SPATIAL COHERENCE OF PREPULSE-INDUCED NEON-LIKE X-RAY LASERS

We report a series of Young's double-slit experiments to measure the t ransverse spatial coherence of prepulse-induced low-Z neonlike x-ray l asers for two prepulse levels. The experiments were performed using th e Asterix IV iodine laser with a prepulse 5 ns before the main pulse. The main pulse energy was 400 J, with a pulse duration of 450 ps. Two slit separations of 80 and 110 mu m were used to measure coherence in the vertical direction. We also present data for the horizontal transv erse coherence, obtained with only a single-slit separation of 110 mu m. The equivalent incoherent source sizes of the x-ray lasers along th e vertical direction, as derived by the Van Cittert-Zernike theorem, w ere found to be 100-120 mu m for the 1.5% prepulse, and 110-170 mu m f or the 15% prepulse level, respectively. Compared to the near-field pa tterns, the equivalent source sizes obtained with the lower prepulse l evel (1.5%) are found to be significantly smaller, indicative of an en hancement of the spatial coherence by the gain medium. The observation of a higher degree of coherence for the 1.5% prepulse is corroborated by simulations using a two-dimensional hydrocode and a ray-tracing po stprocessor.