Seeding and Seeded FELs
Paper Title Page
TUOA03
 Two Novel Laser-Based Seeding Schemes for X-ray FELs  
 
  • Q.R. Marksteiner, K. Bishofberger, B.E. Carlsten, L.D. Duffy, C.M. Fortgang, P.L. Walstrom, N.A. Yampolsky
    LANL, Los Alamos, New Mexico, USA
  
  Funding: We acknowledge the support of the LDRD program at Los Alamos National Laboratory.
The proposed Matter-Radiation Interactions in Extremes (MaRIE) hard X-ray facility at Los Alamos National Laboratory (LANL) has some user requirements that require longitudinal bandwidths that are an order of magnitude smaller than the bandwidths provided by a SASE FEL. We discuss two novel laser-based harmonic generation schemes for x-ray FELs which could be incorporated into x-ray FELs in order to achieve these bandwidths. The first scheme is a hybrid of Echo-Enabled Harmonic Generation (EEHG) and High-Gain Harmonic Generation (HGHG), which only requires a single laser with relatively low power, compared with EEHG. The second scheme uses a pair of Emittance Exchangers (EEX) after a laser modulator, in order to compress the modulation by a large factor. The strengths and design constraints of these schemes will be discussed, and a general formulism for studying the evolution of bandwidth and bunching factors in a complex seeding scheme will be presented [Yampolsky, arXiv:111.0553v1]. We will show how the hybrid EEHG-HGHG scheme can be incorporated into the NGLS for increased seeding performance. 		 
slides icon Slides TUOA03 [3.702 MB]  
 
TUOA04
 Coherence Properties of FERMI@Elettra  
 
  • B. Mahieu, E. Allaria, G. De Ninno, E. Ferrari, F. Parmigiani, L. Raimondi, S. Spampinati, C. Spezzani, C. Svetina, M. Zangrando
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • B. Mahieu
    CEA/DSM/DRECAM/SPAM, Gif-sur-Yvette, France
  
  We report the results of a campaign of measurements aimed at characterizing the spatial and temporal coherence of the FERMI@Elettra free-electron laser. The results (the first obtained on a high-gain seeded single-pass free-electron laser), are compared with those obtained on other (SASE-based) facilities.  
slides icon Slides TUOA04 [3.274 MB]  
 
TUOAI01 First Direct Seeding at 38nm 197
 
  • C. Lechner, A. Azima, J. Bödewadt, M. Drescher, E. Hass, U. Hipp, Th. Maltezopoulos, V. Miltchev, M. Rehders, J. Rönsch-Schulenburg, J. Roßbach, R. Tarkeshian, M. Wieland
    Uni HH, Hamburg, Germany
  • S. Ackermann, S. Bajt, H. Dachraoui, H. Delsim-Hashemi, S. Düsterer, B. Faatz, K. Honkavaara, T. Laarmann, M. Mittenzwey, H. Schlarb, S. Schreiber, L. Schroedter, M. Tischer
    DESY, Hamburg, Germany
  • F. Curbis
    MAX-lab, Lund, Sweden
  • R. Ischebeck
    PSI, Villigen PSI, Switzerland
  • S. Khan
    DELTA, Dortmund, Germany
  • V. Wacker
    University of Hamburg, Hamburg, Germany
  
  Funding: The project is supported by the Federal Ministry of Education and Research of Germany under contract No. 05 K10GU1 and by the German Research Foundation programme graduate school 1355.
The sFLASH project at DESY is an experiment to study direct seeding using a source based on the high-harmonic generation (HHG) process. In contrast to SASE, a seeded FEL exhibits greatly improved longitudinal coherence and higher shot-to-shot stability (both spectral and energetic). In addition, the output of the seeded FEL is intrinsically synchronized to the HHG drive laser, thus enabling pump-probe experiments with a resolution of the order of 10 fs. The installation and successful commissioning of the sFLASH components in 2010/2011 has been followed by a planned upgrade in autumn 2011. As a result of these improvements, in spring 2012 direct HHG seeding at 38 nm has been successfully demonstrated. In this contribution, we describe the experimental layout and announce the first seeding at 38 nm. 		 
slides icon Slides TUOAI01 [11.553 MB]  
 
