Dark-field study of rear-side density structure in laser-accelerated foils

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Abstract
A dark-field, laser-probing diagnostic has produced the first high-resolution photographs of density structure on the rear side of laser-accelerated foils. This diagnostic allows the preferential sampling of the steep-gradient region of an expanding plasma and permits two-dimensional, multiple-time recordings on a single photograph. The studies are aimed at understanding the early-time physics of target implosions for inertial confinement fusion. Both long (500-ps) and short (150-ps) probe pulses were used to study the rear-side plasmas of thin foils accelerated by the rocketlike reaction to a hot plasma ablated from the front side by the laser radiation. The longer pulse results, both for angular scatter and the lifetime of small, transverse structure, imply a relatively cold (∼1 eV) rear-side plasma. The short pulses provide high-resolution photographs of the complete structure. These observations are relevant to two of the basic requirements of inertial confinement fusion: cold fuel isentrope and implosion symmetry.