Development of a full spatial coherent X-ray laser at 13.9 nm

We have succeeded in developing a laser-pumped X-ray laser with full spatial coherence at 13.9 nm. The X-ray laser beam with a very small divergence of 0.2 mrad was generated from double target experiments, where a seeding light from the first laser medium was amplified in the second laser medium. The observed divergence was close to the diffraction limit value within a factor of two. The seeding light was amplified in the second medium without refraction influence and the gain coefficient was 7.9 cm^-1. From the measurement of visibility, it was found that the spatial coherent length was longer than the beam diameter. PACS 41.50+h; 42.55.Vc