Presentations with files available.

MOAIS03 R&D Experiments at BNL to Address the Associated Issues in the Cascading HGHG Scheme
Li-Hua Yu (BNL, Upton, Long Island, New York)

We discuss several experiments that can be carried out at BNL's DUVFEL to address several issues associated with cascaded HGHG FELs. These include: Chirped Pulse Amplification (CPA); HGHG with seed shorter than electron bunch length; 8th harmonic HGHG (from 800nm to 100nm); Regenerative synchronization of seed pulse and electron bunch; Tuning of HGHG without changing seed, proposed by Timur Shaftan; Cascading using NISUS and VISA: from 400nm to 100nm to 50nm. These experiments may have important impact on the development of multi-stage cascaded HGHG FELs.

MOAIS04 First Lasing at the ELBE mid-IR FEL
Peter Michel (Forschungszentrum Rossendorf, Dresden - Sachsen), Thomas Dekorsy, Pavel Evtushenko, Frank Gabriel, Eckart Grosse, Manfred Helm, Marcel Krenz, Ulf Lehnert, Wolfgang Seidel, Dietrich Wohlfarth, Andreas Wolf, Rudi Wuensch (FZR, Dresden)

First lasing of the mid infrared FEL at ELBE was achieved on May 7, 2004. The Radiation Source ELBE at the Forschungszentrum Rossendorf in Dresden is currently under transition from commissioning to regular user operation. Presently the electron linac produces an up to 18 MeV, 1 mA (cw) electron beam which is alotted to generate various kinds of secondary radiation. After the successful commissioning of the bremsstrahlung and channeling-X-ray facilities during 2003 stable lasing has now been observed in the IR range (15 to 22 μm). The oscillator FEL is equipped with two planar undulator units, both consisting of 34 hybrid permanent magnet periods of 27.3 mm (Krms = 0.3 - 0.8). The distance between the two parts is variable and the gaps can be adjusted and tapered independently. At 19.6 µm an optical power of 3W was out-coupled in a macro pulse of 0.6 ms duration using an electron beam energy of 16.1 MeV and an energy spread of less than 100 keV; the micropulse charge was 50 pC and its width slightly above 1ps. With the installation of a second acceleration module for additional 20 MeV smaller wavelengths will become available in the near future.

MOBIS01 Overview of Single Pass FEL Designs Technical Suggestions for Stability Improvement
Tsumoru Shintake (RIKEN Spring-8 Harima, Hyogo)

The talk will review recent achievement of technology development for SASE-FELs, such as the low emittance electron sources. The talk also gives some suggestion on "Background technology requirement for Single Pass FELs before or behind the "low emittance" story. Question is what do we need to prepare before starting the construction of a large scale machine?

MOBOS02 Scheme for Generation of Single 100 GW 300-as Pulse in the X-ray SASE FEL with the Use of a Few Cycles Optical Pulse from Ti:sapphire Laser System
Evgeny L. Saldin, Evgeny A. Schneidmiller, Mikhail V. Yurkov (DESY, Hamburg)

Femtosecond optical pulse interacts with the electron beam in the two-period undulator and produces energy modulation within a slice of the electron bunch. Then the electron beam enters the first part of the X-ray undulator and produces SASE radiation with 100 MW-level power. Due to energy modulation the frequency is correlated to the longitudinal position, and the largest frequency offset corresponds to a single-spike pulse in the time domain which is confined to one half-oscillation period near the central peak electron energy. After the first undulator the electron beam is guided through a magnetic delay which we use to position the X-ray spike with the largest frequency offset at the "fresh" part of the electron bunch. After the chicane the electron beam and the radiation enter the second undulator which is resonant with the offset frequency where only a single (300 as duration) spike grows rapidly. The final part of the undulator is a tapered section allowing to achieve maximum output power 100-150 GW in 0.15 nm wavelength range.

MOBOS03 An Experimental Study of the Beam-Steering Effect on the FEL Gain at LEUTL's Segmented Undulators
Yong-Chul Chae, Mark Erdmann, John W. Lewellen, Alex H. Lumpkin, Stephen Milton (ANL/APS, Argonne, Illinois)

The electron trajectories at the LEUTL, a SASE FEL facility at Argonne, were routinely corrected during the user run in order to deliver maximum radiation power to the user. Even though we knew from experience that SASE gain at the segmented undulators was dependent on the trajectory, the quantitative understanding of steering effects associated with the specific trajectory was lacking. Recently Tanaka et al. proposed an analytical model for the single-kick error (SKE) effect. Since LEUTL has eight segmented undulators, we performed the first measurement of SKE on the FEL gain. In the experiments we varied the corrector strength up to the critical angle, and the gain over the undulator was measured for each corrector setting. The results were compared with the analytical model and GENESIS simulations. We also measured the e-beam positions and SASE intensities over the undulators. The experimental data were analyzed and their results were reproduced by GENESIS simulation. The simulation condition, including the measured not-so-ideal trajectory, was used to predict performance enhancements that could be achieved by upgrading e-beam current, e-beam emittance, or trajectory control.

MOBOS04 Suppression of Microbunching Instability in the Linac Coherent Light Source
Zhirong Huang, Paul J Emma, C. Limborg-Deprey, Gennady Stupakov, Jim Welch, Juhao Wu (SLAC, Menlo Park, California), Michael Borland (ANL/APS, Argonne, Illinois)

A microbunching instability driven by longitudinal space charge, coherent synchrotron radiation, and linac wakefields is studied for the linac coherent light source (LCLS) accelerator system. Since the uncorrelated (local) energy spread of electron beams generated from a photocathode rf gun is very small, the microbunching gain may be large enough to significantly amplify rf-gun generated modulations or even shot-noise fluctuations of the electron beam. The uncorrelated energy spread can be increased by an order of magnitude to provide strong Landau damping against the instability without degrading the free-electron laser performance. We study different damping options in the LCLS and discuss an effective laser heater to minimize the impact of the instability on the quality of the electron beam.

