TUPP :: Tuesday Afternoon Poster Session

Date/Time: 23-Aug-05 :: 13:45—15:45
Chair: C. Pellegrini, UCLA, Los Angeles, California

Paper Title Page
TUPP001 Light Phase and Group Velocity in FEL
 
  • S.G. Oganesyan, G.S. Oganesyan
    LT CSC, Yerevan
 
 

We have studied dispersion properties of an electron beam in FEL. The case of a long undulator and small electron density was analyzed on the basis of the Klein-Gordon and wave equations. We have obtained that the FEL operating bandwidth is directly proportional both to the electromagnetic pulse carried frequency and the electron beam relative energy spread width. That made it possible to introduce the definition of a long pulse (its spectral width is less then operating bandwidth) and a short pulse (on the contrary). We have studied the long pulse phase and group velocity when the carried frequency wave is under maximum amplification and maximum absorption. It has been discovered that in both regimes the phase velocity exceeds the light velocity in a vacuum, i.e., c. Hence the beam is like plasma. We find that the pulse group velocity however depends on the FEL regime. In the amplification regime its quantity exceeds the c, while in the absorption one it is less then the c. From viewpoint of this result the electron beam is already similar to a resonant atomic medium.

 
   
TUPP002 Controlling over Superintense Electromagnetic Pulse Parameters with FEL
 
  • S.G. Oganesyan, G.S. Oganesyan
    LT CSC, Yerevan
 
 

We have studied propagation of a Gaussian electromagnetic pulse through a long FEL. Our analysis is based on the Maxwell and Klein-Gordon equations and takes into account both the active and dispersive properties of an electron beam. The laser output in (a) linear and (b) nonlinear complex phase regimes has been considered. We obtained expressions for FEL operative bandwidth and characteristic time, and introduced conception of long and short pulses. We have discovered a stabilization effect in the case (a). Namely, short pulses with random initial lengths have the same ones after coupling. The Rayleigh regions caused by dispersion and amplification (absorption) are obtained for long pulse in the case (b). If the carried frequency is under maximum gaining, then one observes only the pulse expansion. The most interesting effects have been discovered in the absorption regime. Here the FEL can operate as a slight compressor or as an explosive stretcher. Besides, FEL device makes it possible the chirping of pulses. Thus FEL might be employed for controlling over superintense ultra short pulses, which damage ordinary media

 
   
TUPP003 Quantum Signatures in Laser-Assisted Cherenkov Radiation
 
  • H.K. Avetissian, S.S. Israelyan, G.F. Mkrtchian, Kh.V. Sedrakian
    YSU, Yerevan
 
 

If in the spontaneous radiation processes of charged particles the medium with refractive index n>1 plays only a role of the third body, the presence of a medium at the interaction with external electromagnetic wave causes the new threshold phenomena which have an essentially nonlinear character. In the present work the case of strong laser field is considered within the scope of the relativistic quantum theory for electron-laser interaction in a medium. Using Strong Coupled State approximation the spectrum of eigenvalues of particle energy (in the rest frame of the wave) and the wave function is found. Due to the nonlinear resonant interaction with given laser field the equidistant levels of longitudinal motion are formed and as a consequence the spontaneous transitions from the upper levels take place with the emission of corresponding quanta. In the scope of Quantum Electrodynamics the spectral intensity of laser-assisted Cherenkov radiation is obtained. The first-order Feynman diagram is calculated where the electron lines correspond to the wave functions in the strong laser field and the resonant interaction is discussed.

 
   
TUPP004 Quantum SASE Regime for X-Ray FEL
 
  • H.K. Avetissian, G.F. Mkrtchian
    YSU, Yerevan
 
 

For the X-ray FEL if the amplifying photon energy is larger or comparable to resonance widths caused by an electron beam spreads or by the finite interaction length then the quantum effects may play a significant role [1] and the generation process shifts from the classical to the quantum regime. The recent advancement of high brightness particle and laser beams technology makes achievable the fulfillment of these conditions in the scheme of X-ray Backscatter Compton laser. In this work we consider in general the SASE X-ray FEL in the quantum regime of amplification arising from the self-consistent set of the Maxwell and relativistic quantum kinetic equations. It is shown a considerable increase in start-up and narrowing of the spectrum of the SASE power for amplifying X-ray frequencies compared with the classical SASE regime.

[1] H.K. Avetissian, G.F. Mkrtchian, Phys. Rev. E 65, 046505 (2002).

 
   
TUPP005 Misconceptions regarding Second Harmonic Generation in X-Ray Free-Electron Lasers 254
 
  • G. Geloni, E. Saldin, E. Schneidmiller, M.V. Yurkov
    DESY, Hamburg
 
 

Nonlinear generation of coherent harmonic radiation is an important option in the operation of a X-ray FEL facility since it broadens the spectral range of the facility itself, thus allowing for a wider scope of experimental applications. We found that up-to-date theoretical understanding of second harmonic generation is incorrect. Derivation of correct radiation characteristics will follow our criticism.

 
   
TUPP006 Influence of an Energy Chirp on SASE FEL Operation 258
 
  • E. Saldin, E. Schneidmiller, M.V. Yurkov
    DESY, Hamburg
 
 

Influence of a linear energy chirp, imposed on the electron beam, on SASE process is studied analytically and numerically.

 
   
TUPP007 Simulation of a Smith-Purcell FEL Using a Particle-in-Cell Code
 
  • J.T. Donohue
    CENBG, Gradignan
  • J. Gardelle
    CESTA, Le Barp
 
 

A simulation of the generation of Smith-Purcell (S-P) radiation at microwave frequencies is performed using the two-dimensional particle-in-cell code MAGIC. The simulation supposes that a continuous, thin (but infinitely wide), mono-energetic electron beam passes over a diffraction grating, while a strong axial magnetic field constrains the electrons to essentially one-dimensional motion. We find that the passage of the beam excites an evanescent electromagnetic wave in the proximity of the grating, which in turn leads to bunching of the initially continuous electron beam. The frequency and wave number of the bunching are determined, and found to be close to those proposed by Brau and co-workers in recent work [1]. This frequency is below the threshold for S-P radiation. However, the bunching is sufficiently strong that higher harmonics are clearly visible in the beam current. These harmonic frequencies correspond to allowed S-P radiation, and we see strong emission of such radiation at the appropriate angles in our simulation, again in agreement with Brau's predictions. The bunching displays exponential growth both in time and space; the imaginary parts of the frequency and wave number are studied as functions of beam current.

[1] H. L. Andrews and C. A. Brau, Phys. Rev. ST Accel. Beams 7, 070701 (2004)

 
   
TUPP008 Simulation of Smith-Purcell Terahertz Radiation Using a Particle-in-Cell Code 262
 
  • J.T. Donohue
    CENBG, Gradignan
  • J. Gardelle
    CESTA, Le Barp
 
 

A simulation of the generation of Smith-Purcell (S-P) radiation at terahertz frequencies is performed using the two-dimensional particle-in-cell code MAGIC. The simulation supposes that a continuous, thin (but infinitely wide), mono-energetic electron beam passes over a diffraction grating, while a strong axial magnetic field constrains the electrons to essentially one-dimensional motion. We simulate two configurations, one similar to the Dartmouth S-P FEL [1], with a low energy continuous beam, and the other similar to the recent MIT experiment which uses a pre-bunched 15 MeV beam [2].

