Collaborations : M.-E. Couprie et al., SOLEIL Synchrotron (St-Aubin, France)
T. Hara et al., SPring8 Compact SASE Source (SCSS), XFEL Project/RIKEN (Hyogo, Japan)
L. Giannessi et al., ENEA & INFN/LNF (Frascati, Italy)
For producing intense ultra-short pulses in the XUV, the combination of laser- and accelerator-based sources will obviously play a major role in the design of the fourth-generation FEL. In the collaboration with Soleil-Synchrotron and SPring-8 Compact SASE Source (SCSS, SPring-8, Japan, SASE is for Self-Amplified Spontaneous Emission), we have recently coupled a seed harmonic source at 160 nm (5th harmonic of IR laser) to the LINAC FEL amplifier [G. Lambert, T. Hara et al., Nature Physics 4, 296 (2008)].
Amplification has been demonstrated at low seed level (few nJ per pulse) with large amplification factors (~500 for the seed and ~2500 for the SASE-FEL). The saturation of the FEL emission is reached faster than in the SASE mode. Moreover, the spectral properties of the seeded FEL are improved. We are now working on the extrapolation to shorter seed wavelength. A parallel collaborative program has been developed at SPARC LINAC FEL (ENEA & INFN/LNF, on support of EUROFEL design studies); its objective is to demonstrate the High Gain Harmonic Generation (HGHG: the FEL cavity is tuned on the seed harmonic).