TUPB  —  Poster: Seeding and Seeded FELs   (24-Aug-10   13:33—15:00)

Paper Title Page
TUPB02 A Simple Method for Controlling the Line Width of SASE X-Ray FELs 258
 
  • G. Geloni
    European XFEL GmbH, Hamburg
  • V. Kocharyan, E. Saldin
    DESY, Hamburg
 
 

We describe a novel single-bunch self-seeding scheme to obtain highly monochromatic X-rays from a baseline XFEL undulator. For a single-bunch self-seeding scheme a long electron beam bypass is required, implying modifications of the baseline undulator configuration. We avoid such requirement exploiting a single crystal in the transmission direction. The method can be realized using a temporal windowing technique, requiring a magnetic delay for the electron bunch only. The proposed setup is extremely simple and composed of as few as two simple elements: the crystal and the short magnetic chicane, which accomplishes three tasks by itself. It creates an offset for crystal installation, removes the electron micro-bunching from the first undulator, and acts as a delay line for temporal windowing. Using a single crystal installed within a short magnetic chicane in the baseline undulator, it is possible to decrease the bandwidth of the radiation well beyond the XFEL design down to 10-5. The installation of the magnetic chicane does not perturb the undulator focusing system and does not interfere with the baseline mode of operation.

 
TUPB04 High Harmonic Source for Seeding of FERMI@Elettra 262
 
  • P.J.M. van der Slot, H.M.J. Bastiaens, K.-J. Boller, S.J. Goh
    Mesa+, Enschede
  • S. Biedron, M.B. Danailov, S.V. Milton
    ELETTRA, Basovizza
  • J.L. Herek
    UT-MESA+ OS, Enschede
 
 

FERMI@Elettra is a free electron laser user facility currently under construction at Sincrotrone Trieste S.C.p.A. Its goals are to produce high-brightness, ultra-short pulses with wavelengths ranging from 100 - 20 nm (FEL1) and 40 - 4 nm (FEL2) and deliver these pulses to a wide range of user experiments. Currently, FERMI uses the HGHG technique to improve both the stability and the longitudinal and spectral coherence of the output of the laser. Direct seeding of FEL1 using a High Harmonic (HH) source is also foreseen and allows a direct comparison between the two seeding methods. For an HH source, we will use neutral atoms in a hollow waveguide in combination with coherent control of the drive laser pulse to provide wavelength tuning as well as selective enhancement of the harmonic orders. For direct seeding of FEL 2 we propose HH generation from ions in a modulated plasma waveguide. The ions allow generation of shorter wavelengths, while the modulated plasma waveguide provides a long interaction length as well as quasi-phase matching for boosting the output energy of the source. In this paper, we will present the HH source for FEL1 as well as a concept for HH seeding of FEL2.

 
TUPB08 Staged Self-Seeding Scheme for Narrow Bandwidth, Ultra-Short X-ray Harmonic Generation Free Electron Laser at LINAC Coherent Light Source 266
 
  • J. Wu, P. Emma, J.B. Hastings
    SLAC, Menlo Park, California
  • C. Pellegrini
    UCLA, Los Angeles, California
 
 

Success of the world's first x-ray (0.15-1.5 nm) free electron laser (FEL) - LCLS - at SLAC opens the gate for new science. In this paper, we study the FEL performance for a two-stage self-seeding scheme by introducing a photon monochromator and an electron by-pass in the undulator system. The FEL generated in the first part of the undulator system is purified in spectrum, recombines with the electron bunch, and is amplified in the second part of the undulator system to saturation. Such modifications will improve the FEL longitudinal coherence, reducing the FEL band-width by two-orders of magnitude, but with similar peak power; hence improving the peak brightness by two-orders of magnitude. Such a self-seeding scheme is studied for both soft x-ray (200 eV to 2 keV) and hard x-ray (800 eV to 8 keV) cases with single electron bunch. The photon monochromator system is configurated as variable line spacing gratings for soft x-ray and single crystal for hard x-ray. Harmonic Generation and Chirped FEL are also considered aiming at reaching even shorter wavelength x-ray photons and at generating FEL pulse with even shorter temporal duration, respectively.