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]  
 
TUOB04 Comparison of Hard X-Ray Self-seeding with SASE after a Monochromator at LCLS 217
 
  • J.J. Welch, F.-J. Decker, J.B. Hastings, Z. Huang, A.A. Lutman, M. Messerschmidt, J.L. Turner
    SLAC, Menlo Park, California, USA
  
  Funding: ** Work supported in part by the DOE Contract DE-AC02-76SF00515.
Self-seeding of a hard x-ray FEL was demonstrated at LCLS in January 2012 and produced a factor of 40-50 bandwidth reduction using a electron bunch charge of 20-40 pC*. For many hard x-ray users, the photon intensity after a monochromator is an important performance parameter. In this paper, we report results from a subsequent study of self-seeding performance using the Si (111) K-monochromator with a full bandwidth of 1.2 eV at 8.2 keV. These include a direct comparison of the average intensity of the monochromatized seeded beam with that of a monochromatized fully tuned-up SASE beam, in both cases using 150 pC bunch charge. The intensity distribution, fluctuations, and spatial profiles of the monochromatized radiation are studied and compared.
* J. Amann, et. al, Nature Photonics, to be published 		 
slides icon Slides TUOB04 [1.417 MB]  
 
TUPD08 Tolerances for a Seeded Free Electron Laser 241
 
  • J. Wu, T.O. Raubenheimer
    SLAC, Menlo Park, California, USA
  
  Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515.
Tolerance and stability are important issues for designing and operating accelerator and FEL. Jitter can come from various sources. We identify and study well known sources as well as some particular ones, important for a seeded tapered high power FEL. Seed laser phase error, electron bunch current profile, self-seeding residual density bunching and energy modulation after the chicane, undulator wakefield, and phase errors in the undulator breaks are just a few important examples. Schemes to improve the stability of a seeded FEL are also discussed. 		 
 
TUPD10 Status of Polarization Control Experiment at Shanghai Deep Ultraviolet Free Electron Laser 245
 
  • H.X. Deng, J.H. Chen, Z.M. Dai, Y. Fan, C. Feng, L. Feng, Y.Z. He, T. Lan, B. Liu, D. Wang, X.T. Wang, Z.S. Wang, J.D. Zhang, M. Zhang, M. Zhang, T. Zhang, Z.T. Zhao
    SINAP, Shanghai, People's Republic of China
  • L. Song
    BUAA, Beijing, People's Republic of China
  
  A polarization control experiment using a pair of crossed undulators has bee proposed for the Shanghai deep ultraviolet free electron laser (FEL) test facility. Numerical simulation indicates that, with the phase-shifter between the two crossed undulators, Fourier-Transform-Limited output radiation with 100nJ order pulse energy, 5ps full pulse length and circular polarization degree above 90% could be achieved. The physical design study and the experimental setup status are presented in the paper.  
 
TUPD11 Optimization of HHG Seeding at Flash II 249
 
  • S. Ackermann, B. Faatz
    DESY, Hamburg, Germany
  • V. Miltchev, J. Roßbach
    Uni HH, Hamburg, Germany
  
  FLASH* delivers coherent FEL radiation suitable for a variety of scientific purposes. In order to provide more beam time to the photon experiments, the FLASH II project, consisting of a second undulator branch and a new experimental Hall driven by the same superconducting modules as FLASH today has been started in 2008. While in the present undulator the kinetic energy of the electrons has to be changed in order to change the wavelength, the new beamline will benefit from variable gap undulators which will allow to have largely independent radiation wavelength; in the range of 10 to 40 nm an HHG seeding option is foreseen which will improve radiation quality for users beyond SASE. For experiments it is important to have the source point of the FEL radiation at the same position, close to the end of the undulator. However, one would like to keep the HHG focus at a fixed longitudinal position, such that wavelength changes will not require adjustments of the HHG focus. In this contribution, we will present the optimization of these conflicting requirements by opening undulator gaps at wavelength dependent positions, keeping both the seeding point and the source point for users fixed.
* The Free-Electron Laser in Hamburg 		 
 
