FEL Oscillators

FRBIS02 Overview of Terahertz Radiation Sources
Gian Piero Gallerano (ENEA C.R. Frascati, Frascati - Roma), Sandra G. Biedron (ANL, Argonne, Illinois)

Although Terahertz (THz) radiation was first observed about hundred years ago, the corresponding portion of the electromagnetic spectrum has been for long time considered a rather poorly explored region at the boundary between the microwaves and the infrared. This situation has changed during the past ten years with the rapid development of coherent THz sources, such as quantum cascade laser, diodes, optically pumped solid state devices and novel free electron devices, which have in turn stimulated a wide variety of applications from material science to telecommunications, from biology to biomedicine. In this paper we review the development and perspectives of THz radiation sources and their applications with particular emphasis on the research effort carried out and planned in the frame of various European programs.

TUBOS03 High Average Power Operation of a Scraper-Outcoupled Free-Electron Laser
Michelle D. Shinn, Chris Behre, Stephen Vincent Benson, Michael Bevins, Don Bullard, James Coleman, L. Dillon-Townes, Tom Elliott, Joe Gubeli, David Hardy, Kevin Jordan, Ronald Lassiter, George Neil, Shukui Zhang (Jefferson Lab, Newport News, Virginia)

We describe the design, construction, and operation of a high average power free electron laser using scraper outcoupling. Using the FEL in this all-reflective configuration, we achieved approximately 2 kW of stable output at 10 um. Measurements of gain, loss, and output mode will be compared with our models.

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.

TUCOS02 High Power Lasing in the IR Upgrade FEL at Jefferson Lab
Stephen Vincent Benson, Kevin Beard, Chris Behre, George Herman Biallas, James Boyce, David Douglas, Fred Dylla, Richard Evans, Al Grippo, Joe Gubeli, David Hardy, Carlos Hernandez-Garcia, Kevin Jordan, Lia Merminga, George Neil, Joe Preble, Michelle D. Shinn, Tim Siggins, Richard Walker, Gwyn Williams, Byung Yunn, Shukui Zhang (Jefferson Lab, Newport News, Virginia), Hiroyuki Toyokawa (KEK, Ibaraki)

We report on progress in commissioning the IR Upgrade facility at Jefferson Lab. Operation at high power has been demonstrated at 5.7 microns with over 4 kW of continuous power output and a recirculated electron beam power of up to 800 kW. We report on the features and limitations of the present design and on efforts to increase the power to over 10 kW.

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.

THPOS09 Electron-Beam Stabilization for the European Storage-Ring Free-Electron Laser at Elettra
Mauro Trovò, Daniele Bulfone, Miltcho B. Danailov, Giovanni De Ninno, Bruno Diviacco, Vincenzo Forchi`, Marco Lonza (Elettra, Basovizza, Trieste), Luca Giannessi (ENEA C.R. Frascati, Frascati - Roma)

The temporal structure of the storage-ring free-electron laser at Elettra shows high sensitivity to electron-beam instabilities. In fact, even small beam orbit oscillations (of the order of few microns) may perturb the FEL dynamics and periodically switch off the laser. In order to improve the FEL operation and performance, a longitudinal multi-bunch feedback and a local orbit feedback have been activated. This paper reports on the beneficial effect of these feedback systems. Plans for a future "slow" longitudinal feedback are also briefly described.

THPOS15 Tunability and Power Characteristics of the LEBRA Infrared FEL
Toshinari Tanaka, Ken Hayakawa, Yasushi Hayakawa, Akira Mori, Kyoko Nogami, Isamu Sato, Kazue Yokoyama (LEBRA, Funabashi), Ken-ichiro Ishiwata, Koichi Kanno, Keisuke Nakao, Takeshi Sakai (Graduate School of Science and Technology, Funabashi)

Application of the infrared (IR) Free-Electron Laser (FEL) was started in October 2003 at the Laboratory for Electron Beam Research and Application (LEBRA) of Nihon University. The FEL system consisted of silver-coated copper mirrors has demonstrated wavelength tunability ranged from 940 to 6100 nm as a function of the electron energy and the undulator K-value. Wavelength dependence of the FEL output power has been measured in term of different electron beam currents, electron energies and the undulator K-values. Approximate 25 mJ/macropulse has been obtained in the range 2 to 3 microns, which corresponds to peak power of 2 MW, provided that the FEL pulse length is 0.4 ps as resulted from the measurement by an interferometric method. The power decrease observed in the longer wavelength range is due to a large diffraction loss in the FEL guiding optics and the vacuum ducts.

THPOS17 Status of Institute of Free Electron Laser, Osaka university
Hiroshi Horiike, Makoto R. Asakawa, Kunio Awazu, Manabu Heya, H. Kondo, Y. Naito, Sachiko Suzuki, N. Tsubouchi (OU-iFEL, Hirakata, Osaka)

Research activities at iFEL Osaka, including development of FEL systems and application programs, will be reviewed.

THPOS22 Misalingment Tolerance of a Hole-Coupling Optical Resonator for JAERI ERL-FEL
Ryoji Nagai, Ryoichi Hajima, Nobuhiro Kikuzawa, Eisuke John Minehara, Nobuyuki Nishimori, Masaru Sawamura (JAERI/FEL, Ibaraki-ken)

The misalignment tolerance of a hole-coupling optical resonator for the JAERI ERL-FEL is estimated with a wavelength of 22 μm by a Fox-Li procedure simulation code. The output power stability depends on the misalignment tolerance. It is found that the misalignment tolerance of the hole-coupling mirror is less than the non-coupling mirror and the offset of the non-coupling mirror is compensable tilting the mirror.

