JASRI/SPring-8, Hyogo-ken
JAEA/Kansai, Kyoto
SOLEIL, Gif-sur-Yvette
RIKEN/SPring-8, Hyogo
The University of Tokyo, Tokyo
Keio University, Kanagawa-ken
RIKEN, Saitama
NTT Corp., Kanagawa-ken
KEK, Tsukuba
A seeded FEL is the most promised way to generate fully coherent radiation in a short-wavelength region. After the improvement of the laser and HHG system at the SCSS test accelerator, we have succeeded the amplification of the seed, for the first time, in the plateau region. The wavelength of the seed is 61.5 nm, which is the 13th harmonic of a Ti:Sa laser, and clear intensity increase and spectral narrowing by the FEL was observed. Although there still remains room for optimization of the transverse matching and synchronization of the seed, this result leads to realization of a fully coherent light source to users in VUV and soft x-ray regions.
SOLEIL, Gif-sur-Yvette
PhLAM/CERCLA, Villeneuve d'Ascq Cedex
Nagoya University, Nagoya
UVSOR, Okazaki
JASRI/SPring-8, Hyogo-ken
In FEL oscillator, a desynchronisation between the electron-bunch passage frequency and the repetition rate of the laser can lead to instability, characterised by erratic longitudinal shape of the emitted light pulses. We show that this instability can be controlled using a simple feedback system which consist in re-injecting in the cavity a part of the emitted light. Analytical, numerical and experimental studies on the UVSOR-II storage ring have been performed, and show that the energy needed to achieved the control can be extremely weak, in practical higher than the noise level[1]. We also show that another important parameter is the phase of the re-injected signal with respect to the light in the cavity. Depending of the value of this phase, we can observe a shift of the emitted light wavelength, which can go with a modulation of the laser pulse envelop. Both of this two phenomenas are quantitatively analysed.
[1] C. Evain, C. Szwaj, S. Bielawski, M. Hosaka, A. Mochihashi, M. Katoh, and M.-E. Couprie, Phys. Rev. Lett. {10}2, 134501 (2009)
SOLEIL, Gif-sur-Yvette
PhLAM/CERCLA, Villeneuve d'Ascq Cedex
LAL, Orsay
University of Erlangen-Nuremberg, Erlangen-Nuremberg
We investigate a dynamical behaviors occurring in single-pass free electron lasers (FELs), depending on the electron beam, undulator and seed laser parameters. We put in evidence a complex spatiotemporal deformation of the amplified pulse, leading ultimately to a pulse splitting effect with two sub-pulses. This phenomenon has been first observed in PERSEO simulations in the case of ARC-EN-CIEL project studies, and then been analyzed more in details with the Colson-Bonifacio FEL equations. This studies reveal that slippage length as well as the seed laser pulse wings are the main ingredients of this dynamics [1]. We show that the splitting results from the nonhomogeneous saturation of the gain by the optical field copropagating with the electron beam.
M.Labat et al. “Pulse-splitting in short wavelength seeded free electron laser,” Phys. Rev. Lett. {10}3, 264801 (2009)
ENEA C.R. Frascati, Frascati (Roma)
INFN/LNF, Frascati (Roma)
Istituto Nazionale di Fisica Nucleare, Milano
CEA, Gif-sur-Yvette
SOLEIL, Gif-sur-Yvette
Università di Roma II Tor Vergata, Roma
LUXOR, Padova
LOA, Palaiseau
UCLA, Los Angeles, California
INFN-Roma, Roma
Rome University La Sapienza, Roma
ISM-CNR, Rome
SPARC is a single pass free electron laser test facility realized in collaboration between the main Italian research institutions and devoted to experiments of light amplification in different beam conditions. While the laser was commissioned in self amplified spontaneous emission (SASE) mode during the last year, the operation in seeded mode has been recently demonstrated. The amplifier has been seeded with the second harmonic of the Ti:Sa driver laser generated in a crystal and with higher order VUV harmonics generated in a gas cell. The comparison between seeded and unseeded FEL emission will be discussed. The laser has been also operated in a new SASE configuration with a strongly chirped longitudinal e-beam phase space resulting from the RF compression. The chirp has been compensated by accordingly tapering the undulator gaps. Spectra with and without taper have been collected. An increase of about a factor 5 of the pulse energy in combination with spectra with a single longitudinal coherence region have been detected in presence of the taper. The combination of the chirp with the input seed is under study.