Spatial coherence measurements of a 13.2 nm transient nickel-like cadmium soft x-ray laser pumped at grazing incidence.

The spatial coherence of a 13.2 nm transient collisional Ni-like Cd soft X-ray laser pumped at 23 degrees grazing incidence was measured in a series of Young's double-slit experiments. We observed pronounced fringe visibility variations associated with microstructures in the beam's intensity profile. The transverse coherence length was measured to be about 1/20 of the beam diameter and did not significantly improve with longer plasma columns. The equivalent incoherent source size is determined to be 10 mum and the laser's peak spectral brightness ~ 3 x 10(23) photons/sec/mm(2)/mrad(2) within less than 0.01% spectral bandwidth.