THPOS27 Optimization of the NIJI-IV FEL System for the Coherent Harmonic Generation in a Q-switched Regime
Hiroshi Ogawa, Norihiro Sei, Kawakatsu Yamada, Masato Yasumoto (AIST-PRI, Tsukuba, Ibaraki)

The Coherent Harmonic Generation (CHG) in the VUV region at the storage ring NIJI-IV has been numerically investigated. The harmonic radiation is produced in an FEL oscillator with a hole-coupled resonator including a 6.3-m optical klystron ETLOK-II. The evolution of light pulses through Q-switched FEL process is simulated using the code GENESIS1.3 and its extended code. The parameters of the NIJI-IV FEL system will be optimized for different electron-beam energy of 310-450MeV and optical cavity configurations.

THPOS36 Preliminary Design of a Synchronized Narrow Bandwidth FEL for Taiwan Light Source
Wai Keung Lau, June Rong Chen, Tai Ching Fan, Feng Zone Hsiao, Kuo Tung Hsu, Ching-Shiang Hwang, Chin Cheng Kuo, Guo Huei Luo, Duan Jen Wang, Jau Ping Wang, Min Huey Wang (NSRRC, Hsinchu), Cheng Wei Chen, Huan Yang Chen (NTHU, Hsinchu)

Design study of a narrow line-width, high power IR-FEL facility has been carried out at NSRRC. This machine is designed to synchronize with the U9 undulator radiation of Taiwan Light Source and therefore provide new opportunity for chemical dynamics and condensed matter research. It has been proposed to use a super-conducting linac to provide a 60 MeV high quality electron beam to drive a 2.5-10 microns FEL oscillator with U5 undulator. Operating this linac in energy recovery mode will also be considered as an option to improve overall system effeciency and reduce heat loss and radiation dosage at the beam dump. Performance requirements and outcomes from this preliminary design study will be reported.

THPOS46 Numerical Modeling of the Novosibirsk Terahertz FEL and Comparison with Experimental Results
Oleg Alexandrovich Shevchenko, Alexander Viktorovich Kuzmin, Nikolai Aleksandrovich Vinokurov (BINP, Novosibirsk)

Recently a new high-power terahertz FEL has been put in operation at the Siberian Center for Photochemical Research in Novosibirsk. The first lasing at the wavelength near 140 micrometer was achieved in April 2003. Since then some experimental data were obtained which required theoretical explanation. In this paper we use a simple 1-D model for numerical simulations of the FEL operation. The model is based on excitation of multiple longitudinal radiation modes by charged discs. We restrict our consideration to only the fundamental transverse mode. This approximation is valid in the case of long-wave FELs. We compare the results of numeric simulations with some analytical estimates and experimental data.

THPOS47 Start-To-End Simulations of the Energy Recovery Linac Prototype FEL
Christopher Gerth, Marion Bowler, Bruno Muratori, Hywel Owen, Neil R. Thompson (CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire), Bart Faatz (DESY, Hamburg), Brian W.J. McNeil (Strathclyde University, Glasgow)

Daresbury Laboratory is currently building an Energy Recovery Linac Prototype (ERLP) that serves as a testbed for the study of beam dynamics and accelerator technology important for the design and construction of the proposed 4th Generation Light Source (4GLS) project. Two major objectives for the ERLP are the operation of an oscillator infra-red FEL and demonstration of energy recovery from an electron bunch with an energy spread induced by the FEL. In this paper we present start-to-end simulations including the FEL of the ERLP. The beam dynamics in the high-brightness injector, which consists of a DC photocathode gun and a super-conducting booster, have been modelled using the particle tracking code ASTRA. After the main linac, in which the particles are accelerated to 35 MeV, particles have been tracked with the code ELEGANT. The 3D code GENESIS was used to model the FEL interaction with the electron beam. Different modes of operation and their impact on the design of the ERLP are discussed.

THPOS59 Stability of a Short Rayleigh Range Laser Resonator with Misaligned or Distorted Mirrors
Peter P. Crooker, Joseph Blau, William B. Colson (NPS, Monterey, CA)

Motivated by the prospect of constructing an FEL with short Rayleigh length in a high-vibration shipboard environment, we have studied the effect of mirror vibration and distortion on the behavior of the fundamental optical mode of a cold-cavity resonator. A tilt or transverse shift of a mirror causes the optical mode to rock sinusoidally about the original resonator axis. A longitudinal mirror shift or a change in the mirror’s radius of curvature causes the beam diameter at a mirror to dilate and contract with successive impacts. Results from both ray-tracing techniques and wavefront propagation simulations are in excellent agreement.

THPOS60 Gain and Coherent Radiation from a Smith-Purcell Free-Electron Laser
Charles A. Brau, Heather L. Andrews, Charles H. Boulware, Jonathan D. Jarvis (Vanderbilt/DPA, Nashville - Tennessee)

We have developed a new theory to describe the gain of a Smith-Purcell FEL. The theory shows that the electrons interact with an evanescent mode whose frequency lies slightly below the frequency range of Smith-Purcell radiation, and whose group velocity is negative. Computations indicate that very high gain should be observed even at very low current with suitable bright electron beams. An experiment is under construction to test these predictions.