 
TUPB10 Optics for Self-Seeding Soft X-ray FEL Undulators 270
 
  • Y. Feng, J.B. Hastings, J. Krzywinski, M. Rowen, J. Wu
    SLAC, Menlo Park, California
  • P.A. Heimann
    LBNL, Berkeley, California
 
 

A complete optical system including grating monochromator and mirrors was designed to provide self-seeding of the soft X-ray undulators to be possibly built as part of the LCLS-II project. The grating monochromator consisted of a cylindrical horizontally focusing mirror, a plane vertically deflecting pre-mirror, a variable-line-spacing plane vertically deflecting grating, a horizontal exit slits, and a spherical vertically collimating mirror. The grating monochromator was designed to operate in the fixed-focus mode and tuning of the energy was designed to be achieved by rotations of only the pre-mirror and the grating. Only one ruling of 2200 l/mm was needed to cover the energy range from 200 to 2000 eV with an almost constant resolving power of greater than 22700. The monochromator would produce fully transform-limited pulses of 12 fs (rms) long at 2000 eV or 120 fs (rms) long at 200 eV with sufficient power to allow seeding. The optical system produced a slightly energy-dependent time delay of about 10 ps. The transverse size of the input beam was preserved in the horizontal direction, but was reduced in the vertical direction depending on the tuning energy.

 
TUPB11 Noise Amplification in HGHG Seeding 274
 
  • G.V. Stupakov
    SLAC, Menlo Park, California
 
 

It is well known that harmonic generation in HGHG amplifies the shot noise in the beam. In this work, we introduce a framework for theoretical description of the noise dynamics in such a device consisting from un undulator-modulator and a chicane. We propose to consider the interaction of particles in the modulator-undulator through the radiation field as a source which modifies the noise level in the beam. The coherent part of this interaction is responsible for the FEL process while the random part introduces correlations in the particle's positions and modifies the noise properties of the beam. We develop a 1D version of the method and apply it to the HGHG seeding mechanism.

 
TUPB12 Noise Amplification in Echo-Enabled Harmonic Generation (EEHG) 278
 
  • G.V. Stupakov, Z. Huang, D.F. Ratner
    SLAC, Menlo Park, California
 
 

It is generally accepted that harmonic-generation seeding in FELs amplifies the noise in the beam and enhances the spontaneous component of the FEL radiation. In this paper we analyze the noise dynamics caused by particle interaction in the undulators of the EEHG seeding mechanism. We develop a 1D model of the noise evolution through the system and calculate the amplification factor as a function of frequency. Our results are applied to a typical soft x-ray EEHG FEL.

 
TUPB13 Echo-Seeding Options for LCLS-II 282
 
  • D. Xiang, G.V. Stupakov
    SLAC, Menlo Park, California
 
 

The success of LCLS has opened up a new era of x-ray sciences. An upgrade to LCLS is currently being planned to enhance its capabilities. In this paper we study the feasibility of using the echo-enabled harmonic generation (EEHG) technique to generate narrow bandwidth soft x-ray radiation in the proposed LCLS-II soft x-ray beam line. We focus on the conceptual design, the technical implementation and the expected performances of the echo-seeding scheme. We will also show how the echo-seeding scheme allows one to generate two color x-ray pulses with the higher energy photons leading the lower energy ones as is favored by the x-ray pump-probe experiments.

 
TUPB16 Numerical Study on Coherent Harmonic Generation Free Electron Laser Seeded by Chirped External Laser 286
 
  • H. Zen, M. Adachi, M. Katoh
    UVSOR, Okazaki
  • M. Hosaka, Y. Taira, N. Yamamoto
    Nagoya University, Nagoya
  • T. Tanikawa
    Sokendai - Okazaki, Okazaki, Aichi
 
 

Coherent Harmonic Generation Free Electron Laser (CHG-FEL)* ** is a short pulse and coherent radiation source in vacuum ultra-violet regime. A measurement of CHG-FEL spectrum*** has been done and sidebands in spectrum were observed under an over-bunching condition. The measurement was done with chirped seed laser to avoid strong over-bunching of electron beam and to obtain larger pulse energy for high signal to noise ratio. In the paper ***, however, the seed laser chirping was not taken into account in the numerical analysis and the numerical results qualitatively agreed with experimental results but quantitatively not. We consider that the discrepancy was caused by the chirping property of the seed laser, and thus we have developed a time dependent simulation code which can deal the effect of seed laser chirping. Results of the code qualitatively agreed well with the shape of measured spectrum, not only bandwidth but also the sideband structure. And the code was used to evaluate the temporal and spectral property of CHG-FEL seeded by a chirped laser. The code revealed the spectral widening and chirped property of CHG-FEL pulse when the CHG-FEL is driven by a chirped seed laser.