[1] A Bakhtyari, J. E. Walsh, and J. H. Brownell, Phys. Rev. Lett. E 65, 066503 (2002). [2] S. E. Korbly, A. S. Kesar, J. R. Sirigiri, and R. J. Temkin, Phys. Rev. Lett. 94, 054803 (2005)

 
   
TUPP009 Optimization Issues in a Harmonic Cascade FEL
 
  • G. De Ninno
    ELETTRA, Basovizza, Trieste
  • W.M. Fawley, G. Penn
    LBNL, Berkeley, California
  • W. Graves
    MIT, Middleton, Massachusetts
 
 

Funding: Work supported in part by the Office of Science, U.S. Dept. of Energy under Contract DE-AC03-76SF0098

Presently there is significant interest by multiple groups (e.g. BNL, ELETTRA, LBNL, BESSY, MIT) to reach short output wavelengths via a harmonic cascade FEL using an external seed laser. In a multistage device, there are a number of "free" parameters such as the nominal power of the input seed, the lengths of the individual modulator and radiator undulators, the strengths (i.e. the R56's) of the dispersive sections, the choice of the actual harmonic numbers to reach a given wavelength, etc., whose optimization is a non-trivial exercise. In particular, one can choose whether to operate predominantly in the "high gain" regime such as was proposed by Yu [1] in which case each radiator undulator is many gain lengths long or, alternatively, in the "low gain" regime in which case all undulators (except possibly the last radiator) are a couple gain lengths or less long and the output from each radiator essentially corresponds to coherent spontaneous emission from a pre-bunched beam. With particular emphasis upon the proposed two-stage FEL device for FERMI@Elettra, we discuss strategies for determining optimal cascade layouts based upon both analysis and numerical simulation results.

[1] L.H. Yu, Phys. Rev. A, 44, 5178 (1991).

 
   
TUPP010 Single Pass Free Electron Laser: The Reduced Hamiltonian
 
  • A. Antoniazzi, D. Fanelli, A. Guarino, S. Ruffo
    Universita di Firenze, Florence
  • G. De Ninno
    ELETTRA, Basovizza, Trieste
 
 

We discuss the analogies between two classical models of the single-pass free electron laser dynamics and of the beam-wave plasma instability. Moreover, a formal bridge between the two areas of investigation is established. This connection is here exploited to derive a reduced Hamiltonian formulation for the saturated regime of the free electron laser.A self consistent formulation of the parameters involved is proposed .

 
   
TUPP011 Multiple Time Scale Theory of Single-Pass Steady-State
 
  • A. Antoniazzi, D. Fanelli, S. Ruffo
    Universita di Firenze, Florence
  • J. Barre'
    LANL, Los Alamos, New Mexico
  • T. Dauxois
    ENS LYON, Lyon
  • G. De Ninno
    ELETTRA, Basovizza, Trieste
  • Y. Elskens
    Universite de Provence, Marseille
 
 

The non-linear dynamics of a single-pass, high-gain free-electron laser is analytically studied in the framework of the Vlasov-wave picture. A multiple time scale calculation is performed to derive the well known non-linear Landau equation for the complex amplitude of the unstable mode, which hence exhibits a limit cycle behaviour. The coefficients of the equation are analytically determined as function of a generic initial electron-beam distribution. Numerical results are presented. Possible extensions of this approach to the case of the Harmonic Generation are also discussed.

 
   
TUPP012 Control Chaotic Diffusion in a Single Pass Free Electron Laser
 
  • A. Antoniazzi, D. Fanelli
    Universita di Firenze, Florence
  • R. Bachelard, C. Chandre, M. Vittot
    CNRS/CPT, Marseille
 
 

We apply an innovative strategy to control chaotic diffusion in conservative systems to the case of a single pass Free Electron Laser. The core of our approach is a small apt modification of the system which channels chaos by building barriers to diffusion. By confining the electrons in phase space and limiting the oscillations of the dense core, we aim at stabilizing the laser intensity. Calculations are perfomed within the framework of a simplified Hamiltonian picture. Further extensions and future experimental applications are also discussed.

 
   
TUPP013 Spectral Properties of Planar Bi-Harmonic Undulators and Their Use for FEL Operation
 
  • F. Ciocci, G. Dattoli, L. Giannessi
    ENEA C.R. Frascati, Frascati (Roma)
  • S. Biedron, S.V. Milton
    ANL, Argonne, Illinois
  • H. Freund
    SAIC, McLean
 
 

We study the spectral details of planar bi-harmonic undulators and show that they have quite interesting properties. They can indeed be exploited to enhance or suppress harmonics and can be exploited in high gain segmented FEL devices to make more efficient the mechanisms of harmonic generation. We also show that the formalism we develop can be extended to the multi-component case and can usefully be exploited to study undulator magnetization errors.

 
   
TUPP014 Coherent Synchrotron Radiation: A Simulation Code Based on the Non-Linear Extension of the Operator Splitting Method
 
  • G. Dattoli
    ENEA C.R. Frascati, Frascati (Roma)
  • M.  Migliorati, A. Schiavi
    Rome University La Sapienza, Roma
 
 

The coherent synchrotron radiation (CSR) is one of the main problems limiting the performance of high intensity electron accelerators. A code devoted to the analysis of this type of problems should be fast and reliable: conditions that are usually hardly achieved at the same time. In the past, codes based on Lie algebraic techniques have been very efficient to treat transport problem in accelerators. The extension of these method to the non-linear case is ideally suited to treat CSR instability problems. We report on the development of a numerical code, based on the solution of the Vlasov equation, with the inclusion of non-linear contribution due to wake field effects. The proposed solution method exploits an algebraic technique, using exponential operators implemented numerically in C++. We show that the integration procedure is capable of reproducing the onset of an instability and effects associated with bunching mechanisms leading to the growth of the instability itself. In addition, parametric studies are presented on the dependence of the effects on the e-beam energy spread and bunch length, considerations on the threshold of the instability are also developed, and future improvements of the work are presented.

 
   
TUPP015 Theory of Cerenkov Free Electron Lasers
 
  • G. Dattoli
    ENEA C.R. Frascati, Frascati (Roma)
  • V.B. Asgegar
    University of Pune, Pune
 
 

In this paper we show that Cerenkov Free Electron Laser oscillators can be studied using a treatment closely similar to that of the magnetic undulator counterpart. We prove that the saturation dynamics can be modeled by strictly similar formulae and that also for Cerenkov Free Electron Laser the saturation intensity is a quantity of paramount importance. We consider hybrid (undulator and cerenkov) FEL devices and show how they can be exploited to assist the non linear higher order harmonic generation.

 
   
TUPP017 Backward Wave Excitation and Generation of Oscillations in Free-Electron Lasers in the Absence of Feedback: Beyond the High Gain Approximation 266
 
  • Y. Pinhasi, Yu. Lurie, G.A. Pinhasi, A. Yahalom
    CJS, Ariel
 
 

Microwave tubes and free-electron lasers are based on distributed interaction between electromagnetic radiation and gain media. When such devices are operating in an amplifier configuration, a forward wave is amplified while propagating in a polarized medium, in a stimulated emission process. Formulating a coupled mode theory for excitation of both forward and backward waves in a distributed gain medium, we have identified in previous works [1] conditions leading to efficient excitation of backward wave without any mechanism of feedback or resonator assembly. The induced polarization is given in terms of an electronic susceptibility tensor, resulting in a coupling coefficient betweens the waves. In this work we extend our previous results in two directions: 1. We discuss the case of a complex coupling coefficient between the backward and forward waves and extend our previous results with respect to a real coupling coefficient, thus the present work discusses a more general and realistic case. 2. We discuss the solution of the same problem relaxing the "high gain" assumption. This leads to a more complex set of third order differential equations.

[1] "Backward Wave Excitation and Generation of Oscillations in Distributed Gain Media and Free-Electron Lasers in the Absence Of Feedback" the 26th International FEL Conference, Trieste, Italy.

 
   
TUPP018 Variational Approach for Coupled Backward and Forward Wave Excitation in Free-Electron Lasers 270
 
  • A. Yahalom, Yu. Lurie, Y. Pinhasi
    CJS, Ariel
 
 

In a recent paper [1] we have described a novel variational formulation for the propagation and generation of radiation in wave-guides. The formulation is based on the representation of all the involved quantities in the frequency domain and the decomposition of field and currents in terms of the wave-guide transversal Eigen function. In this work we present the utilization of this formalism to the derivation of a numerical scheme that is used to study the build up of radiation in free electron lasers in the linear approximation.

