing the main SASE pulse is used to seed the FEL interaction in the downstream undulators. We report on the experimental results implementing such a scheme at the LCLS, in which we have measured a reduction in bandwidth by a factor of 40-50 from that of SASE at 8-9 keV. The self-seeded FEL operates close to saturation, with the maximum output energy approximately equal to that with no seeding for low charge. The observed level of power fluctuations in the seeded output is presently rather large, and future plans focus on discovering their origins and reducing their magnitude.
* Geloni, V. Kocharyan ,and E.L. Saldin, DESY 10-133, arXiv:1008.3036 (2010)
 		 
slides icon Slides TUOAI02 [22.104 MB]  
 
TUOB03
 Complete Ultrafast X-ray Pulse Characterization at FELs  
 
  • A.L. Cavalieri, H. Bromberger, I. Grguras, S. Huber
    CFEL, Hamburg, Germany
  • C. Behrens, S. Düsterer, H. Schlarb
    DESY, Hamburg, Germany
  • C. Bostedt, J.D. Bozek, R.N. Coffee, Y.T. Ding, J.B. Hastings, M.C. Hoffmann, S. Schorb
    SLAC, Menlo Park, California, USA
  • J.T. Costello
    DCU, Dublin, Republic of Ireland
  • L.F. DiMauro
    Ohio State University, USA
  • G. Doumy
    ANL, Argonne, USA
  • W. Helml, R. Kienberger, A.R. Maier, W. Schweinberger
    MPQ, Garching, Munich, Germany
  • N.M. Kabachnik, T. Mazza, M. Meyer, T. Tschentscher
    XFEL. EU, Hamburg, Germany
  • A.K. Kazansky
    UPV-EHU, Leioa, Spain
  
  The ability to fully characterize X-ray pulses from free electron-lasers will underpin their exploitation in experiments ranging from single-molecule imaging to extreme timescale X-ray science. This issue is especially acute when confronted with the characteristics of current generation FELs operating on the principle of SASE, as most parameters fluctuate strongly from pulse to pulse. Here, we have extended the techniques of attosecond metrology with the use of single-cycle terahertz (THz) pulses, allowing for simultaneous, in-line, single-shot measurement of both the arrival time and temporal profile of FEL pulses on an absolute scale. The technique is non-invasive and could be incorporated in pump-probe experiments, eventually leading to characterization before and after interaction with most sample environments. Optical-laser-driven THz streaking measurements, revealing X-ray pulse structure shorter than 50 fs FWHM in the soft X-ray regime at FLASH and in the ~ keV range at LCLS will be discussed. With clear potential for improvement in resolution to the sub-10 fs regime, this method will ultimately allow for characterization of the shortest predicted few-femtosecond FEL pulses.  
slides icon Slides TUOB03 [15.857 MB]  
 
THOB02
 Transverse Gradient Undulator to Enhance the FEL Performance for a Laser-plasma Accelerator  
 
  • Z. Huang, Y.T. Ding
    SLAC, Menlo Park, California, USA
  • C.B. Schroeder
    LBNL, Berkeley, California, USA
  
  Compact laser-plasma accelerators can produce high energy electron beams with low emittance, high peak current but a rather large energy spread. The large energy spread hinders the potential applications for coherent FEL radiation generation. In this paper, we discuss a method to compensate the effects of beam energy spread by introducing a transverse field variation into the FEL undulator. Such a transverse gradient undulator together with a properly dispersed beam can greatly reduce the effects of electron energy spread and jitters on FEL performance. We present theoretical analysis and numerical simulations for SASE and seeded XUV and soft x-ray FELs based on laser plasma accelerators.  
slides icon Slides THOB02 [2.720 MB]  
 
THOC04
 Femtosecond X-ray Pulse Duration and Separation Measurement using a Cross-Correlation Technique  
 
  • Y.T. Ding, F.-J. Decker, Z. Huang, H. Loos, J.J. Welch, J. Wu, F. Zhou
    SLAC, Menlo Park, California, USA
  • P. Emma
    LBNL, Berkeley, California, USA
  • C. Feng
    SINAP, Shanghai, People's Republic of China
  