* L. H. Yu et al., Phys. Rev. A 44, 5178 (1991).
** G. D. Ninno et al., Phys. Rev. Lett. {10}1, 053902 (2008).
***M. Labat et al., Phys. Rev. Lett. {10}2, 014801 (2009).

 
TUPB17 Generation of Atto-Second Water Window Coherent X-Ray Radiation Through Modulation Compression 290
 
  • J. Qiang
    LBNL, Berkeley, California
  • J. Wu
    SLAC, Menlo Park, California
 
 

In this paper, we propose a scheme to generate atto-second to femto-second tunable water window (~2-4 nm) coherent X-ray radiation for future light source applications. This scheme improves the previously proposed modulation compression method [1] by using a 10 pC, 100 μm electron beam at 2 GeV energy, a 200 nm seeding laser, an X-band linac, two opposite sign bunch compressors, and a long wavelength laser to generate a prebunched, kilo-Amper current beam with a modulation wavelength within the water window. Such a beam will be sent into an undulator to generate a short pulse transverse and temporal coherent soft X-ray radiation. The requirement of initial seeding laser power is small. The electron beam at the entrance of undulator can have sub micron normalized emittance.


[1] J. Qiang, "Short wavelength seeding through compression for free electron lasers," NIM-A,10.{10}16/j.nima.2010.04.053, 2010.

 
TUPB18 FEL Experiments at SPARC 294
 
  • L. Giannessi, F. Ciocci, G. Dattoli, M. Del Franco, A. Petralia, M. Quattromini, C. Ronsivalle, E. Sabia, I.P. Spassovsky, V. Surrenti
    ENEA C.R. Frascati, Frascati (Roma)
  • D. Alesini, M. Bellaveglia, M. Castellano, E. Chiadroni, L. Cultrera, G. Di Pirro, M. Ferrario, L. Ficcadenti, D. Filippetto, A. Gallo, G. Gatti, E. Pace, B. Spataro, C. Vaccarezza, C. Vicario
    INFN/LNF, Frascati (Roma)
  • A. Bacci, V. Petrillo, A.R. Rossi, L. Serafini
    Istituto Nazionale di Fisica Nucleare, Milano
  • M. Bougeard, B. Carré
    CEA, Gif-sur-Yvette
  • F. Briquez, M.-E. Couprie, M. Labat
    SOLEIL, Gif-sur-Yvette
  • A. Cianchi
    Università di Roma II Tor Vergata, Roma
  • F. Frassetto, L. P. Poletto
    LUXOR, Padova
  • G. Lambert
    LOA, Palaiseau
  • G. Marcus, J.B. Rosenzweig
    UCLA, Los Angeles, California
  • M. Moreno, M. Serluca
    INFN-Roma, Roma
  • A. Mostacci
    Rome University La Sapienza, Roma
  • J.V. Rau, V. Rossi Albertini
    ISM-CNR, Rome
 
 

SPARC is a single pass free electron laser test facility realized in collaboration between the main Italian research institutions and devoted to experiments of light amplification in different beam conditions. While the laser was commissioned in self amplified spontaneous emission (SASE) mode during the last year, the operation in seeded mode has been recently demonstrated. The amplifier has been seeded with the second harmonic of the Ti:Sa driver laser generated in a crystal and with higher order VUV harmonics generated in a gas cell. The comparison between seeded and unseeded FEL emission will be discussed. The laser has been also operated in a new SASE configuration with a strongly chirped longitudinal e-beam phase space resulting from the RF compression. The chirp has been compensated by accordingly tapering the undulator gaps. Spectra with and without taper have been collected. An increase of about a factor 5 of the pulse energy in combination with spectra with a single longitudinal coherence region have been detected in presence of the taper. The combination of the chirp with the input seed is under study.