MOBOS05 Generation of Narrow Linewidth X-rays by a Harmonic Cascade FEL
William S Graves, David Moncton (MIT/BLAC, Middleton, Massachusetts), William M. Fawley (LBNL/CBP, Berkeley, California)

The transform-limited bandwidth of a 1 ps laser pulse is 2 meV regardless of wavelength. For 1 Angstrom x-rays this corresponds to a relative bandwidth of less than 2.0e-7. While this bandwidth is similar to the best x-ray crystal monochromators, the peak brilliance of the beams would be over ten orders of magnitude higher than current third-generation synchrotron sources, offering unprecedented science opportunities. This long-pulse, narrow-bandwidth regime approaches the limit where all photons are in the same quantum state. We present time-dependent simulations of the evolution of a long coherent pulse in a harmonic cascade FEL, approaching the transform limit.

MOCOS03 Backward Wave Excitation and Generation of Oscillations in Distributed Gain Media and Free-Electron Lasers in the Absence of Feedback
Yosef Pinhasi, Yuri Lurie, Gad A. Pinhasi, Asher Yahalom (The College of Judea and Samaria, Ariel)

Quantum and free-electron lasers (FELs) are based on distributed interactions between electromagnetic radiation and gain media. In an amplifier configuration, a forward wave is amplified while propagating in a polarized medium. Formulating a coupled mode theory for excitation of both forward and backward waves, we identify conditions for phase matching, leading to efficient excitation of backward wave without any mechanism of feedback or resonator assembly. The excitations of incident and reflected waves are described by a set of coupled differential equations expressed in the frequency domain. The induced polarization is given in terms of an electronic susceptibility tensor. In quantum lasers the interaction is described by two first order differential equations, while in high-gain free-electron lasers, the differential equations are of the third order each. Analytical solutions of reflectance and transmittance for both quantum lasers and FELs are presented. It is found that when the solutions become infinite, the device operates as an oscillator, producing radiation at the output with no field at its input, entirely without any localized or distributed feedback.

MOCOS04 Nonlinear Harmonic Generation in Free-Electron Lasers with Helical Wigglers
Henry Freund (SAIC McLean, McLean), Sandra G. Biedron (ANL, Argonne, Illinois), Patrick Gerard O'Shea (IREAP, College Park, Maryland)

It is widely believed that harmonic generation is suppressed in helical wigglers. However, harmonic generation can occur in both planar and helical wigglers albeit by different mechanisms. Linear harmonic generation (LHG) in planar wigglers is due to harmonics in the axial velocity that excite linearly polarized, on-axis modes. In contrast, LHG in helical wigglers is due to an azimuthal resonance that excites circularly polarized, off-axis waves where the hth harmonic varies as exp(ihq). Nonlinear harmonic generation (NHG) is driven by nonlinear bunching at the fundamental and has different properties from LHG. While NHG has been studied in planar wigglers, there has been no analysis heretofore of NHG in helical wigglers. To this end, the 3-D simulation code MEDUSA has been modified to describe NHG in helical wigglers. A comparative analysis of NHG in planar and helical wigglers is presented. It is shown that NHG in helical wigglers excites on-axis modes with comparable intensities in the even and odd harmonics.

MOCOS05 CSRtrack: Faster Calculation of 3-D CSR Effects
Martin Dohlus, Torsten Limberg (DESY, Hamburg)

CSRtrack is a new code for the simulation of Coherent Synchrotron radiation effects on the beam dynamics of linear accelerators. It incorporates the physics of our previous code, TraFiC4, and adds new algorithms for the calculation of the CSR fields. A one-dimensional projected method allows quick estimates and a greens function method allows 3D calculations about ten times faster than with the `direct' method. The tracking code is written in standard FORTRAN77 and has its own parser for comfortable input of calculation parameters and geometry. Phase space input and the analysis of the traced particle distribution is done with MATLAB interface programs.

TUAIS01 Sub-Picosecond Electron Bunch Length Measurements at SLAC
Patrick Krejcik, Ron Akre (SLAC/LCLS, Menlo Park, California), Rasmus Ischebeck, Holger Schlarb (DESY, Hamburg), Paul J Emma, Mark J. Hogan (SLAC, Menlo Park, California), Jerry Hastings (SLAC/SSRL, Menlo Park, California), Patric Muggli (USC, Los Angeles, California), adrian Cavalieri (University of Michigan, Ann Arbor, Michigan)

The Sub-Picosecond Pulse Source (SPPS) built at SLAC uses a magnetic chicane to compress electron bunches to extremely short bunch lengths. The 28.5-GeV bunches of 3 nC charge transported to the test beam line can be as short as 80 fs fwhm, which poses a considerable instrumentation challenge for measuring the bunch length. This paper reviews the results obtained measuring such short bunches. Several techniques are compared in terms of their degree of invasiveness to the beam, single pulse versus average measurement of many bunches, capability to determine absolute bunch length versus relative measurement, and limits to achieving fs resolution. The techniques developed at SLAC range from a transverse RF deflecting cavity to electro-optic modulation of a fs laser pulse. Coherent radiation from the bunch is also used as a diagnostic of the bunch length. The power spectrum of THz coherent transition radiation is used to control the bunch length on pulse-by-pulse basis. Autocorrelation measurements of the coherent radiation to measure the average bunch length have also given much insight into the issues of propagating the THz radiation through windows and apertures.

TUAOS03 Large-Scale Timing Distribution and RF-Synchronization for FEL Facilities
Jung-Won Kim, Fatih Oemer Ilday, Franz Kaertner, Oliver Muecke, Michael Perrott (MIT, Cambridge, Massachusetts), William S Graves, David Moncton, Townsend Zwart (MIT/BLAC, Middleton, Massachusetts)

For future advances in accelerator physics in general and seeding of FELs in particular, precise synchronization between seed radiation, low-level RF-systems and photo-injector laser is required. Typical synchronization methods based on direct photodetection are limited by the detector nonlinearities, which lead to amplitude-to-phase conversion and introduce timing jitter. A new synchronization scheme for extraction of low jitter RF-signals from optical pulse trains distributed by mode-locked lasers is proposed. It is robust against photodetector nonlinearities. The scheme is based on a transfer of timing information into an intensity imbalance between the two output beams from a Sagnac-loop interferometer. As a first experimental demonstration, sub-100 fs timing jitter between the extracted 2 GHz RF-signal and the 100 MHz optical pulse train from a mode-locked Ti:sapphire laser is demonstrated. Numerical simulations show that scaling to sub-femtosecond precision is possible. Together with mode-locked fiber lasers and timing stabilized fiber-link, this scheme can be applied for the large-scale precise timing distribution and synchronization of free-electron laser facilities.

