Katoh, M.

Paper	Title	Page
MOPPH001	Coherent Harmonic Generation on UVSOR-II Storage Ring	37
	M. Labat, G. Lambert CEA, Gif-sur-Yvette M.-E. Couprie SOLEIL, Gif-sur-Yvette T. Hara RIKEN Spring-8 Harima, Hyogo M. Hosaka, M. Katoh, A. Mochihashi, M. Shimada, J. Yamazaki UVSOR, Okazaki D. Nutarelli LAC, Orsay Y. Takashima Nagoya University, Nagoya
	In the Coherent Harmonic Generation Free Electron Laser configuration, an external seed signal, a commercial laser source, is focused inside the first undulator. The interaction between the electron beam and this seed leads to a more coherent light emission. Such devices are very promising for short wavelength operation with a rather compact facility. Experiments have been performed on the UVSOR-II Storage Ring (Okazaki, Japan) with electrons stored at 600 MeV, and using a 2.5 mJ Ti:Sa laser at 800 nm wavelength, 1 kHz repetition rate, and 100 fs up to 2 ps pulse duration, allowing emission at 266 nm. This third harmonic has been characterised versus various parameters. Optimizations have been realized on the electron beam and laser synchronisation, seed characteristics (focussing point, energy, and pulse duration). The dependency of the harmonic signal on the gain (undulator gap, magnetic functions) has also been studied. Theory is compared to experiment using both analytical models and simulation. These encouraging results make UVSOR-II storage ring an active test facility for Coherent Harmonic Generation scheme, as well as a potential VUV source for users experiments.
TUPPH023	High Power Deep UV Lasing on the UVSOR-II Storage Ring FEL	368
	M. Hosaka, M. Katoh, A. Mochihashi, M. Shimada UVSOR, Okazaki T. Hara RIKEN Spring-8 Harima, Hyogo Y. Takashima Nagoya University, Nagoya
	Thanks to an improved quality of the electron beam at the UVSOR-II storage ring, we have obtained a high power FEL lasing of 0.25 W in the deep UV region around 215 nm. The beam emittance of the UVSOR-II storage ring are improved by factor 6 in 2002. Recently we have renewed an rf accelerating cavity, which can be operated in about 3 time higher cavity voltage ( 150 kV) than the previous cavity voltage. All these improvement increased the FEL gain and we have obtained FEL lasing around 215 nm using Al2O3/SiO2 multilayer mirrors. In the primarily lasing experiment, the storage ring was operated at an electron energy of 600 MeV, which is ordinary energy for FEL experiments. Then we increased the energy to 750 MeV and obtained an extracted power of 0.25 W. The deep UV FEL has been already applied to an users irradiation experiment. Two other application experiments are planned now. In the presentation, the latest status of UVSOR-II FEL will be reported.
THAAU04	Influence of Optical Feedback on the Coherence Properties of FEL Oscillators	512
	S. Bielawski, C. Szwaj PhLAM/CERCLA, Villeneuve d'Ascq Cedex M.-E. Couprie CEA, Gif-sur-Yvette M. Hosaka, M. Katoh, A. Mochihashi UVSOR, Okazaki
	When detuned, the output of a FEL oscillator is dominated by a transient amplification of the spontaneous emission noise (SE). Here, we show that FEL oscillators in this situation appear to display a strong sensitivity to optical feedback. From a Dattoli-Elleaume type modeling, we show that a very small amount of reinjected power (typically <<1·10-8 in the case of the UVSOR SR-FEL) modifies dramatically the FEL operation. In particular, we demonstrate experimentally and numerically a strong spectral narrowing, correlated with a disappearance of the laser pulse microstructures. This is also accompanied by a suppression of SR-FEL instabilities for a wide range of parameters (half of the detuning curve). These topics (strong amplification of SE noise, and control using tiny reinjection), are of course more general. We propose a theoretical approach of these questions, using in particular the concept of convective instabilities.
	Slides
	Talk