  At the Linac Coherent Light Source (LCLS), the emittance-spoiling foil is a very simple and effective method to control the output x-ray pulse duration [*]. In addition, double slotted foil can be used to generate two femotsecond x-ray pulses with variable time delays. In this paper, we report the first measurement of x-ray pulse duration and double x-ray pulse separation by using a cross-correlation technique between x-rays and electrons [**]. The measured pulse separation can be used to calibrate the foil setup, and pulse duration of less than 3 fs rms has been achieved. This technique can be used to provide critical temporal diagnostics for x-ray experiments that employ the emittance-spoiling foil.
[*] P. Emma et al., PRL 92, 074801 (2004).
[**] G. Geloni et al., DESY 10-008. 		 
slides icon Slides THOC04 [0.684 MB]  
 
THPD31 Sub-femtosecond Hard X-Ray Pulse from Very Low Charge Beam at LCLS 606
 
  • V. Wacker
    DESY, Hamburg, Germany
  • Y.T. Ding, J.C. Frisch, Z. Huang, C. Pellegrini, F. Zhou
    SLAC, Menlo Park, California, USA
  
  The Linac Coherent Light Source (LCLS) is an x-ray free-electron laser (FEL) at SLAC National Accelerator Laboratory, supporting a wide range of scientific research with an x-ray pulse length varying from a few to several hundred femtoseconds. There is also a large interest in even shorter, single-spike x-ray pulses, which will allow the investigation of matter at the atomic length (Å) and time scale (fs). In this paper, we investigate the FEL performance using 1pC and 3pC electron bunches at LCLS, based on the start-to-end simulations. With an optimization of the machine setup, simulations show that single spike, sub-femtosecond, hard x-ray pulses are achievable at this low charge.  
 
THPD56 Two-color FEL Generation based on Emittance-spoiler Technique 654
 
  • C. Feng, Y.T. Ding, Z. Huang, J. Krzywinski, A.A. Lutman
    SLAC, Menlo Park, California, USA
  
  Generation of two-pulse two-color x-ray radiation is attracting much attention within the free-electron laser (FEL) user community. Femtosecond x-ray pulses with variable durations and separation can be simply generated by the emittance-spoiler foil method* at the Linac Coherent Light Source (LCLS). In this paper, we describe three FEL schemes rely on the emittance-spoiler technique for the generation of two intense x-ray pulses with different colors. With a representative realistic set of parameters of LCLS, numerical simulations confirm that two femtosecond x-ray pulses at ten gigawatt level with different wavelengths around 1.8 nm can be generated by these schemes. The central wavelengths of the output pulses can be easily altered by changing strengths of the undulators.
*P. Emma et al., PRL 92, 074801 (2004). 		 
 
THPD57 Application of laser-plasma accelerator beams to Free-Electron Lasers 658
 
  • C.B. Schroeder, C. Benedetti, E. Esarey, W. Leemans, J. van Tilborg
    LBNL, Berkeley, California, USA
  • Y.T. Ding, Z. Huang
    SLAC, Menlo Park, California, USA
  • F. Grüner, A.R. Maier
    Uni HH, Hamburg, Germany
  
  Funding: This work was supported by the Director, Office of Science, of the U.S. Department of Energy under Contract No.DE-AC02-05CH11231.
Plasma waves excited by high-intensity, short-pulse lasers are able to generate hundreds of GV/m accelerating fields, enabling extremely compact accelerators for applications such as radiation generation. Laser-plasma accelerators (LPAs) produce ultrashort (femtosecond), 0.1-1 GeV electron bunches with high-peak (kA) currents and low (sub-micron) normalized transverse emittance, with 6D beam brightness comparable to state-of-the-art RF linac-based sources. FEL applications are presently limited by the longitudinal phase space distribution of the LPA beam. Beam phase space manipulation is considered to enable the application of LPA beams to FELs. LPA beam decompression (such that the energy spread over a coherence length is less than the FEL parameter) is examined as a path toward realizing an LPA-driven VUV FEL. The possibility of using a flat beam, with an energy correlation with transverse position, in a transverse gradient undulator is also explored. Laser-based FEL seeding options for improved coherence are considered.