TUPD12 Extension of Self-seeding to Hard X-rays > 10 keV as a Way to Increase User Access at the European XFEL 253
 
  • G. Geloni
    XFEL. EU, Hamburg, Germany
  • V. Kocharyan, E. Saldin
    DESY, Hamburg, Germany
  
  We propose to use a self-seeding scheme with single crystal monochromator at the European X-ray FEL to produce monochromatic, high-power radiation at 16 keV. The FEL power of the transform-limited pulses can reach about 100 GW by exploiting tapering in the tunable-gap baseline undulator. The combination of high photon energy, high peak power, and very narrow bandwidth opens a new range of applications, and allows to increase the user capacity and exploit the high repetition rate of the European XFEL. Dealing with monochromatic hard X-ray radiation one may use crystals as deflectors with minimum beam loss. To this end, a photon beam distribution system based on the use of crystals in the Bragg reflection geometry is proposed for future study and possible extension of the baseline facility. They can be repeated a number of times to form an almost complete (one meter scale) ring with an angle of 20 degrees between two neighboring lines. The reflectivity of crystal deflectors can be switched fast enough by flipping the crystals with piezo-electric devices. It is then possible to distribute monochromatic hard X-rays among 10 independent instruments.  
 
TUPD13 Progress Towards HGHG and EEHG at FLASH 257
 
  • K.E. Hacker, C. Behrens, H. Schlarb
    DESY, Hamburg, Germany
  • G. Angelova Hamberg, V.G. Ziemann
    Uppsala University, Uppsala, Sweden
  • A. Azima, J. Bödewadt
    Uni HH, Hamburg, Germany
  • S. Khan, R. Molo
    DELTA, Dortmund, Germany
  • P. Salén, P. van der Meulen
    FYSIKUM, AlbaNova, Stockholm University, Stockholm, Sweden
  
  Funding: BMBF 05K10PE1 and DESY
New infrastructure was built at FLASH to enable 30-100 fs long, milliJoule pulses of 270 nm light to seed the electron beam with HGHG and EEHG techniques, targeting wavelengths in the range from 10 nm to 40 nm. HGHG, or High Gain Harmonic Generation, and EEHG, or Echo-Enabled Harmonic Generation, utilize an external laser together with chicanes and undulators in order to generate a bunched beam which will radiate in a subsequent undulator. In the case of HGHG, the beam is bunched at the seed laser wavelength, radiating harmonics thereof in the radiator. In the case of EEHG, the beam is bunched at a harmonic of the seed wavelength, radiating that same harmonic in the radiator. The properties of the setup, commissioning difficulties and the inital attempts at HGHG seeding at 38.5 nm will be described. 		 
 
TUPD14 Optical Replica Synthesizer to be Recommissioned with 270 nm Seed at FLASH 261
 
  • K.E. Hacker
    DESY, Hamburg, Germany
  • G. Angelova Hamberg, V.G. Ziemann
    Uppsala University, Uppsala, Sweden
  • S. Khan, R. Molo
    DELTA, Dortmund, Germany
  • P. Salén, P. van der Meulen
    FYSIKUM, AlbaNova, Stockholm University, Stockholm, Sweden
  
  Funding: BMBF 05K010PE1, grant 621-2009-2926 and DESY
The Optical Replica Synthesizer at FLASH was first commissioned in 2008 with an 800 nm seed. This wavelength proved to be problematic due to the fact that the COTR resulting from a microbunching instability at that wavelength was often as strong or stronger than the radiation from the seeded and bunched beam. It has since been observed that the microbunches which are responsible for the unwanted COTR can be smeared out in the dogleg if they are shorter than 600 nm. This opens the possibility to try the same experiment with a shorter wavelength and avoid the problems with the unwanted background signal from the microbunching instability. This is the motivation behind a new experimental design involving a new 270 nm seed laser and a new pulse length detection device to replace the old 800 nm seed and pulse length detection device. Details about the experiment design and commissioning plans will be described. 		 
 