[1] Asher Yahalom, Yosef Pinhasi & Yuri Lurie "Spectral and Variational Principles of Electromagnetic Field Excitation in Wave Guides" submitted to Physics Letters A (2004).

 
   
TUPP019 Fully Relativistic Free-Electron Laser in a Partially Filled Waveguide
 
  • B. Farokhi
    IPM, Tehran
 
 

A linear theory for a fully relativistic free electron laser with a one dimensional helical wiggler and axial magnetic field in the collective regime is presented. The configuration consists of a cylindrical waveguide with arbitrary ratio of electron beam radius to waveguide inner radius . Transverse and longitudinal components of the velocity are treated as relativistic. Parametric decay of the wiggler pump wave, in the beam frame, in to a relativistic space-charge wave and a relativistic electric-magnetic waveguide mode is analyzed in three dimensions. A relativistic non-linear wave equation is derived in a form which includes the coupling of and modes and employed to obtain a formula for the spatial growth rate of the excited eigenmodes. It was found that the relativistic treatment of the electron oscillations in the wiggler field destroys the cyclotron resonance which appears in the nonrelativistic case. Nevertheless, appreciable amplification was found. Numerical analysis is conducted to study the growth rate, radiation wavelength, and required relativistic factor as a function of axial magnetic field and radius ratio .

 
   
TUPP020 Self-Field in Free-Electron Laser with Planar Wiggler and Ion Channel Guiding
 
  • B. Farokhi
    IPM, Tehran
 
 

A theory of ion-channel guiding in a planar wiggler is presented. The self-electric and self magnetic fields of a relativistic electron beam passing through a wiggler and ion-channel are analyzed. A numerical study shows that for Lorentz factor and the self-fields can produce very large effects. Also, we have followed the self-consistent method for the analysis of self-magnetic field. The equilibrium orbits and their stability, under the influence of self-electric and self-magnetic fields, are analyzed. New unstable orbits, in the first part of the group I orbits and in the resonance region of the group II orbits are found.

 
   
TUPP021 An Analysis of Spontaneous Emission in Free-Electron Laser
 
  • Q.K. Jia
    USTC/NSRL, Hefei, Anhui
 
 

The formula of spontaneous emission in free-electron laser is derived from the one dimensional Maxwell equation in the time domain. The effective start-up noise power of Self-Amplified Spontaneous Emission (SASE) process is given, it includes the incoherent spontaneous emission contribution, which is equal to the spontaneous undulator radiation in the first power gain length, and it also includes the coherent spontaneous emission contribution. The short pulse case is analysed.

 
   
TUPP022 CSR Effects in a Bunch Compressor: Influence of the Beam Frame Transverse Force
 
  • G. Bassi, J.A. Ellison
    UNM, Albuquerque, New Mexico
 
 

Funding: Support from DOE grants DE-AC02-76SF00515 and DE-FG02-99ER1104 is gratefully acknowledged.

We study the influence of coherent synchrotron radiation (CSR) on particle bunches traveling on arbitrary planar orbits between parallel conducting plates (shielding) with a Vlasov approach. [1] The fields excited by the bunch are computed in the lab frame using a formula simpler than that based on retarded potentials. The Vlasov equation is solved in the beam frame interaction picture. In recent numerical investigations we solved the Vlasov equation for a bunch compressor using the Liouville-Maxwell approximation (LMA), where the bunch density is evolved under the fields produced by the unperturbed density (subject to external fields only), neglecting the beam frame transverse force. [2] Here we report on the influence of the beam frame transverse force on the equations of motion.

[1] "Vlasov Treatment of Coherent Synchrotron Radiation from Arbitrary Planar Orbits" ,to be published in the Proceedings of ICAP04, St. Petersburg, R. Warnock, G. Bassi and J. A. Ellison. [2] "Progress On a Vlasov Treatment of Coherent Synchrotron Radiation from Arbitrary Planar Orbits" ,Proceedings of PAC2005, Knoxville, G. Bassi, J. A. Ellison and R. Warnock.

 
   
TUPP023 CRM in the Regime of Nonresonant Bunching
 
  • I.V. Bandurkin, V.L. Bratman, A.V. Savilov
    IAP/RAS, Nizhny Novgorod
 
 

Funding: This work is supported by the Russian Foundation for Basic Research, project 05-02-16852.

New regime of electron-wave coupling in cyclotron resonance maser (CRM) is proposed. In this regime, during the most part of interaction process electrons move in the field of rf wave which is relatively far from cyclotron resonance. It is shown, that if resonance mismatch is chosen properly, an effective bunching takes place, an amplitude of forming rf current weakly depending on the velocity spread. Simulations show that, whereas the efficiency of traditional regimes quickly decreases with increasing velocity spread, efficiency of the proposed scheme practically does not change and for relative value of spread in transverse velocities of 40% is twice as large as corresponding efficiency of the conventional regimes. The regime seems to be also prospective for realization of CRM with frequency multiplication. In such a scheme, resonance mismatch for low-frequency wave in bunching section should be such that high-frequency wave be in resonance with the beam. Thus, the device operates like the single-frequency oscillator in the regime of nonresonant bunching at the low frequency, and the high-frequency wave is excited by the high harmonic of electron current inside the bunching section.

 
   
TUPP025 Classic Theory of Red Shifting in Radiation of an Electron in the Field of Plane Linear Polarized Electromagnetic Wave
 
  • A.Y. Zelinsky, I.V. Drebot, Yu.N. Grigor'ev, O.D. Zvonarjova
    NSC/KIPT, Kharkov
 
 

An expression for electron radiation frequency in the field of plane linear polarized electromagnetic wave was derived with classical electrodynamics approach. It is shown that scattered radiation of an initially rest electron is different in frequency from an incident electromagnetic wave. Using Bohr correspondence principle and supposing uniform distribution function of electrons on phase of incident wave the Compton formula for "red shifting" of scattered radiation frequency was obtained. The correspondence principle allowed to express the value of Planck constant through parameters of the incident wave and the interacting electron. It is shown in the paper that Bohr correspondence principle can be applied for the case of small number of photons in an oscillation mode.

 
   
TUPP026 Numerical Simulation Studies of Smith-Purcell Free-Electron Lasers 274
 
  • V. Kumar, K.-J. Kim
    ANL, Argonne, Illinois
 
 

Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences, under contract No. W-31-109-ENG-38

We present a one-dimensional time-dependent analysis and simulation of Smith-Purcell (SP) free-electron lasers (FELs). The coupled Maxwell-Lorentz equations for SP-FELs are set up, and the details of numerical simulation are presented. For an SP-FEL based on low energy (~35 keV) DC (~1 mA) electron beam from a scanning electron microscope, we show that around 100 mW of power can be generated at THz. frequency in the form of a surface electromagnetic wave due to FEL interaction. We propose a two-grating configuration where the electron beam gets bunched in the first grating and radiates copiously in the second grating due to coherent spontaneous emission, if the parameters of the second grating are optimized suitably.

 
   
TUPP027 Time-Dependent Simulation of Free-Electron Laser Amplifiers and Oscillators 278
 
  • H. Freund
    SAIC, McLean
 
 

Funding: Work supported by ONR, NAVSEA, and the JTO

Time-dependent FEL simulations use a variety of techniques. Most simulations use a slowly varying envelope approximation (SVEA). One such technique assumes that the envelope varies only in z combined with a field representation as an ensemble of discrete harmonics, which is equivalent to a time-dependent simulation [1] but is computationally prohibitive. A second technique uses an SVEA in both in z and t [2]. The particles and fields are advanced in z using the same process as in steady-state simulations and then the time derivative describing slippage is applied. This is used in wiggler-averaged codes such as GINGER [3] and GENESIS [4]. We describe the inclusion of this technique in the non-wiggler-averaged code MEDUSA [5], which is applied to amplifiers and oscillators. MEDUSA differs from GINGER and GENESIS also in the way the field is treated. GINGER and GENESIS use a field solver and must explicitly propagate the field outside the wiggler oscillators. This is computationally intensive. MEDUSA uses a Gaussian mode ensemble; hence, there is no need to propagate the fields outside the wiggler, and MEDUSA is able to simulate FEL oscillators in 3-D using relatively modest computational resources.

