Complementary Optical and Radiographic Measurement of Laser Imprint Mitigation on Nike

Laser imprint mitigation using hybrid (indirect-direct) drive with a high-Z coating has been shown to have an order-of-magnitude reduction in the laser non-uniformity seeding of hydrodynamic instabilities on the Nike KrF laser [Obenschain. PoP 9, 9, 2234 (2002); Karasik, PRL 114, 085001 (2015), https://doi.org/10.1063/1.1464541, https://doi.org/10.1103/PhysRevLett.114.085001] and on Omega EP 3ω Nd:glass laser [Karasik, PoP 28, 032710 (2021), https://doi.org/10.1063/5.0042454]. Raleigh-Taylor amplification of laser imprint has been required to diagnose this using radiography. Recent installation of high resolution 2D VISAR on Nike allowed sensitive measurement of the imprint reduction due to the high-Z coating independent of RT amplification [J. Oh, PoP 28, 032704 (2021), https://doi.org/10.1063/5.0039395].  Reduction in imprint seeding is also expected with increased laser bandwidth (shorter coherence time).  Measurements of imprint for ISI smoothing with bandwidths in the range 0.3 – 3 THz on Nike will be presented and compared with high resolution FASTrad3D simulations. Work is supported by the US DOE/NNSA.