Characterization of an OFI seeded soft x-ray laser

Since the first seeding of an OFI soft x-ray laser in 2004, we progressed towards the full characterization of the output beam. The final is to be able to deliver to users well-known beam. Temporal as well as spatial parameters have been measured for different conditions of amplification. We observed a strong enhancement of the spatial coherence due to the amplification process with a far-field pattern exhibiting an airy-like shape. The gain zone having strong discontinuity behaves like a hard pinhole. Spatial filtering has been also observed on the wave front (δ/5 root-mean-square, rms, before seeding and δ/20 rms after amplification). Temporal coherence has been studied thanks to the use of a Fourier- Transform spectrometer. Spectral widths, δδ/δ, around 10 -5 have been measured for different plasma lengths or gas pressures. Departure from Gaussian shape has been clearly observed on the spectral line for some cases.