Demonstration of a soft-x-ray laser at 13.9 nm with full spatial coherence

We have demonstrated the generation of a highly coherent x-ray laser at 13.9 nm by an oscillator-amplifier configuration with two targets. In the oscillator-amplifier configuration, a seed x-ray laser beam from one target is injected into a plasma amplifier at another target. When the propagation of the x-ray laser beam is not affected by refraction in the amplifier, a highly coherent x-ray laser beam with small divergence of 0.2 mrad is generated. The observed divergence is close to the diffraction limited value, and this beam has full spatial coherence.