Spatial coherence of prepulse-induced neonlike x-ray lasers

摘要

We report a series of Young's double-slit experiments to measure the transverse spatial coherence of prepulse-induced low-Z neonlike x-ray lasers for two prepulse levels. The experiments were performed using the 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 transverse coherence, obtained with only a single-slit separation of 110 mu m. The equivalent incoherent source sizes of the x-ray lasers along the vertical direction, as derived by the Van Cittert-Zernike theorem, were found to be 100-120 mu m for the 1.5% prepulse, and 110-170 mu m for the 15% prepulse level, respectively. Compared to the near-field patterns, the equivalent source sizes obtained with the lower prepulse level (1.5%) are found to be significantly smaller, indicative of an enhancement 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 postprocessor. [References: 40]