Spatial coherence of x-ray laser emission from neonlike germanium after prepulse

The time-integrated spatial coherence of neonlike germanium x-ray laser radiation has been studied with a new dispersing coherence diagnostic. Angle-dependent spatial coherence data are recorded by sampling the diverging beam at each lasing wavelength in several directions simultaneously. Measurements of the spatial coherence, and hence effective source sizes, relevant to the output beams from double-slab targets for the J = 2-1 spectral lines at wavelengths 28.6, 23.6, and 23.2 nm and for the J = 0-1 line at 19.6 nm show differences, which indicate different conditions in the plasma volume amplifying these emissions. Targets are pumped by subnanosecond pulse drivers, with and without a prepulse, but 19.6 nm emission is detected only in the prepulsed case. The differences are discussed in terms of the time evolution of the spectral lines. (C) 1997 Optical Society of America.