TUAOS04 High Temporal Resolution, Single-Shot Electron Bunch-Length Measurements
Giel Berden, Britta Redlich, Lex van der Meer (FOM Rijnhuizen, Nieuwegein), Steven Jamison (Strathclyde University, Glasgow), Allan Gillespie, Allan MacLeod (UAD, Dundee)

A new technique, combining electro-optic detection of the Coulomb field of an electron bunch with single-shot cross-correlation of optical pulses is used to enable single-shot measurements of the electric field profile of sub-picosecond electron bunches. As in our previous "spectral decoding" technique (I. Wilke et al., Phys. Rev. Lett. 88(12) 2002), the electric field of the electron bunch is encoded electro-optically on an optical pulse. However, the new "temporal decoding" method offers a much better time resolution since it overcomes a fundamental time-resolution limit of the spectral decoding method, which arises from the inseparability of time and frequency properties of the probing optical pulse. The temporal decoding technique has been applied to the measurement of 50 MeV electron bunches in the FELIX free electron laser, showing the longitudinal profile of single bunches of around 650 fs FWHM. The method is non-destructive and real-time, and therefore ideal for online monitoring of the longitudinal shape of single electron bunches. At FELIX we have used it for real-time optimization of sub-picosecond electron bunches.

TUAOS05 Gas-Monitor Detector for FEL Online Photon Beam Diagnostics
Mathias Richter, Alexander Gottwald (PTB, Braunschweig), Joseph Feldhaus, Ulrich Hahn, Kai Tiedtke (DESY, Hamburg), Sergei Bobashev (IOFFE, St. Petersburg), Andrei Alekseevich Sorokin (PTB, Braunschweig; IOFFE, St. Petersburg)

A gas-monitor detector based on the photoionization of rare gases was developed and successfully used for the non-destructive characterization of highly intense and extremely pulsed VUV free electron laser (FEL) radiation at the TESLA test facility (phase 1) in Hamburg. By first pulse resolved measurements, a peak power of more than 100 MW at a wavelength of 87 nm was detected. In order to provide online photon beam diagnostics of VUV-FEL radiation during phase 2 of the TTF project, a set of four new detectors has been constructed which are based on the prototype. The new detectors will not be used for intensity measurements only, but also for monitoring of the photon beam position. Each detector has been tested and calibrated in the Radiometry Laboratory of the Physikalisch-Technische Bundesanstalt at the electron storage ring BESSY II using spectrally dispersed synchrotron radiation at low intensities and a semiconductor photodiode as transfer standard. A conception for future gas-monitor detectors to characterize FEL radiation in the X-ray regime is also discussed.

TUBIS01 Attosecond X-ray Pulses in the LCLS using the Slotted Foil Method
Paul J Emma, Zhirong Huang (SLAC, Menlo Park, California), Michael Borland (ANL/APS, Argonne, Illinois)

A proposal has been made to generate femtosecond and sub-femtosecond x-ray pulses in the Linac Coherent Light Source (LCLS) SASE FEL by using a slotted spoiler foil located at the center of the second bunch compressor chicane. This previous study highlighted a simple case, using the nominal LCLS parameters, to produce a 2-fsec fwhm, 8-keV x-ray pulse. The study also pointed out the possibility of attaining sub-femtosecond pulses by somewhat modifying the LCLS compression parameters, but did not undertake a full tracking simulation for this more aggressive case. We take the opportunity here to study this `attosecond' case in detail, including a full tracking simulation, pushing the limit of the technique.

TUBOS05 Commissioning of the TTF Linac Injector at the DESY VUV-FEL
Katja Honkavaara (DESY, Hamburg)

The upgrade of the TESLA Test Facility (TTF) Linac at DESY is almost completed. With electron beam energies up to 1 GeV, it will be able to drive a new SASE FEL user facility (VUV-FEL) in the wavelength range from VUV to soft X-rays. The first phase of the redesigned photoinjector is finished. We report on its commissioning during spring 2004, including the first measurements of electron beam parameters. Since this injector is also a prototype for the XFEL injector, the results obtained are important for future SASE XFEL drive linacs.

TUCOS01 Status of the Novosibirsk Terahertz FEL
Nikolai Aleksandrovich Vinokurov, Vladimir Petrovich Bolotin, Dmitriy Aleksandrovich Kayran, Boris Aleksandrovich Knyazev, Evgeniy Ivanovich Kolobanov, V.V. Kotenkov, Vitaliy Vladimirovich Kubarev, Gennadiy Nikolaevich Kulipanov, Alexander Nikolaevich Matveenko, Lev Eduardovich Medvedev, Sergey Vladimirovich Miginsky, Leontiy Alekseevich Mironenko, Aleksandr Danilovich Oreshkov, Vladimir Kirillovich Ovchar, Vasiliy Mikhailovich Popik, Tatyana Vladimirovna Salikova, Mikhail Alekseevich Scheglov, Stanislav Sergeevich Serednyakov, Oleg Alexandrovich Shevchenko, Aleksandr Nikolayevich Skrinsky (BINP, Novosibirsk)

The first stage of Novosibirsk high power free electron laser (FEL) was commissioned in 2003. It is based on normal conducting CW energy recovery linac. Now the FEL provides electromagnetic radiation in the wavelength range 120 - 180 micron. The average power is 100 W. The measured linewidth is 0.3%, which is close to the Fourier-transform limit. The assembly of user beamline is in progress. Plans of future developments are discussed.

