DEPENDENCE OF SPATIAL COHERENCE OF 23.2-23.6-NM RADIATION ON THE GEOMETRY OF A MULTIELEMENT GERMANIUM X-RAY LASER TARGET

The spatial coherence of a nanosecond pulsed germanium collisionally e xcited x-ray laser is measured experimentally for three target configu rations. The diagnostic is based on Young's slit interference fringes with a dispersing element to resolve the 23.2- and 23.6-nm spectral li nes. Target configurations include a double-slab target, known as the injector, and geometries in which the injector image is image relayed to seed either an additional single-slab target or a second double-sla b target. A special feature of this study is the observation of the ch ange in the apparent source size with angle of refraction across the d iverging laser beam. Source sizes derived with a Gaussian source model decrease from 44 mu m for the injector target by a variable factor of as much as 2, according to target configuration, for beams leaving th e additional amplifiers after strong refraction in the plasma. (C) 199 8 Optical Society of America [S0740-3224(98)00810-8].