Coherence properties of a quasi-Gaussian submilliradiant divergence soft-x-ray laser pumped by capillary discharges

Abstract

The coherence properties of a $46.9\text{\ensuremath{-}}\mathrm{nm}$ soft-x-ray laser beam produced in a capillary discharge plasma have been investigated. The beam is produced in a regime that is free from the effect of refraction defocusing, with a divergence of only $0.5--0.6\phantom{\rule{0.3em}{0ex}}\mathrm{mrad}$. The discharge plasma is produced in capillary channels with length of $45\phantom{\rule{0.3em}{0ex}}\mathrm{cm}$, where the Fresnel number of the gain medium is of the order of unity. The full laser energy is about $300\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{J}$. The spatial coherence of the laser has been experimentally investigated using a Young's double-slit interferometer and analyzed assuming a Gaussian Schell-model source and the generalized Van Cittert--Zernike theorem. We demonstrate the achievement of almost full spatial coherence and a near-Gaussian intensity distribution.