TUCOS03 VUV Optics Development for the Elettra Storage Ring FEL
Stefan Guenster, Detlev Ristau (LZH, Hannover), Francesca Sarto (ENEA, Roma), Miltcho B. Danailov, Mauro Trovò (Elettra, Basovizza, Trieste), Alexandre Gatto, Norbert Kaiser (IOF, Jena)

Vacuum ultraviolet optical components for the storage ring FEL at Elettra are under continuous development in the European research consortium EUFELE. Target of the project is the progress to shorter lasing wavelengths in the VUV spectral range. The current status allows lasing with oxide mirror systems down to 190 nm. The main obstacles for the development of optical coatings for shorter wavelengths is the high energetic background of the synchrotron radiation impinging onto the front mirror in the laser cavity. Investigations in single layer systems and multilayer stacks of oxide or fluoride materials demonstrate that fluoride mirrors reach highest reflectivity values down to 140 nm, and oxide coatings possess a satisfactory resistance against the high energetic background irradiation. However, pure oxide multilayer stacks exhibit significant absorption below 190 nm and pure fluoride stacks suffer from strong degradation effects under synchrotron radiation. A solution could be hybrid systems, combining fluoride stacks with oxide protection layers to provide high reflectivity and a robust behaviour under synchrotron radiation load. Results of hybrid systems will be presented.

TUCOS04 Coherent Harmonic Generation using the ELETTRA Storage Ring Optical Klystron
Giovanni De Ninno, Miltcho B. Danailov, Bruno Diviacco, Mario Ferianis, Mauro Trovò (Elettra, Basovizza, Trieste), Luca Giannessi (ENEA C.R. Frascati, Frascati - Roma)

The standard process leading to CHG using single-pass devices or storage rings is based on the up-frequency conversion of a high-power laser focused into the first undulator of an optical klystron. The seeding signal, which is necessary to produce the modulation of the electron density and hence to induce the coherent emission, may be provided by an external laser or, in the case of storage-ring oscillators, by the FEL itself. The latter configuration has been recently implemented at ELETTRA allowing to generate the third harmonic of an intra-cavity signal at 660 nm. In the first part of this paper, we report about the set of measurements that have been performed, for different experimental set-ups, with the aim of characterizing the power as well as the spectral and temporal characteristics of the obtained radiation. As for seeding using an external laser, a detailed campaign of simulations, reported in the second part of the paper, shows that the ELETTRA optical klystron is also well suited for the investigation of this configuration. These results make the ELETTRA FEL an ideal test-facility in view of CHG experiments planned on dedicated next-generation devices.

TUCOS05 Short Rayleigh Length Free Electron Lasers
William B. Colson, Robert L. Armstead, Joseph Blau, Peter P. Crooker (NPS, Monterey, CA)

Conventional free electron laser (FEL) oscillators minimize the optical mode volume around the electron beam in the undulator by making the resonator Rayleigh length about one third of the undulator length. This maximizes gain and beam-mode coupling. In compact configurations of high-power infrared FELs or moderate power UV FELs, the resulting optical intensity can damage the resonator mirrors. To increase the spot size and thereby reduce the optical intensity at the mirrors below the damage threshold, a shorter Rayleigh length can be used, but the FEL interaction is significantly altered. A new FEL interaction is described and analyzed with a Rayleigh length that is only one tenth the undulator length, or less. The effect of mirror vibration and positioning are more critical in the short Rayleigh length design, but we find that they are still within normal design tolerances.

WEAIS01 Experimental Demostration of Wavelength Tuning in High-Gain Harmonic Generation Free Electron Laser
Timur Shaftan, Erik Johnson, Sam Krinsky, Henrik Loos, James Murphy, George Rakowsky, James Rose, Brian Sheehy, John Skaritka, Xijie Wang, Zilu Wu, Li-Hua Yu (BNL/NSLS, Upton, Long Island, New York)

We present experimental results on tuning of the HGHG FEL output wavelength while holding the input seed wavelength constant. Using compression of the initially chirped beam in the HGHG dispersion section we have measured the wavelength shift of about 1% around the nominal value of 266 nm. The tuning range is expected to reach 3 % after the dispersive section upgrade at the DUV FEL. An optimized design based on this principle, using additional linac sections, would have the capability of providing full tunability.

WEAOS02 Spectral Phase Modulation and chirped pulse amplification in High Gain Harmonic Generation
Zilu Wu, Erik Johnson, Sam Krinsky, Henrik Loos, James Murphy, Timur Shaftan, Brian Sheehy, Yuzhen Shen, Xijie Wang, Li-Hua Yu (BNL/NSLS, Upton, Long Island, New York)

High Gain Harmonic Generation (HGHG), because it produces longitudinally coherent pulses derived from a coherent seed, presents remarkable possibilities for manipulating FEL pulses. If spectral phase modulation imposed on the seed modulates the spectral phase of the HGHG in a deterministic fashion, then chirped pulse amplification, pulse shaping, and coherent control experiments at short wavelengths become possible. In addition, the details of the “transfer function” will likely depend on electron beam and radiator dynamics and so prove to be a useful tool for studying these. Using the DUVFEL at the National Synchrotron Light Source at Brookhaven National Laboratory, we present spectral phase analyses of both coherent HGHG and incoherent SASE ultraviolet FEL radiation, applying Spectral Interferometry for Direct Electric Field Reconstruction (SPIDER), and assess the potential for employing compression and shaping techniques.

WEAOS03 Dynamical Analysis of Chaos Generated on a Storage Ring Free Electron Laser
Christelle Bruni, Marie-Emmanuelle Couprie, David Garzella, Gian Luca Orlandi (LURE, Orsay), Dalila Amroun, Christophe Letellier (Université de Rouen, Saint Etienne du Rouvray)

Chaos could be generated on a FEL by applying a modulation on the gain, which frequency is near the resonance one of the system. Systematic studies of the macro-temporal structures show that windows of chaos appear according to the frequency and the amplitude of the modulation. The evolution of the system is reproduced by a numerical code based on a system of differential equations. It describes pass to pass in the optical klystron, the laser intensity and the energy spread evolution. The dynamical analysis is realised by underlying the topology of the phase-space portrait built from the laser intensity time series. The experimental dynamics is compared to the dynamics of the model.