TUPD15 Seeded Coherent Harmonic Generation with in-line Gas Target 265
 
  • F. Curbis, N. Čutić, O. Karlberg, F. Lindau, E. Mansten, S. Thorin, S. Werin
    MAX-lab, Lund, Sweden
  • F. Brizuela, B. Kim, D. Kroon, A. L'Huillier
    Lund University, Division of Atomic Physics, Lund, Sweden
  • M. Gisselbrecht
    SLF, Lund, Sweden
  
  The test-FEL at MAX-lab already demonstrated seeded coherent harmonic generation down to 40 nm*. As next step in the development of seeding techniques we plan to use a gas target to generate harmonics of the drive laser and seed the electron beam with them. In order to optimize the injection process, our aim is to place the gas target for harmonic generation as close as possible to the first undulator. In order to minimize the losses the transport of the drive laser is done with a minimal number of mirrors and there are neither focusing nor filtering elements between the harmonic chamber and the first undulator. This will be the first experiment that will imprint energy modulation to the electron beam by harmonics generated in gas. The wavelength range of the harmonics that will be used as seed is around 100 nm and we plan to detect the coherent harmonic signal of the second harmonic generated in the radiator. The flexibility of the set-up will allow to drive the HG process with the fundamental wavelength or the second harmonic or the combination of them. Adding the second harmonic will lead to the generation of even harmonics, thus increasing the range of seeding wavelength.
N. Cutic, et al., "Vacuum ultraviolet circularly polarized coherent femtosecond pulses from laser seeded relativistic electrons", Phys. Rev. Spec. Top. Accel. Beams 14, 030706 (2011)
 		 
 
TUPD17 Seeding of SPARC-FEL with a Tunable Fibre-based Source 269
 
  • N.Y. Joly
    University of Erlangen-Nuremberg, Erlangen-Nuremberg, Germany
  • S. Bielawski
    PhLAM/CERCLA, Villeneuve d'Ascq Cedex, France
  • W. Chang, P. Hölzer, K. Mak, P.St.J. Russell, F. Tani, J.C. Travers
    Max Planck Institute for the Science of Light, Erlangen, Germany
  • F. Ciocci, L. Giannessi, A. Petralia, M. Quattromini
    ENEA C.R. Frascati, Frascati (Roma), Italy
  • M.-E. Couprie, M. Labat, T. Tanikawa
    SOLEIL, Gif-sur-Yvette, France
  • G. De Ninno, B. Mahieu
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • G. Gatti
    INFN/LNF, Frascati (Roma), Italy
  • V. Petrillo
    Istituto Nazionale di Fisica Nucleare, Milano, Italy
  • J.V. Rau
    ISM-CNR, Rome, Italy
  
  Instead of seeding a free electron laser in the UV-VUV with a frequency doubled or tripled laser or high order harmonics, here we investigate and present the first results on seeding SPARC-FEL with a fiber-based tunable ultraviolet source. The seed generation system consists of a kagomé hollow-core photonic crystal fiber filled with noble gas. Diffraction-limited DUV pulses of >50 nJ and fs-duration which are continuously tunable from below 200 nm to above 300 nm are generated. The process is based on soliton-effect self-compression of the pump pulse down to a few optical cycles, accompanied by the emission of a resonant dispersive wave in the DUV spectral region. The quality of the compression highly depends on the pump pulse duration, and ideally, pulses <60 fs should be used. Our experimental set-up and associated GENESIS simulations enable us to study the utility of the seed tunability, and the influence of the seed quality, on the performance of the SPARC-FEL in the 200-300 nm range.  
 
