Spatially resolved B-integral measurements on the NIF laser

The National Ignition Facility (NIF), located at Lawrence Livermore National Laboratory, is the world’s largest and highest-energy laser system. NIF’s 192 intense laser beams can deliver more energy than any previous laser system with a design point of 1.8 MJ of UV and 500 TW peak power. Efforts are currently underway to better understand the NIF performance and its limitations. One goal of recent and future campaigns is to better understand the accumulation of Bintegral within the NIF laser using existing diagnostics, as well as the Precision Diagnostic System (PDS). Among these diagnostics, the Shack-Hartmann (SH) sensor in the Output Sensor Package (OSP), a standard NIF diagnostic, and the dedicated PDS Radial Shearing Interferometer (RSI) both measure the wavefront of the beam. Using these diagnostics in concert with the NIF Programmable Spatial Shaper (PSS), which is used to tailor arbitrary spatial beam profiles, we have performed integrated experiments to study the B-Integral induced wavefront through the entire NIF main laser. We propagated a probe beam with a slowly varying spatial intensity profile through the NIF laser to produce a spatially varying B-Integral induced wavefront at the laser output, from which we obtained the magnitude of the B-Integral of the system. We present these direct measurements of the spatially resolved B-Integral induced wavefront scaled for the first time from a table-top experiment to a fusion-class laser chain. These measurements are compared to results of current simulations using Virtual Beamline (VBL) software.