WEAOS04 Study of Coherence Limits and Chirp Control in Long Pulse FEL Oscillator
Avraham Gover, Alon Eliran, Yehoshua Socol, Mark Volshonok (University of Tel-Aviv, Tel-Aviv), Moshe Einat, Miki Kanter, Boris Yu Kapilevich, B. Litvak, Yuri Lurie, Yosef Pinhasi, Asher Yahalom (The College of Judea and Samaria, Ariel)

Electrostatic Accelerator FELs have the capacity to generate long pulses of tens microseconds and more, that in principle can be elongated indefinitely (CW operation). This allows the generation of very coherent radiation. The fundamental linewidth is extremely narrow [1], and in practice the spectral width is limited by the pulse duration (Fourier transform limit) and e-beam stability. Practical problems such as the accelerator terminal voltage drop due to a non-ideal electron beam transport may reduce the length of the radiation pulse and hence create a limiting factor for coherence measurement. The current status of the Israeli Tandem Electrostatic Accelerator FEL allows the generation of pulses of tens microseconds duration. It has been operated recently past saturation, and produces single mode coherent radiation of relative linewidth ~Δf/f=10-5 at frequencies near 100GHz. A clear frequency chirp is observed during pulses of tens of microseconds (0.1-1 MHz/mS), and is directly proportional to the voltage drop rate of the High-Voltage terminal. We will report experimental studies of the spectral linewidth and chirp characteristics of the radiation, along with theory and numerical simulations, carried out using space-frequency model [2], matching the experimental data.

WEAOS05 Measuring the Double-Differential Spectrum of Ultra-Short SASE Radiation Pulses at VISA FEL
Alex Murokh, Gerard Andonian, Sven Reiche (UCLA/DPA, Los Angeles - California), Yakimenko Vitaly (BNL, Upton, Long Island, New York), C. Vicario (INFN/LNF, Frascati (Roma)), James B Rosenzweig, Gil Travish (UCLA, Los Angeles, California)

In recent years, there have been numerous publications related to the generation of femtosecond radiation pulses with SASE FEL. In VISA II experiment at BNL, experimental studies were undertaken to characterize the emission properties of the short pulses generated by strongly compressed single spike electron beam. Strong deviation from a continuous beam model was found in angular, spectral and gain evolution properties of such radiation. Simultaneous measurements of angular and spectral distributions was performed and results are compare to theoretical and simulation models.

WEBOS01 Current-Enhanced SASE Using an Optical Laser and its Application to the LCLS
Alexander A Zholents, William M. Fawley (LBNL/CBP, Berkeley, California), Paul J Emma, Zhirong Huang, Gennady Stupakov (SLAC, Menlo Park, California), Sven Reiche (UCLA/DPA, Los Angeles - California)

We propose a significant enhancement of the electron peak current entering a SASE undulator by inducing an energy modulation in an upstream wiggler magnet via resonant interaction with an optical laser, followed by micro-bunching of the energy-modulated electrons at the accelerator exit. This current enhancement allows a considerable reduction of the FEL gain length. The x-ray output consists of a series of uniformly spaced spikes, each spike being temporally coherent. The duration of this series is controlled by the laser pulse and in principle can be narrowed down to just a single, ~100-attosecond spike. Given potentially absolute temporal synchronization of the x-ray spikes to the energy-modulating laser pulse, this scheme naturally makes pump-probe experiments available to SASE FEL’s. We also study various detrimental effects related to the high electron peak current and discuss potential cures. We suggest a possible operational scenario for the LCLS optimized with respect to the choice of the modulating laser beam and electron beam parameters. Numerical simulations are provided.

WEBOS02 Generation of Terahertz Radiation by Modulating the Electron Beam at the Cathode
Jonathan Neumann, Ralph Fiorito, Patrick Gerard O'Shea (IREAP, College Park, Maryland), G.L. Carr (BNL, Upton, Long Island, New York), Henrik Loos, Timur Shaftan, Brian Sheehy, Yuzhen Shen, Zilu Wu (BNL/NSLS, Upton, Long Island, New York), Henry Freund (SAIC McLean, McLean)

A bunched electron beam can be used to generate coherent radiation in a particle accelerator. This experiment, a collaboration between the University of Maryland and the Source Development Laboratory at Brookhaven National Laboratory, uses a drive laser modulated at terahertz frequencies in an RF-photoinjecting electron accelerator to produce a bunched beam at the cathode. The experiment is designed to determine if such a scheme could be used to develop a compact, high power terahertz emitter. After acceleration to approximately 72 MeV, a mirror intercepts the beam. The backwards transition radiation from the mirror is measured with a bolometer. The experiment was conducted at various modulation frequencies and levels of charge.

WEBOS04 Potential Use of eRHIC’s ERL for FELs and Light Sources
Vladimir N. Litvinenko, Ilan Ben-Zvi (BNL, Upton, Long Island, New York)

One of the design of future electron-hadron collider eRHIC* is based on a 5-10 GeV high current energy-recovery linac (ERL) with possible extension of its energy to 20 GeV. This ERL will operate with high brightness electron beams, which do naturally match requirements for X-ray FELs and other next generation light sources. In this paper we present a number of possible scenarios which use eRHIC ERL in parasitic and dedicated mode for SASE, HGHG and oscillator X-ray FELs. We explore a possibility of optic-free X-ray oscillator in detail.

