Overview of the line-imaging VISAR diagnostic at the National Ignition Facility (NIF)

Optical diagnostics are currently being designed to analyze high-energy density physics experiments at the National Ignition Facility (NIF). Two line-imaging Velocity Interferometer System for Any Reflector (VISAR) interferometers have been fielded to measure shock velocities, breakout times, and emission of targets sized from 1 to 5 millimeters. A 20-cm-diameter, fused silica triplet lens collects light at f/3 from the targets inside the 10-meter-diameter NIF vacuum chamber. VISAR recordings use a 659.5-nm probe laser. By adding a specially coated beam splitter at the interferometer table, light at wavelengths from 540 to 645 nm is split into a thermal-imaging diagnostic. Because fused silica lenses are used in the first triplet relay, the intermediate image planes for different wavelengths separate by considerable distances. A pair of corrector lenses on the interferometer table reunites these separated wavelength planes to provide a good image. Streak cameras perform all VISAR and thermal-imaging recording. Alignment techniques are discussed.