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Page count: 15

A near back-scattering imaging diagnostic system is being implemented on the first quad of beams on the National Ignition Facility. This diagnostic images diffusing scatter plates, placed around the final focus lenses on the NIF target chamber, to quantitatively measure the fraction of light back-scattered outside of the incident cone of the focusing optics. The imaging system consists of a wide-angle lens coupled to a gated CCD camera, providing 3mm resolution over a 2m field of view. To account for changes of the system throughput due to exposure to target debris the system will be routinely calibrated in situ at 532nm and 355nm using a dedicated pulsed laser source. The diagnostic will be described and recent results will be presented. Work performed under the auspices of the U.S. Department of Energy by UC/Lawrence Livermore National Laboratory under Contract No. W-7405-ENG-48.