[1] N. Piovella, Phys. Plasmas 6, 3358 (1999). [2] R. Bonifacio et al., Phys. Rev. A 40, 4467 (1989). [3] W. Fawley, LBID-2141, CBP Tech Note-104, UC-414, 1995. [4] S. Reiche, NIMA 429, 243 (1999). [5] H.P. Freund et al., IEEE JQE 36, 275 (2000).

 
   
TUPP028 Spectral-Angular Characteristics of the LCLS in the Near and Far Fields 282
 
  • R. Tatchyn
    SLAC, Menlo Park, California
 
 

The unusually long insertion devices being prepared for Angstrom-wavelength Free Electron Lassers (FELs) will generate spectral-angular distributions in the proposed experimental areas substantially different from those conventionally calculated for the far field. In this paper we report on computational simulations of near vs. far field distributions for the SLAC linac Coherent Light Source (LCLS) undulator, an insertion device approximateely 140 meters long. The properties of the coherent radiation as a limiting case of the near-field emission, for the special condition of a microbunched beam radiating along the undulator axis, are reviewed.

 
   
TUPP029 Weak-Field Gain in Short-Rayleigh Length Free Electron Lasers
 
  • J. Blau, W.B. Colson, S.P. Niles, R. Vigil
    NPS, Monterey, California
 
 

Funding: JTO, ONR, NAVSEA

A compact, high-power free electron laser may require a short-Rayleigh length resonator to reduce the power intensity on the mirrors. Conventional FEL theory predicts that as the Rayleigh length is reduced below an optimum value of approximately one-third of the undulator length, the filling factor and hence the gain will be reduced. However, this theory is only valid for extremely low gains (~1%); for modest gains (~20%), the optical mode is distorted and the amplification is enhanced. Simulations show that the weak-field gain remains fairly constant as the Rayleigh length is reduced.

 
   
TUPP030 Optical Beam Properties and Performance of the MID-IR FEL at ELBE 286
 
  • U. Lehnert, P. Michel, W. Seidel, D. Stehr, J. Teichert, D. Wohlfarth, R. Wuensch
    FZR, Dresden
 
 

First lasing of the mid-infrared free-electron laser at ELBE was achieved on May 7, 2004. Since then stable lasing has been achieved in the IR range from 4 to 22~μm using electron beam energies from 15 to 35~MeV. At all wavelengths below 20~μm a cw optical power higher than 1~W can be produced with an electron beam of 50~pC bunch charge or less. The optical pulse width at its minimum (2.2~ps measured at 17~μm) resembles the typical electron bunch length of 2~ps without bunch compression but can be increased by detuning the optical cavity. The optical bandwidth was in all cases close to the fourier limit.

 
   
TUPP031 A Far-Infrared FEL for the Radiation Source ELBE 290
 
  • W. Seidel, E. Grosse, U. Lehnert, P. Michel, R. Schlenk, U. Willkommen, D. Wohlfarth, R. Wuensch
    FZR, Dresden
  • A. Wolf
    MPI-K, Heidelberg
 
 

After successfully commissioning the mid-infrared FEL (U27) and adjoining a second accelerator unit (up to 35 MeV) at ELBE we have modified our plan how to produce radiation in the far infrared.To ensure the continuous variation of the wavelength up to 150 microns we want to complement the U27 undulator by a permanent magnet undulator with a period of 100 mm (U100). The minimum gap of 24 mm and the hybrid construction consisting of Sm/Co magnets and soft iron poles ensures sufficient radiation resistance and allows rms undulator parameters up to 2.7. The large field variation allows us to cover the whole wavelength range by only two different electron energies (e.g. 20 and 35 MeV). To reduce the transverse beam size we use a partial waveguide which is 10 mm high and wide enough to allow free propagation in horizontal direction. It spans from the last quadrupole in front of the undulator up to the downstream mirror and is somewhat longer than 8 m. To minimize the coupling losses between free propagation and the waveguide mode appropriate bifocal resonator mirrors will be used. Detailed calculations and computer simulations predict an outcoupled laser power of roughly 35 W around 40 microns and 20 W at 150 microns.

 
   
TUPP032 Compact THz FELs and Their Potential in Biological Applications
 
  • G.P. Gallerano, A. Doria, E. Giovenale, G. Messina, I.P. Spassovsky
    ENEA C.R. Frascati, Frascati (Roma)
 
 

Two THz FEL sources are available at ENEA-Frascati covering the spectral range from 90 GHz to 0.7 THz. The first source, the ENEA Compact FEL, is based on a 5 MeV Microtron providing 4 A of peak current in 13 ps bunches. Peak power in excess of 3kW is obtained at 130 GHz. When the beam is focused, a peak E-field greater than 2 kV/cm can be obtained in the micropulse. The second source, FEL-CATS, is based on a 2.5 MeV RF Linac. After the Linac electrons enter a RF device that correlates their distribution in energy and phase. As a result a strong coherent spontaneous emission occurs in the undulator. Power up to several kW has been measured in the macropulse. The absence of a resonator results in a broad band emission from 0.4 to 0.7 THz. The peculiar temporal structure of the emitted radiation allows the investigation of the effects of high peak power, while maintaining a low average power incident on the sample. A variety of biological systems have been studied with the ENEA Compact FEL in the frame of the European project THz-BRIDGE. More recently a reflective THz imaging setup has been developed and devoted to the study of hydric stress conditions in living plants.

One of the authors, I.P. Spassovsky, acknowdleges support from an ENEA-ICTP fellowship

 
   
TUPP033 STATISTICAL STUDY OF SPONTANEOUS EMISSION IN THE ISRAELI ELECTROSTATIC ACCELERATOR FREE-ELECTRON LASER 293
 
  • A. Yahalom, Yu. Lurie, Y. Pinhasi
    CJS, Ariel
  • A. Eliran, A. Gover
    University of Tel-Aviv, Faculty of Engineering, Tel-Aviv
 
 

We have measured spontaneous FEL radiation in the Israeli Electrostatic Accelerator FEL (EA-FEL) . The measurements were repeated numerous times in order to get information of statistical significance. The distribution of the radiation power measurements and various statistical moments derived from this distribution contain information on the electron beam statistics and its interaction with the wiggler magnetic field and the resonator that contain the radiation. In this work we present both the measured radiation power statistical data and its connection to the statistics of the electron beam through numerical and analytical models.

 
   
TUPP034 The Israeli EA-FEL Upgrade Towards Long Pulse Operation for Ultra-High Resolution Single Pulse Coherent Spectroscopy 297
 
  • A. Gover, A. Faingersh, M. Kanter, B. Kapilevich, B. Litvak, S. Peleg, Y. Socol, M. Volshonok
    University of Tel-Aviv, Faculty of Engineering, Tel-Aviv
  • M. Einat, Yu. Lurie, Y. Pinhasi, A. Yahalom
    CJS, Ariel
 
 

The Israeli Electrostatic Accelerator FEL (EA-FEL) is now being upgraded towards long pulse (1005s) operation and ultra-high resolution (10(-6)) single pulse coherent spectroscopy. We present quantitative estimations regarding the applications of controlled radiation chirp for spectroscopic applications with pulse-time Fourier Transform limited spectral resolution. Additionally, we describe a novel extraction-efficiency-improving scheme based on increase of accelerating voltage (boosting) after saturation is achieved. The efficiency of the proposed scheme is confirmed by theoretical and numerical calculations. The latter are performed using software, based on 3D space-frequency domain model. The presentation provides an overview of the upgrade status: the high-voltage terminal is being reconfigured to accept the accelerating voltage boost system; a new broad band low-loss resonator is being manufactured; multi-stage depressed collector is assembled.

