FEL emissions at 160 NM in seeded configuration on the SCSS test accelerator

Today, single-pass Free-Electron Lasers (FEL) produced a highly bright radiation, the Self Amplified Spontaneous Emission (SASE), which spectral and temporal profiles are composed of a series of spikes. We have demonstrated the strong and coherent amplification of the 5^th harmonic of a Ti: Sa laser (800 nm, 10 Hz, 100 fs) generated in a gas cell, i.e. 160 nm, by the SCSS (SPring-8 Compact SASE Source, Japan) Test Accelerator FEL. This is obtained by overlapping transversally, spectrally and temporally the external harmonic source in the in-vacuum undulator with the electron beam (150 MeV, 10 Hz, 1 ps). With only one undulator section, the 160 nm seeded emission achieves three orders of magnitude higher intensity than the unseeded one, and presents a quasi perfect Gaussian shape in the spectral distribution. With two undulator sections, the seeded FEL spectrum reveals first effects of saturation.