WEBOS05 The Harmonically Coupled 2-Beam FEL
Brian W.J. McNeil, Gordon Robb (Strathclyde University, Glasgow), Mike Poole (CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire)

A 1-D model of a 2-beam Free Electron Laser amplifier is presented. The two co-propagating electron beams have different energies, chosen so that the fundamental resonant FEL interaction of the higher energy beam is at an harmonic of the lower energy beam. In this way, a coupling between the FEL interactions of the two beams occurs via the harmonic components of the electron bunching and radiation emission of the lower energy interaction. Such resonantly coupled FEL interactions may offer potential benefits over existing single beam FEL schemes. A simple example is presented where the lower energy FEL interaction only is seeded with radiation at its fundamental resonant wavelength. It is predicted that the coherence properties of this seed field are transfered via the resonantly coupled FEL interaction to the un-seeded higher energy FEL interaction, thereby improving its coherence properties over that of a SASE interaction alone. This method may offer an alternative seeding scheme for FELs operating in the XUV and x-ray regions of the spectrum.

THAIS01 Coherent XUV Radiation with Conventional Lasers
Philippe Zeitoun, Philippe Balcou, Frederique Burgy, Denis Douillet, Gregory Faivre, Abdesselem Hallou, Thierry Lefrou, Pascal Mercère, Tomas Mocek, Anne-Sophie Morlens, Jean-Philippe Rousseau, Stéphane Sebban, Constance Valentin (LOA, Palaiseau), Damien Aubert, Gaetan de Lachèze-Murel (CEA/DIF, Bruy\`{e}res-le-Ch\^{a}tel), Marta Fajardo, H. Merdji (IST-FP, Lisboa), Sophie Kazamias (LSAI, Orsay), Sebastien le Pape (Laboratoire pour l’Utilisation des Lasers Intenses, Palaiseau)

For about thirty years, lasers have been used to produce laser-like emission in the XUV spectral range (typically 4-60 nm). During the late 90’s, independantely High harmonics generation (HHG) and soft x-ray lasers (SXRL) have reached the level of stability and reproducibility for being run on applications experiment. The first source inherits from very short pulse duration as short as 100 attosecond, good optical beam quality but with a low energy per pulse. Soft x-ray lasers demonstrated pulse energy as high as 10 mJ at 21.2 nm but with lower optical quality and longer pulse duration (from 2 to 80 ps FWHM). A very recent experiment as demonstrated that seeding a soft x-ray laser with HHG generates high energy pulse while keeping the HHG beam quality. Numerical modelling shows that seeded soft x-ray lasers may reach the mJ level with pulse duration around 100 fs. These sources (HHG, SXRL and seeded SXRL) are complementary from VUV-FEL for many experiments.

THAIS02 SPPS: New Science on the Way to LCLS
Aaron M. Lindenberg (SLAC/SSRL, Menlo Park, California)

We report new results from the Subpicosecond Pulse Source (SPPS) demonstrating the ability of accelerator-based x-ray sources to resolve atomic-scale motion with femtosecond temporal resolution. It is shown that the short-time-scale dynamics associated with ultrafast melting of solids is inertial in character, pointing to analogies with the intrinsic dynamics of equilibrium liquids.

THAIS03 Advancing Terahertz Science and Technology with the UCSB Free-electron Lasers
S. James Allen (UCSB, Santa Barbara)

The UCSB free-electron lasers deliver kilowatts of coherent terahertz radiation that can be tuned from ~140 GHz to 4.8 THz with pulse widths that can be controlled and varied from 10’s of microsconds to several picoseconds. This unique source has made possible a wide variety of experiments on terahertz electro-optics, coherent quantum control, photon assisted transport, terahertz device physics, terahertz material properties, non-equilibrium dynamics, and non-linear dynamics. A compilation of the work at UCSB documented through 2001 can be found at Here we will focus on recent efforts on terahertz coherent quantum control, terahertz electro optics and device physics.

THBOC02 Recent Results and Perspectives of the Low Emittance Photo Injector at PITZ
Frank Stephan, Juergen Baehr, Ulrich Gensch, Hans-Juergen Grabosch, Jang Hui Han, Mikhail Krasilnikov, Dirk Lipka, Velizar Miltchev, Anne Oppelt, Bagrat Petrosyan, Dietrich Pose, Sabine Riemann, Lazar Staykov (DESY Zeuthen, Zeuthen), Michael von Hartrott, Eberhardt Jaeschke, Dieter Krämer, Dieter Richter (BESSY GmbH, Berlin), Galina Asova, Gancho Dimitrov (DESY Zeuthen, Zeuthen; INRNE, Sofia), Karen Abrahamyan (DESY Zeuthen, Zeuthen; YerPhI, Yerevan), Ilja Bohnet, Jean-Paul Carneiro, Klaus Floettmann, Siegfried Schreiber (DESY, Hamburg), Paolo Michelato, Laura Monaco, Carlo Pagani, Daniele Sertore (INFN/LASA, Segrate (MI)), Ivan Tsakov (INRNE, Sofia), Wolfgang Sandner, Ingo Will (MBI, Berlin), Wolfgang Ackermann, Wolfgang F.O. Mueller, S. Schnepp, Stefan Setzer, Thomas Weiland (TU Darmstadt, Darmstadt), Joerg Rossbach (Uni HH, Hamburg)

The Photo Injector Test Facility at DESY Zeuthen (PITZ) was built to study the production of minimum transverse emittance electron beams for Free Electron Lasers. In November 2003 the electron beam from the RF gun was fully characterized at PITZ. For a bunch charge of 1 nC a minimum normalized projected beam emittance of 1.5 π mm mrad in the vertical plane and a minimum geometrical average of both transverse planes of 1.7 π mm mrad have been achieved. This fulfils the requirements of the VUV-FEL at DESY Hamburg. In this contribution an overview on the measured electron beam and high duty cycle RF parameters including transverse emittance, thermal emittance, bunch length, momentum and momentum spread will be given. In addition, planned major upgrades and first results towards fulfilling the even more challenging requirements for the European XFEL will be discussed. This includes the increase of the accelerating gradient on the photo-cathode and the improvement of the transverse and longitudinal laser beam parameters.