 
   
TUPP035 Generation of Coherent Synchrotron Radiation from JAERI-ERL 301
 
  • R. Hajima, H. Iijima, N. Kikuzawa, E.J. Minehara, R. Nagai, T. Nishitani, M. Sawamura
    JAEA/FEL, Ibaraki-ken
  • S. Okuda
    Osaka Prefecture University, Sakai
  • T. Takahashi
    KURRI, Osaka
 
 

An electron beam with high-average current and short bunch length can be accelerated by energy-recovery linac. Coherent synchrotron radiation (CSR) from such an electron beam will be a useful light source around millimeter wavelength. We report results from a preliminary measurement of CSR emitted from a bending magnet of JAERI-ERL. Possible enhancement of CSR power by FEL micro-bunching is also discussed.

 
   
TUPP036 Status and Future Plans of JAERI Eergy-Recovery Linac FEL
 
  • R. Hajima, H. Iijima, N. Kikuzawa, E.J. Minehara, R. Nagai, N. Nishimori, T. Nishitani, M. Sawamura, T. Yamauchi
    JAEA/FEL, Ibaraki-ken
 
 

An energy-recovery linac for a high-power free-electron laser is in operation at Japan Atomic Energy Research Institute (JAERI). In this paper, we report results of research activities and future plans of JAERI ERL-FEL, which are the construction of FEL transport line, the operation of newly-installed RF controller and IOTs, the development of super-lattice photo cathode.

 
   
TUPP037 JAERI 10kW High Power ERL-FEL and Its Applications in Nuclear Energy Industries 305
 
  • E.J. Minehara, R. Hajima, H. Iijima, N. Kikuzawa, R. Nagai, N. Nishimori, T. Nishitani, M. Sawamura, T. Yamauchi
    JAEA/FEL, Ibaraki-ken
 
 

The JAERI high power ERL-FEL has been extended to the more powerful and efficient free-electron laser (FEL) than 10kW for nuclear energy industries, and other heavy industries like defense, shipbuilding, chemical industries, environmental sciences, space-debris, and power beaming and so on. In order to realize such a tunable, highly-efficient, high average power, high peak power and ultra-short pulse FEL, we need the efficient and powerful FEL driven by the JAERI compact, stand-alone and zero boil-off super-conducting RF linac with an energy-recovery geometry. Our discussions on the ERL-FEL will cover the current status of the 10kW upgrading and its applications of non-thermal peeling, cutting, and drilling to decommission the nuclear power plants, and to demonstrate successfully the proof of principle prevention of cold-worked stress-corrosion cracking failures in nuclear power reactors under routine operation using small cubic low-Carbon stainless steel samples.

 
   
TUPP038 Particle in Cell Simulation on Grating Radiation 309
 
  • D. Li, K. Imasaki
    ILT, Suita, Osaka
  • G.S. Park, Y. Yang
    SNU, Seoul
 
 

A renewed interest of Smith-Purcell system has been raised since J. Urata et.al observed a possible exponential gain in their experiment using electron microscope beam. Several theories were presented to calculate the exponential gain. We analyzed this problem in the way of particle in cell simulation, which provides many details in understanding the physics of the radiation from a grating.

 
   
TUPP039 Mode Dynamics in the Bragg FEL Based on Coupling of Propagating and Trapped Waves
 
  • N.S. Ginzburg, A.M. Malkin, N.Yu. Peskov, R.M. Rozental, A. Sergeev, V.Yu. Zaslavsky
    IAP/RAS, Nizhny Novgorod
 
 

A novel Bragg FEL scheme is discussed in which an electron beam synchronously interacts with a propagating wave, and the latter is coupled to a quasi cut-off mode. This coupling is realized by either helical or asimuthally symmetric corrugation of the waveguide walls. The quasi cut-off mode provides feedback in the system leading to self-excitation of the whole system while the efficiency in steady-state regime of generation is almost completely determined by the propagating mode, synchronous to the beam. Analysis based on averaged time domain approach as well as on direct PIC code simulation shows that the efficiency of such a device in the single mode single frequency regime can be rather high. The main advantage of the novel Bragg resonator is provision of higher selectivity over transverse index than traditional scheme of Bragg FEL. The cold microwave testing of the Bragg structure based on coupling of propagating and trapped waves in the Ka band demonstrated a good agreement with theoretical considerations. The novel feedback scheme should be used on a JINR- IAP FEL as a method of increasing the operating frequency for fixed transverse size of interaction space.

 
   
TUPP040 Predicted Parameters of the Second Stage of High Power Novosibirsk FEL
 
  • A.V. Kuzmin, O.A. Shevchenko, N. Vinokurov
    BINP SB RAS, Novosibirsk
 
 

The first stage of Novosibirsk high power terahertz FEL was successfully put into operation in 2003 [1]. The measured parameters of the FEL turned out to be in a good agreement with calculations [2]. The second and the third stages of the FEL are under construction now. The beam energy at the second stage will be about 20 MeV and the wavelength will change in the range 40-80 μm. In this paper we present the design parameters for the second stage FEL. The simulations were carried out with the help of 1-D code based on macroparticles. This code was previously used for the first stage simulations [2].

[1] Antokhin E.A. et al. NIM A528 (2004) p.15-18. [2] Kuzmin A.V., Shevchenko O.A., Vinokurov N.A. NIM A543 (2005) p.114-117.

 
   
TUPP041 Simulations of the Jefferson Lab FEL Using the New Electromagnetic Wiggler 313
 
  • J. Blau, O.E. Bowlin, W.B. Colson, R. Vigil, T. Voughs, B.W. Williams
    NPS, Monterey, California
 
 

Funding: JTO, ONR, NAVSEA

After successfully lasing at 10 kW of average power at a wavelength of 6 μm, a new electromagnetic wiggler has been installed at Jefferson Lab, which will be used to achieve high power at shorter wavelengths. Wavefront propagation simulations are used to predict system performance for weak-field gain and steady-state extraction, as the bunch charge, pulse length, electron beam radius, Rayleigh length, and mirror output coupling are varied.

 
   
TUPP042 High Power CW Operation of a Hole-Outcoupled Free-Electron Laser
 
  • M.D. Shinn, C.P. Behre, S.V. Benson, C.W. Gould, J.G. Gubeli, D. Hardy, G. Neil, S. Zhang
    Jefferson Lab, Newport News, Virginia
 
 

Funding: This work supported by the Office of Naval Research, the Joint Technology Office, the Army Night Vision Laboratory, the Air Force Research Laboratory, the Commonwealth of Virginia, and by DOE Contract DE-AC05-84ER40150.

In order to provide widely-tunable light to our users, we used a hole outcoupler. To date, we've produced 85 W at 2.8 microns, and been able to continuously tune over a 1 micron spectral range. Besides the anticipated low outcoupling efficiency associated with this scheme, we found that we had considerable problems stabilizing the output when we operated our FEL in cw mode. We believe that this is due to the long time available for mode competition to develop. Measurements of gain, loss, and transverse mode profiles (both intracavity and output) will be compared with our models.

 
   
TUPP043 Vacuum Window Design for High-Power Lasers 317
 
  • T.V. Shaftan
    BNL, Upton, Long Island, New York
 
 

Funding: The manuscript has been authored by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH1-886 with the U.S. Department of Energy.

