Characterization of Isolated Defects for NIF Targets Using PSDI with an Analysis of Shell Flipping Capability

Capsules for the National Ignition Facility require measurement of isolated defects on the capsule surface. A phase-shifting diffraction interferometer (PSDI) is used to identify, locate, and measure defects by capturing 71 overlapping ~500-m-diam charge coupled device height maps for software analysis. Using capsules with drilled holes for the purpose of alignment, PSDI data were confirmed with atomic force microscopy by comparing defect data from corresponding equatorial bands. We explored the limitations of the PSDI resulting from unwrapping errors caused by defect slopes greater than the Nyquist sampling theorem. White light interferometry proved to be a useful complementary tool to measure defects that could not be unwrapped by the analysis software. Implementing the PSDI in conjunction with the shell flipper, both developed at Lawrence Livermore National Laboratory, allowed for full mapping of shell surfaces by mounting corresponding hemispheres onto the PSDI within a 2-deg accuracy.