 
TUPB21 Characterization of Seeded FEL Pulses at FLASH: Status, Challenges and Opportunities 298
 
  • F. Curbis, A. Azima, J. Bödewadt, H. Delsim-Hashemi, M. Drescher, U. Hipp, Th. Maltezopoulos, V. Miltchev, M. Mittenzwey, M. Rehders, J. Roßbach, J. Rönsch-Schulenburg, R. Tarkeshian, M. Wieland
    Uni HH, Hamburg
  • S. Bajt, S. Düsterer, T. Laarmann, H. Schlarb
    DESY, Hamburg
 
 

Since 2004, the free-electron laser FLASH at DESY has operated in the Self-Amplified Stimulated Emission mode (SASE), delivering gigawatt pulses with wavelengths between 6.5 nm and 40 nm in the femtosecond domain. In 2009, DESY installed an additional radiofrequency module for controlling the phase space of the electron bunches that gives the possibility to generate bunches with high peak currents (~kA), but ten times larger pulse durations (~250 fs) compared to the previous configuration. The relaxed timing requirements of the new configuration make it possible to externally seed FLASH with high-order harmonics of an optical laser below 40nm generated in a gas target (sFLASH). Because in this case amplification is triggered within the seed pulse length instead of starting from shot-noise as in the SASE process, spikes in the temporal/spectral pulse profiles should be absent and the temporal jitter should be eliminated. In this contribution the present status of the sFLASH photon diagnostics including first commissioning will be discussed.

 
TUPB23 Experimental Demonstration of Wideband Tunability of an Ultrafast Laser-Seeded Free-Electron Laser 302
 
  • X. Yang, Y. Hidaka, J.B. Murphy, B. Podobedov, S. Seletskiy, Y. Shen, X.J. Wang
    BNL, Upton, Long Island, New York
 
 

We report the first experimental characterization of the wideband tunability of an ultrafast laser seeded FEL using a short seed laser pulse (140 fs in FWHM) and a variable energy electron beam. The experiments were conducted at the NSLS SDL and the FEL output spectrum and pulse energy were measured versus the electron beam energy. A significant spectral tuning range (8%) was observed. The experiment is in good agreement with predictions using the Perseo simulation code.

 
TUPB25 Saturation Phenomena of VUV Coherent Harmonic Generation at UVSOR-II 306
 
  • T. Tanikawa
    Sokendai - Okazaki, Okazaki, Aichi
  • M. Adachi, M. Katoh, J. Yamazaki, H. Zen
    UVSOR, Okazaki
  • M. Hosaka, Y. Taira, N. Yamamoto
    Nagoya University, Nagoya
 
 

Light source technologies based on laser seeding are under development at the UVSOR-II electron storage ring. In the last FEL conference (FEL2009), we reported spectral measurements of coherent harmonic generation (CHG) seeded by the fundamental of Ti: Sapphire laser, in the region of vacuum-ultra violet (VUV). In this conference, we will report some systematic measurements such as the undulator gap dependence and seed laser power dependence. In the laser power dependence, we have observed a saturation of CHG intensity. The result will be compared with simulations. A seeding light source based on high harmonic generation (HHG) in rare gas is under development. The status will be reported.

 
TUPB26 Past and Future of the DELTA Free-Electron Laser 310
 
  • H. Huck, R. Burek, S. Khan, A. Schick, G. Schmidt, K. Wille
    DELTA, Dortmund
 
 

The storage-ring FEL at DELTA has been successfully operated with different filling patterns and temporal structures following the installation of new mirror chambers three years ago. The modulation depth of the optical-klystron spectrum was used to measure the electron energy spread. The measured FEL output power at high beam currents strongly exceeded the predictions of the low-gain model. This could be explained by the microwave instability being damped significantly by the onset of the FEL interaction. In the near future, the optical klystron will be seeded by external ultrashort laser pulses in order to produce highly coherent, intense and ultrashort VUV pulses by coherent harmonic generation (CHG). Additionally, coherent ultrashort THz pulses will be generated several meters downstream of the optical klystron by the laser-induced gap in the electron bunch.