Measurements of Laser Imprint with High-Z Coated targets on Omega EP

Previous experiments on Nike KrF laser $(\lambda=248~nm)$ at NRL found that a thin (400--800$\AA$) high-Z (Au or Pd) overcoat on the laser side of the target is effective in suppressing broadband imprint[Obenschain et al., PoP 9, 2234 (2002); Karasik et al.,PRL 114, 085001 (2015)] and reducing ablative Richtmyer-Meshkov growth [ http://meetings.aps.org/link/BAPS.2008.DPP.CO5.9 ]. The overcoat initially absorbs the laser and emits soft x-rays that ablate the target, forming a large stand-off distance between laser absorption and ablation and driving the target at higher mass ablation rate. Implementation of this technique on the frequency-tripled Nd:glass (351~nm) NIF would enable a wider range direct drive experiments there. To this end, we are carrying out experiments using the NIF-like beams of Omega EP. Analogous to experiments on Nike, areal mass perturbations due to RT-amplified laser imprint are measured using curved crystal imaging coupled to a streak camera. High-Z coating dynamics and target trajectory are imaged side-on. First results indicate that imprint suppression is observed, albeit with thicker coatings. Work supported by the Department of Energy/NNSA.