One of the problems in the high-power lasers design is in outcoupling of a powerful laser beam out of a vacuum volume into atmosphere. Usually the laser device is located inside a vacuum tank. The laser radiation is transported to the outside world through the transparent vacuum window. While considered transparent, some of the light passing through the glass is absorbed and converted to heat. For most applications, these properties are academic curiosities; however, in multi-kilowatt lasers, the heat becomes significant and can lead to a failure. The absorbed power can result in thermal stress, reduction of light transmission and, consequently, window damage. Modern optical technology has developed different types of glass (Silica, BK7, diamond, etc.) that have high thermal conductivity and damage threshold. However, for kilo- and megawatt lasers the issue still remains open. In this paper we present a solution that may relieve the heat load on the output window. We discuss advantages and issues of this particular window design.

 
   
TUPP044 Short Rayleigh Range Free Electron Laser Amplifiers
 
  • L.-H. Yu, D.F.L. Liu, J.B. Murphy, J. Rose, T.V. Shaftan, X.J. Wang, T. Watanabe
    BNL, Upton, Long Island, New York
 
 

An important requirement for a high average power laser system is a manageable power density on the first optical element. One possibility to achieve this is a single pass amplifier which generates a short Rayleigh range (SRL) light beam. We present design parameters and calculated performances for several SRL configurations. These include a simulation of the optically guided (pinched) MW class FEL [1], the scalloped beam FEL amplifier [2] and high gain TOK amplifiers we propose to explore at our SDL facility.

[1] P. Sprangle et al. , IEEE J. of Quantum Electronics, Vol. 40, No. 12, 1739, 2004 [2] D. Nguyen, private communication, 2005.

 
   
TUPP046 Design Study of a Compact Megawatt Class FEL Amplifier Based on the VISA Undulator 320
 
  • T. Watanabe, D.F.L. Liu, J.B. Murphy, I.P. Pinayev, J. Rose, T.V. Shaftan, J. Skaritka, T. Tanabe, T. Tsang, X.J. Wang, L.-H. Yu
    BNL, Upton, Long Island, New York
  • S. Reiche
    UCLA, Los Angeles, California
  • P. Sprangle
    NRL, Washington, DC
 
 

The design of a Short Rayleigh Length (SRL) FEL amplifier based on the strong focusing VISA undulator [1] is presented in this study. The SRL FEL amplifier will be operating in the IR (0.8 - 1 μm), and consists of a two-meter VISA undulator with a peak seed laser power of about 1 kW. The FEL power and transverse mode evolution along the undulator were investigated using the three-dimensional numerical code GENESIS1.3. The evolution of the FEL output from the undulator exit to the first downstream optics is also studied. The possibility of using the proposed amplifier for a two-stage cascaded HGHG FEL [2] at the BNL SDL is also explored. The design parameters and the numerical results will be presented.

[1] R. Carr et al., PRSTAB, Vol. 4, 122402 (2001). [2] J. Wuard and L.H. Yu, NIMA 475, 104 (2001).

 
   
TUPP047 Gamma Laser on the Base of Intense Relativistic Electron Beam and Oriented Single Crystal
 
  • A.O. Aganyants
    YerPhI, Yerevan
 
 

Experimental investigations of gamma ray emission at passage 4.3 GeV electron beam through the crystal have shown that yield of radiation grows non-linearly versus the electron beam intensity both in extremely low-energy coherent part of spectrum (coherent gamma rays) and even in more high energy range of one. It is observed a transition to saturation mode of the radiation even if to change some parameters of a crystal target. Apparently, the exciting of atomic medium of the crystal by intense electron beam results in process of self-organization or phasing of atoms that strengthens photon emission of relativistic electrons.

 
   
TUPP048 A Two-Frequency RF Cavity for the PSI Low Emittance Gun 324
 
  • J.-Y. Raguin, R.J. Bakker, K.S.B. Li, M. Pedrozzi
    PSI, Villigen
 
 

In the Low Emittance Gun (LEG) under development at PSI an extremely bright electron beam is produced from a field emission array and then rapidly accelerated in a diode configuration up to 1 MeV with gradients of the order of 250 to 500 MV/m. The electronic emission from such a cold cathode allows normalized intrinsic emittance below 0.1 mm.mrad well suited for X-ray FELs or linear collider applications. The diode is followed by an L-band RF-gun like cavity to further accelerate the beam. A third harmonic field is superposed to the fundamental [1] 1.5 GHz pi-mode field to minimize the RF emittance. We report here on the design of such a two-frequency RF cavity with some details on the RF coupling and possible tuning mechanisms. Beam dynamics studies, performed with PARMELA and the fully self-consistent code MAFIA, are presented and compared with the results obtained for an RF cavity excited with the fundamental frequency only.

[1] D.H. Dowell et al., Nucl. Instr. and Meth. A 528 (2004) 316.

 
   
TUPP049 Smith-Purcell Distributed Feedback Laser 328
 
  • D. Kipnis, E. Dyunin, A. Gover
    University of Tel-Aviv, Faculty of Engineering, Tel-Aviv
 
 

Smith-Purcell radiation is the emission of electromagnetic radiation by an electron beam passing next to an optical grating. Recently measurement of relatively intense power of such radiation was observed in the THz-regime [1]. To explain the high intensity and the super-linear dependence on current beyond a threshold it was suggested that the radiating device operated in the high gain regime, amplifying spontaneous emission (ASE) [1,2]. We contest this interpretation and suggest an alternative mechanism. According to our interpretation the device operates as a distributed feedback (DFB) laser oscillator, in which a forward going surface wave, excited by the beam on the grating surface, is coupled to a backward going surface wave by a second order Bragg reflection process. This feedback process produces a saturated oscillator. We present theoretical analysis of the proposed process, which fits the reported experimental results, and enables better design of the radiation device, operating as a Smith-Purcell DFB laser.

[1] A.Bakhtyari, J.E.Walsh, J.H.Brownell, Phys.Rev. ·1065 006503 (2002). [2] H.L. Andrews, C.A. Brau, Phys.Rev. ST-AB 7, 070701 (2004).

 
   
TUPP050 Free Electron Laser Pulse Control by Acousto Optic Modulators 332
 
  • T. Kanai, K. Awazu, S. Yoshihashi-Suzuki
    Osaka University, Suita
 
 

Free Electron Laser (FEL) at Osaka University can be continuously varied in the range of 5.0-20.0 μm. A FEL has a double pulse structure. The structure consists of a train of macropulses of the pulse width 15 μs, and each macropulse contains a train of 330 micropulses of the pulse width 5 ps. The tunability and short pulse afford new medical applications such as investigation of protein dynamics and ablation of soft tissues. Precise control of micropulse train is very important for medical applications using FEL because macropulse with long pulse duration sometimes leads to undesirable thermal effects. FEL pulse control system using an acousto optic modulators (AOM) was developed in order to investigate of non-thermal effect between the FEL and tissue. This system provide a very good efficiency (~60 %) and a fast switching speed (>200 ns). A phosphorylated protein was irradiated with FEL that controlled the pulse. These result confirmed that the thermal effect is controlled by pulse duration. This system will be expected as a novel tool for investigation of interaction between the FEL and normal tissue.

 
   
TUPP051 Free-Electron Laser with Bessel Beam Cavity 336
 
  • D. Li
    ILT, Suita, Osaka
 
 

The conventional cavity for a free-electron laser (FEL) oscillator forms Gaussian optical beam, transversely spreading along the interaction region. The transverse divergence will induce reduction of the FEL gain by three aspects: degenerating filling factor, causing diffraction loss and limiting the effective interaction distance. Bessel optical beam has been experimentally demonstrated diffraction-free characteristic, providing a possibility of improvement of FEL gain. In this paper, we present a conceptual design of a Bessel beam cavity for the free-electron laser. This cavity generates nondiffracting optical beam in the wiggler, which can improve the filling factor, decrease the diffraction loss and elongate the effective interaction distance.