TUPD19 The Radiator-first HGHG Multi-MHz X-ray FEL Concept 273
 
  • M.W. Reinsch, G. Penn
    LBNL, Berkeley, California, USA
  • P.R. Gandhi, J.S. Wurtele
    UCB, Berkeley, California, USA
  
  A novel configuration for a high repetition rate X-ray FEL is investigated. In this scheme longitudinally coherent FEL pulses are obtained using a high gain harmonic generation (HGHG) system in which the seed power is generated in an FEL oscillator downstream of the HGHG section. The oscillator is powered by the spent beams that leave the HGHG radiator. Radiation from the oscillator is sent to the modulator of the HGHG section. The dynamics and stability of the radiator-first scheme is explored analytically and numerically. A single-pass map is derived using a semi-analytic model for FEL gain and saturation. Iteration of the map is shown to be in good agreement with simulations. A numerical example is presented for a soft X-ray FEL in which the oscillator operates at 13.4 nm and HGHG radiation is generated at 1.34 nm. This radiator-first configuration potentially solves (i) the challenge of finding sources to seed future FELs driven by multi-MHz superconducting RF linacs and (ii) the difficulty of producing X-ray radiation with a bunch that exits an oscillator in the more "natural" configuration in which the oscillator precedes the radiator.  
 
TUPD20 Soft X-ray SASE and Self-seeding Studies for a Next-generation Light Source 277
 
  • G. Penn, P. Emma, D. Prosnitz, J. Qiang, M.W. Reinsch
    LBNL, Berkeley, California, USA
  
  Funding: This work was supported by the Director, Office of Science, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
In the self-seeding scheme, the longitudinal coherence and spectral density of an unseeded FEL can be improved [*] by placing a monochromator at a location before the radiation reaches saturation levels, followed by a second stage of amplification. The final output pulse properties are determined by a complex combination of the monochromator properties, undulator settings, variations in the electron beam, and wakefields. We perform simulations for the output of SASE and self-seeded configurations for a soft x-ray FEL using both idealized beams and realistic beams from start-to-end simulations. These studies include cross-planar undulators dedicated to polarization control [**].
[*] J. Feldhaus, E.L. Saldin, J.R. Schneider, E.A. Schneidmiller, and
M.V. Yurkov, Optics Commun. 140 (1997) 341-352.
[**] K.-J. Kim, Nucl. Instrum. Methods A 445 (2000) 329-332.
 		 
 
TUPD21 Self-Seeding Design for SwissFEL 281
 
  • E. Prat, S. Reiche
    PSI, Villigen PSI, Switzerland
  • D.J. Dunning
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  
  The SwissFEL facility, planned at the Paul Scherrer Institute, is based on the SASE operation of a hard (1-7 Å) and soft (7-70 Å) X-ray FEL beamline. In addition, seeding is foreseen for the soft X-ray beamline (down to a wavelength of 10 Å), and it is currently also under consideration for the hard X-ray beamline. We have investigated two methods, Echo-Enabled Harmonic Generation (EEHG) and self-seeding for each of the two FEL beamlines. Presently we consider self-seeding the most robust and lowest risk strategy for both lines. The paper discusses our considerations and presents the design of self-seeding implementation for the soft and the hard X-ray beamlines including the layout and simulation results.  
 
TUPD22 Generating Multiple Superradiance Pulses in a Slippage-dominant Free-electron Laser Amplifier 285
 
  • X. Yang, Y. Shen
    BNL, Upton, Long Island, New York, USA
  
  We report the first numerical demonstration of the generation of multiple superradiance pulses in a slippage-dominant free-electron laser amplifier. In this simulation, the 1st and 2nd multiple radiation-pulses are created from the deformation of the longitudinal phase space. Our simulation confirmed controllability over the temporal profile of these pulses, and paves the way for applying this technique, such as generating multiple pulses for slippage-dominant laser-seeded FELs.