Session: TUCxS - 31 Aug 2004
FEL Oscillators

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.