THBOC03 Emittance Measurement on the CeB6 Electron Gun for the SPring-8 Compact SASE Source
Kazuaki Togawa, Hitoshi Baba, Takahiro Inagaki, Kazuyuki Onoe, Tsumoru Shintake, Takashi Tanaka (RIKEN Spring-8 Harima, Hyogo), Hiroshi Matsumoto (KEK, Ibaraki)

A high-volatage pulsed electron gun has been constructed for the injector system of the soft X-ray FEL project at SPring-8 (SCSS project). A CeB6 single crystal was chosen as a thermionic cathode, because of its excellent emission properties. The gun voltage of -500 kV was chosen to reduce emittance growth due to space charge. We have succeeded in generating a 500 keV beam with 1 A peak current and 3 micro-sec FWHM. The beam was very stable with low jitter. The beam emittance has been measured by means of double-slits method, and the normalized rms emittance of 1.1 pi-mm-mrad has been obtained. We report on the experimental result on the emittance measurement of the CeB6 electron gun.

THBOC04 Ampere Average Current Photoinjector and Energy Recovery Linac
Ilan Ben-Zvi, A. Burrill, R. Calaga, P. Cameron, X. Chang, D. Gassner, H. Hahn, A. Hershcovitch, H.C. Hseuh, P. Johnson, D. Kayran, J. Kewisch, R. Lambiase, Vladimir N. Litvinenko, G. McIntyre, A. Nicoletti, J. Rank, T. Roser, J. Scaduto, K. Smith, T. Srinivasan-Rao, K.-C. Wu, A. Zaltsman, Y. Zhao (BNL, Upton, Long Island, New York), H. Bluem, A. Burger, Mike Cole, A. Favale, D. Holmes, John Rathke, Tom Schultheiss, A. Todd (AES, Medford, NY), J. Delayen, W. Funk, L. Phillips, Joe Preble (Jefferson Lab, Newport News, Virginia)

High-power Free-Electron Lasers were made possible by advances in superconducting linac operated in an energy-recovery mode, as demonstrated by the spectacular success of the Jefferson Laboratory IR-Demo. In order to get to much higher power levels, say a fraction of a megawatt average power, many technological barriers are yet to be broken. BNL’s Collider-Accelerator Department is pursuing some of these technologies for a different application, that of electron cooling of high-energy hadron beams. I will describe work on CW, high-current and high-brightness electron beams. This will include a description of a superconducting, laser-photocathode RF gun employing a new secondary-emission multiplying cathode and an accelerator cavity, both capable of producing of the order of one ampere average current.

THBOC05 Status of the 3 1/2 Cell Rossendorf Superconducting RF Gun
Dietmar Janssen, Hartmut Buettig, Pavel Evtushenko, Ulf Lehnert, Peter Michel, Christof Schneider, Juergen Stephan, Jochen Teichert (FZR, Dresden), Slava Kruchkov, Oleg Myskin, Vladimir Volkov (BINP, Novosibirsk)

In Rossendorf it was shown for the first time that a RF electron gun where a photo cathode is inside a superconducting cavity, works stable over a period of seven weeks. At 4.2K no change of the quality factor Q = 2.5 108 has been observed [1]. The experimental results were the basis for the design of a new 3.4 cell superconducting RF photo electron gun [2]. The paper presents details of different components of this gun, explains the status of manufacturing and gives results of first test measurements. Furthermore, the idea is discussed to use for emittance compensation instead of a static magnetic field which is inside the cavity of a normal conducting RF gun in the superconducting gun cavity an additional magnetic RF field (TE011 mode) . By computer simulation the attraction of this idea is demonstrated.

THBOS01 Generation of Surface Electromagnetic Waves by Free-Electron Laser Terahertz Radiation and their Refractive Index Determination
Guerman N. Zhizhin (RAS/STC UI, Moscow), Grigori M. Kazakevitch (BINP, Novosibirsk), Guenrikh D. Bogomolov, Vitaliy V. Zavyalov (IPP, Moscow), Young Uk Jeong, Byung Cheol Lee (KAERI, Daejon)

In this paper we discuss the perspective of combined use of plane waves along with the surface electromagnetic waves (SEW) for interferometric studies of metals’ optical properties. Recently we succeeded in the experiments on the SEW generation and on use of them for interferometric determination of light phase velocity in the wavelength range of λ=110-150 μm by using a wide-band THz FEL in KAERI. The interference technique employing SEW propagation in the part of one shoulder of asymmetric phase interferometer was applied. From the interference pattern the real part of SEW’ effective refraction index was determined for laser emission wavelengths: for λ=150 μm –it is 1+5·10-5, for λ=110 μm –it is 1+8·10-4. The high sensitivity of interference pattern to overlayers of Ge and of Si having thickness 100 nm was demonstrated as well. The interference pattern was recorded by a liquid helium cooled Ge:Ga detector. FEL radiation arrived the input of experimental set-up in the form of macropulses with duration of 3 μs (10 W at λ=110 μm) and repetition period of 1-10 Hz, while registered radiation intensity(normalized on independently measured beam intensity) was averaged over 8 sequential pulses.

THBOS03 THz Imaging by a Wide-band Compact FEL
Young Uk Jeong, Hyuk Jin Cha, Byung Cheol Lee, Seong Hee Park (KAERI, Daejon), Grigori M. Kazakevitch (BINP, Novosibirsk)

We have developed a laboratory-scale users facility with a compact THz FEL. The FEL operates in the wide wavelength range of 100–1200 μm, which corresponds to 0.3-3 THz. THz radiation from the FEL shows well collimated Gaussian spatial distribution and narrow spectral width of 0.3 μm, which is Fourier transform limited by the estimated pulse duration of 20 ps. The main application of the FEL is THz imaging for bio-medical researches. We are developing THz imaging techniques by 2-D scanning, single pulse capturing with the electro-optic method, and 3-D holography. High power, coherent, and pulsed feature of the FEL radiation is expected to show much better performance in advanced THz imaging of 3-D tomography by comparing with incoherent and weak THz sources. By controlling the optical delay between reference beam and scattered light from an object, we can get its 3-D tomography by the holograms. The coherent and pulse length of the FEL beam is measured to be 3-6 mm. In this paper we will show and discuss the main results of THz imaging with the different methods by using the KAERI compact FEL.