 
   
TUPP052 Compact, Ultra-Bright Coherent Transition Radiation Terahertz Source
 
  • O.J. Luiten, M.J. Van der Wiel
    TUE, Eindhoven
 
 

Funding: Foundation for Fundamental Research on Matter (FOM), The Netherlands

We are developing a compact terahertz source based on the coherent emission of transition radiation by ultra-short electron bunches (typically 100 pC in 100 fs) of moderate energy (typically 5 MeV) passing through a foil. Such electron bunches can be realized by velocity bunching of uniform ellipsoidal "waterbag" electron bunches, which can be created by photoemission with properly shaped femtosecond laser pulses [1]. Calculations indicate that a significant part of the kinetic energy of the bunch is converted into a huge coherent burst of terahertz radiation.

[1] O.J. Luiten, S.B. van der Geer, M.J. de Loos, F.B. Kiewiet, and M.J. van der Wiel, Phys. Rev. Lett. 93, 094802 (2004).

 
   
TUPP053 Novel Techniques using FEM for Material Production and Processing 339
 
  • A.I. Al-Shamma'a, J. Lucas, A. Shaw, R.A. Stuart, C.C. Wright, M. houghton
    University of Liverpool, Liverpool
  • J. hamelin
    ,
 
 

The objectives of this European project are to use high frequency microwave technology to develop focussed energy sources for industrial applications. The microwaves, generated in the 10GHz to 20GHz frequency range by using a table top FEM has been used to investigate novel solutions for material processing and material production, including microwave heating of substrates, microwave chemistry for increasing the speed of thermal reactions, microwave plasma chemistry for aiding gaseous reactions in the reduction of combustion pollutants and the production of UV/ozone for germicidal activities. In this paper we report unique results and analysis in using tuneable FEM system compared with the conventional magnetron 2.45 GHz system.

 
   
TUPP054 Ultrafast Coherent Control and Characterization of Surface Reactions using FELs 343
 
  • H. Ogasawara, D. Nordlund
    SLAC, Menlo Park, California
  • A. Nilsson
    New Affiliation Request Pending, Menlo Park, California
 
 

The microscopic understanding of surface chemistry requires a detailed understanding of the dynamics of elementary processes at surfaces. The ultrashort electron pulse obtained in the linear accelerator to feed the FEL can be used for generation of coherent synchrotron radiation in the low energy THz regime. With the current parameters for LCLS this corresponds to radiation with energy corresponding to excitations of low-energy vibrational modes of molecules on surfaces or phonons in substrates. The coherent radiation can coherently manipulate atoms or molecules on surfaces. In this respect a chemical reaction can be initiated by coherent atomic motion along a specific reaction coordinate. Since the THz radiation is generated from the same source as the FEL radiation full-time synchronization for pump-probe experiments will be possible. The possibility to perform time-resolved X-ray Emission Spectroscopy (XES) and X-ray Photoelectron Spectroscopy (XPS) measurements as a probe of chemical dynamics is an exciting prospect. The combination of THz and soft x-ray spectroscopy could be a unique possibility for low repetition FEL facilities for ultrafast surface chemistry studies.

 
   
TUPP055 Ultra-Fast Pump-Probe Detection using Plasmas
 
  • R. Tatchyn
    SLAC, Menlo Park, California
 
 

The temporal resolution of pump-flash interactions in the ultrashort (fs-as) regime is limited by the characteristic time constants of the excited states in the detector material. If the relaxation time constant is appreciably longer that the time interval between the pump and probe signals the response of the detector material to the probe represents a temporal convolution of the pump and probe responses, setting a lower limit on the resolution to which the interval between the two pulses can be measured. In most of the solid state ultrafast detection schemes that are being considered for the ultra-short pulse x-ray sources under current development at SLAC and elsewhere the characteristic time constants are related to the bound states of the atoms comprising the material or to the relaxation times of phase transitions or charge carrier populations of the lattice, setting a probable lower limit on the attainable resolution on the order of ~0.1 ps. In this paper we consider a novel detection principle predicated on the excitation of specially prepared unbound states in an ionized plasma and estimate its potential for extending the lower limit of resolution into the as regime.

 
   
TUPP056 Harmonic Inverse FEL Interaction at 800nm
 
  • C.M.S. Sears, E.R. Colby, R. Siemann, J.E. Spencer
    SLAC, Menlo Park, California
  • R.L. Byer, T. Plettner
    Stanford University, Stanford, Califormia
 
 

The inverse Free Electron Laser (IFEL) interaction has recently been proposed and demonstrated as a premodulator for High Gain Harmonic Generation (HGHG) experiments. These experiments utilized the fundamental of the interaction between the laser field and electron bunch. In the current experiment, we explore the higher order resonances of the IFEL interaction from a 3 period, 1.8 centimeter wavelength undulator with a picosecond, 0.25 mJ/pulse laser at 800nm. The resonances are observed by adjusting the gap of the undulator while keeping the beam energy constant. The harmonic IFEL can add flexibility to HGHG FEL design.

 
   
TUPP057 Free Electron Lasers in 2005 347
 
  • W.B. Colson, R. Vigil, T. Voughs
    NPS, Monterey, California
 
 

Funding: JTO, ONR, NAVSEA

Twenty-eight years after the first operation of the short wavelength free electron laser (FEL) at Stanford University, there continue to be many important experiments, proposed experiments, and user facilities around the world. Properties of FELs in the infrared, visible, UV, and x-ray wavelength regimes are listed and discussed.

 
   
TUPP058 Calculations and Mitigation of THz Mirror Heating at the Jefferson Lab FEL
 
  • G.P. Williams, S.V. Benson, G.H. Biallas, D. Douglas, J.G. Gubeli, G. Neil, M.D. Shinn, S. Zhang
    Jefferson Lab, Newport News, Virginia
  • O.V. Chubar, P. D. Dumas
    SOLEIL, Gif-sur-Yvette
 
 

Funding: This work supported by the US Army Night Vision Lab, ONR, JTO, the Commonwealth of Virginia, the Air Force Research Laboratory, and DOE Contract DE-AC05-84ER40150. We thank Fred Dylla for his expert advice and encouragement.

Short bunches of electrons in the Jefferson Lab FEL emit multiparticle coherent edge radiation as they enter the dipole prior to the outcoupler mirror. This light is more collimated than synchrotron light and furthermore is modified by interference from the last chicane magnet after the high reflector. This light provides an additional heat load on the outcoupler in a wavelength range it was not designed to handle. We have performed calculations of this effect using a new extension of the Synchrotron Radiation Workshop code which, importantly, takes into account both acceleration and velocity (or Coulomb) terms of the emitted electric field. We have also measured THz properties of some of the mirrors. We show how the addition of a decompression chicane mitigates these problems.

 
   
TUPP059 Characterization and Performance of a High-Power Solid-State Laser for a High-Current Photocathode Injector 351
 
  • S. Zhang, D. Hardy, G. Neil, M.D. Shinn
    Jefferson Lab, Newport News, Virginia
 
 

Funding: This work supported by the Office of Naval Research, the Joint Technology Office, the Commonwealth of Virginia, the Air Force Research Laboratory, and by DOE Contract DE-AC05-84ER40150.

We report the characterization and performance of a diode-pumped, high-power, picosecond laser system designed for high-current photo-cathode accelerator injector at repetition rates of both 75MHz and 750MHz. Our characterization includes measurement of the system's amplitude stability, beam quality, pulsewidth, and phase noise for both frequencies.

 
   
TUPP060 Photoemission from Coated Surfaces: A Comparison of Theory to Experiment 355
 
  • K. Jensen
    NRL, Washington, DC
  • A. Balter
    ,
  • D.W. Feldman, N.A. Moody, P.G. O'Shea
    IREAP, College Park, Maryland
 
 

Funding: We gratefully acknowledge funding provided by the Joint Technology Office and the Office of Naval Research.

