Broadband Smoothing of Laser Pulses for Imprint Reduction in Direct-Drive Inertial Confinement Fusion*

In direct-drive inertial confinement fusion, an ensemble of laser beams irradiates a spherical capsule of deuterium--tritium fuel encased in a thin outer ablator. Early in the drive, intense speckles within the beams locally heat the ablation surface imprinting small{\-}scale density nonuniformities. Ultimately, this imprint can severely limit the fusion yield by seeding hydrodynamic instabilities that cause the capsule to break up during compression. Broad{\-}bandwidth lasers can mitigate imprint with rapidly moving speckle patterns that smooth the intensity profile faster than the ablation surface can hydrodynamically evolve. Here we explore the efficacy of imprint{\-}mitigation techniques enabled by broad{\-}bandwidth lasers.