THCIS01 Proposals for Pump-Probe Experiments in the Gas Phase using the TTF2-FEL
Michael Meyer (LURE, Orsay)

Many processes induced by the interaction of XUV light with atoms and molecules take place on a very short time scale. The temporal width of the soft X-Ray FEL pulses (100-300 fs) and of the synchronized, tunable optical laser (150 fs) will therefore be ideally suited to gain an insight into the dynamics of these processes. A first series of proposed experiments will serve to characterize the FEL pulses themselves, in particular the intensity, frequency and time structure of the individual pulses by using a cross correlation technique between the XUV photons and a strong infrared pulse. Depending on the final characteristics of the FEL with respect to photon energy range and tunability, these two-photon pump-probe experiments will be extended to further studies, like the investigation of resonances, which are only accessible by a two-photon excitation, the coupling of autoionization states by a strong laser field, which induces drastic changes in the resonance profiles, the wavepacket formation of higher Rydberg states, and the coherent population of excited states by fast dissociation, which will result in the observation of quantum beats on the decay curve of excited fragments.

THCOS02 Interaction of Intense Ultrashort XUV Pulses with Different Solids – Results from the Tesla Test Facility FEL Phase I
Jacek Krzywinski, Marek Jurek, Dorota Klinger, Jerzy Pelka, Andrzej Wawro (IP PAS, Warsaw), Marcin Sikora (AGH University of Science and Technology, Krakow), Evgeny L. Saldin, Evgeny A. Schneidmiller, Barbara Steeg, Rolf Treusch, Mikhail V. Yurkov (DESY, Hamburg), Michal Bittner, Dagmar Chvostova, Libor Juha, Vit Letal, Vladimir Vorlicek (FZU, Prague), Andrzej Andrejczuk, Henryk Reniewicz (University of Bialystok, Bialystok), Ryszard Sobierajski (Warsaw University of Technology, Warsaw), Anna Kauch (Warsaw University, Warsaw)

Desorption, ablation, and plasma formation have been studied for a large variety of materials (insulators, semiconductors, and metals). Damaged surfaces have been investigated using light, electron, and atomic force microscopy. Short-wavelength ablation was very efficient and clean when proper irradiation conditions were chosen. The edges of craters were sharp, and the area around the craters was clean. A distinct difference in the behavior of conducting materials and insulators was observed. In the case of insulators the morphology of the irradiated surface and the crater depth hardly depended on the beam intensity. In contrast, the irradiated silicon surface becomes very rough when the intensity exceeds the damage threshold. At high intensities multiple charged ions were registered. Kinetic energy of the ions increases with charge state and reaches keV range for highly-charged ions. Again, a clear difference between insulators and conducting material was observed. High charge states and energetic ions were typical for conductors and semiconductors. Only single ions states and low energetic ions (~50 eV) were detected for insulators for all irradiation conditions.

FRAIS01 Advances in the Physical Understanding of Laser Surgery at 6.45 microns
Michael Shane Hutson (Vanderbilt/DPA, Nashville - Tennessee), Glenn Edwards (DU/FEL, Durham, North Carolina)

We previously presented a model that attributes the wavelength-dependence of FEL tissue ablation to partitioning of absorbed energy between protein and saline. This energy-partitioning subsequently influences the competition between protein denaturation and saline vaporization. The original model approximated cornea as a 1D laminar material with a 50:50 saline-to-protein volume ratio. We have now refined the microscopic geometry of the model in two important ways: (1) cornea is represented as a saline bath interpenetrated by a 2D hexagonal array of protein fibrils; (2) the volume ratio is matched to the measured value, 85:15. With this volume fraction, the specific absorption coefficient for protein is much larger than previously reported. Thus, the 2D model magnifies the differences between wavelengths that target protein, as opposed to saline. We will discuss: (1) the consistency of this model with previous, seemingly conflicting, experimental data; (2) predictions of the model, with a particular emphasis on the role of laser intensity; and (3) the experiments needed to test these predictions.

FRAOS02 Two-Color Mid-IR Pump-Probe Spectroscopy of Myoglobin and Corneal Stroma
George A. Marcus, H. Alan Schwettman, Dmitri M. Simanovskii (HEPL-FEL, Stanford)

The study of protein vibrational dynamics provides a window into protein behavior and tissue ablation. Energy deposited in the protein amide modes can equilibrate with the solvent thermal bath indirectly via Intramolecular Vibrational Relaxation (IVR) or directly via intermolecular relaxation. An IVR dominated pathway may have a bottleneck, causing long relaxation times. Vibrationally excited proteins can be created by pumping amide I or II modes, each of which have different absorption strengths relative to the overlapping water bend mode. By probing the transient protein absorption, we can monitor energy trapped within the protein. Conversely, by probing transient absorption in the water association band, we can monitor the arrival of energy in the thermal bath. Thermal diffusion provides an upper bound for the timescale of the energy equilibration process. In Myoglobin, the thermal diffusion time is about 10 ps. For corneal stroma, made up of alternating layers of collagen fibers and water, the thermal diffusion time is on the order of 1 ns. Two-color mid-IR pump-probe spectroscopy experiments, using an OPA synchronized to the Stanford FEL will be described.

FRBIS01 The European X-ray Free Electron Laser Project at DESY
Andreas Schwarz (DESY, Hamburg)

On February 5, 2003, the German Federal Ministry of Education and Research decided that the X-ray free-electron laser XFEL, proposed by the International TESLA Collaboration, should be realized as a European project and located at DESY/Hamburg. The ministry also announced that in view of the locational advantage, Germany is prepared to cover half of the investment and personnel costs for the XFEL. In the course of the last year work has concentrated on the following areas: setting up of an organizational structure at DESY for the preparation of the project, discussions with potential European partners on several levels, selection of a new site for the XFEL facility and the preparation of the 'plan approval procedure'. The present status of the technical layout of the Linear Accelerator, the SASE Undulator and Photon Beamlines and the experiment stations will be presented.

FRBIS03 FEL Developments and Trends: A Personal Observation of FEL2004
Mike Poole (CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire)

A personal impression of the conference in the framework of the ongoing activities in the field.