Photocathodes for FELs and accelerators will benefit from rugged and self-rejuvenating photocathodes with high QE at the longest possible wavelength. The needs of a high power FEL are not met at present by existing photocathode-drive laser combinations: requirements generally necessitate barrier-lowering coatings which are degraded by operation. We seek to develop a controlled porosity dispenser cathode, and shall report on our coordinated experimental and theoretical studies. Our models account for field, thermal, and surface effects of cesium monolayers on photoemission, and compare well with concurrent experiments examining the QE, patchiness, and evolution of the coatings. Field enhancement, thermal variation of specific heat and electron relaxation rates and their relation to high laser intensity and/or short pulse-to-pulse separation, variations in work function effects due to coating non-uniformity, and the dependence on the wavelength of the incident light are included. The status of methods by which the theory can be extended to semiconductor photocathodes and efforts to provide emission models to beam simulation codes is also treated.

 
   
TUPP061 FTIR Spectroscopy on Basic Materials in THz Region for Compact FEL-Based Imaging
 
  • H.J. Cha, Y.U. Jeong, B.C. Lee, S.-H. Park
    KAERI, Daejon
  • S.-H. Park
    Yonsei University, Seoul
 
 

Funding: This work was supported by Korea Research Foundation Grant (KRF-2004-042-C00053).

We are making experiments on THz(terahertz) imaging using a compact high power FEL (free-electron laser) which is operating as a users facility at KAERI. The wavelength range of output pulses is 100~1200 μm, which corresponds to 0.3~3 THz in the frequency region. We should select the optimum wavelength for the constituents of specimens to realize the imaging based on the THz FEL. A FTIR (Fourier-transform infrared) spectrometer was modified to measure the optical constants of the specimens in THz region. A polyester film of which thickness is 3.7 μm was used as a beam splitter of the spectrometer. In the case of normal incidence, the transmittance of the film was measured to be more than 90%, and the estimated loss by absorption was approximately 2% at the FEL frequency of 3 THz. Several tens of nanometer-thick-silver was coated on the polyester film to balance both transmission and reflection of THz waves in the beam splitter. We investigated FTIR spectroscopy on air, vapor and liquid water as test samples. As a preliminary step for the compact FEL-based biomedical imaging, FTIR spectroscopic experiments on the fundamental ingredients such as carbohydrates, fats, and proteins in THz region are also planned.

 
   
TUPP062 Investigation of X-Ray Harmonics in the Polarized Nonlinear Inverse Compton Scattering Experiment at UCLA 359
 
  • O. Williams, A. Doyuran, R.J. England, C. Joshi, J. Lim, J.B. Rosenzweig, S. Tochitsky, G. Travish
    UCLA, Los Angeles, California
 
 

An Inverse Compton Scattering (ICS) experiment investigating the polarized harmonic production in the nonlinear regime has begun which will utilize the existing terawatt CO2 laser system and 15 MeV photoinjector in the Neptune Laboratory at UCLA. A major motivation for a source of high brightness polarized x-rays is the production of polarized positrons for use in future linear collider experiments. Analytical calculations have been performed to predict the angular and frequency spectrums for various polarizations and different scattering angles. Currently, the experiment is running and we report the set-up and initial results. The advantages and limitations of using a high laser vector potential, ao, in an ICS-based polarized positron source are expected to be revealed with further measurement of the harmonic spectrum and angular characteristics.

 
   
TUPP063 Comparison of a ZGP:OPO with a Mark-III FEL as a Potential Replacement for Mid-Infrared Soft Tissue Ablation Applications
 
  • M.A. Mackanos, E.D. Jansen
    VUFEL, Nashville, Tennessee
  • A. Schwettman, D. Simanovski
    Stanford University, Stanford, Califormia
 
 

Funding: Medical Free Electron Laser Program of the Department of Defense under grant number F49620-01-1-0429

A Mark-III FEL, tuned to 6.45 μm has demonstrated minimal collateral damage and high ablation yield in soft tissue. Further clinical advances are limited due to the overhead associated with an FEL; alternative mid-IR sources are needed. The FEL parameters needed to carry out efficient ablation with minimal damage must be determined. Studies by this author have shown that the unique pulse structure of the FEL does not play a role in this process [1]. We focused on comparing the macropulse duration of the FEL with a ZGP-OPO. No difference in pulse structure between the two laser sources with respect to the ablation threshold of water and mouse dermis was seen. There is a difference between the sources with respect to the crater depths in gelatin and mouse dermis. At 6.1 μm, the OPO craters are 8 times the depth of the FEL ones. Brightfield imaging shows the classic ablation mechanism. The timescale of the crater formation, ejection, and collapse occurs on a faster scale for the OPO. Histology shows that the OPO provides for similar or less thermal damage than the FEL at all wavelengths tested. This research shows that a ZGP-OPO laser could be an alternative to the FEL for clinical applications.

[1] Mackanos, M.A., J.A. Kozub, and E.D. Jansen, The effect of free electron laser pulse structure on mid-infrard soft-tissue ablation: ablation metrics. Physics in Medicine and Biology, 2005. 50(8): p. 1871-1883.

 
   
TUPP065 Explosion of Small Xenon Clusters in a Shortwave Free-Electron Laser Pulse
 
  • M. Rusek, J. Krzywinski
    IP PAS, Warsaw
 
 

Explosion of small xenon clusters induced by short, intense short-wavelength pulses generated by a free-electron laser is studied theoretically using a Bloch-like hydrodynamic model. It is shown that energy is effectively absorbed by the plasma-like cloud of electrons bound to the cluster as a whole but released from individual atoms. During the Coulomb explosion of the cluster the energy acquired by the bound electrons moving freely inside the cluster is translated into kinetic energy of the outgoing ions. A lot of energy, however, is shown to stay in the excitations of individual outgoing ions. This is not measured in experiment where the absorbed energy is usually estimated based on the kinetic energy of the ions only.

 
   
TUPP066 Beyond the International Linear Collider: Driven by FEL with Energy Recovery at 5-10TeV
 
  • R. Hajima, T. Tajima
    JAEA/FEL, Ibaraki-ken
 
 

The international linear collider (ILC) at the extreme high energy frontier provides the best hope for the scientist to probe the finenst structure of matter and its origin and perhaps even the origin of the Universe. The technology that employs is based on superconducting RF technology. This technology may usher in a new era for the development of superconducting accelerator technology. On the other hand, the gradient that is allowed in such an accelerator is limited. If one wishes something beyond this after one learns the physics at such high energies(~0.5TeV) and utilizing such technology, one may need a new way to employ the supeconducting technology in providing high gradient compact accelerators. Inspired by a former work of 5-TeV colliders based on solid-state tera-watt lasers [1], we explore 5-10 TeV linear colliders driven by free-electron lasers equipped with energy-recovery system. A preliminary design study suggests that a 5-10 TeV collider with the luminosity of 10(34) can be realized by multi-stage laser acceleration.

[1] M. Xie et al., AIP Conference Proceedings 398, 233 (1997).

 
   
TUPP067 Quantum Theory of High-Gain Free-Electron Lasers 363
 
  • R. Bonifacio
    INFN-Milano, Milano
  • N. Piovella
    Universita' degli Studi di Milano, MILANO
 
 

We formulate a quantum linear theory of the N-particle free-electron laser Hamiltonian model, quantizing both the radiation field and the electron motion, in the steady state regime. Quantum effects such as frequency shift, line narrowing, quantum limitation for bunching and energy spread and minimum uncertainty states are described. Using a second quantization formalism we demonstrate quantum entanglement between the recoiling electrons and the radiation field.

 
   
TUPP068 Analytical Solution for FEL nd CARL Nonlinear Regime 367
 
  • R. Bonifacio
    INFN-Milano, Milano
 
 

We derive a simple analytical solution for the non linear regime in the quasi steady state situation of the high gain Free Electron Laser (FEL) and Collective Atomic Recoil Lasing (CARL) model which up to now have been described only numerically. We show that the system can be described by an exact reduced Hamiltonian which does not contain the field explicitly. We give simple analytical expressions for the field amplitude, frequency shift, bunching factor, particle average momentum and momentum spread, as well as the period of oscillations around the quasi steady state solution, in very good agreement with the numerical values.