The National Ignition Facility (NIF) requested an optical diagnostic for measuring shock velocities, shock breakout times, and shock emission of objects with sizes of 1 to 10 mm. For the polar port of the target chamber, an 8-inch triplet lens collects light at f/3 inside a 30-foot-diameter vacuum chamber and uses an optical relay to send the image into two interferometers located at a distance of 160 feet. Light propagates through a VISAR (Velocity Interferometry System for Any Reflector) interferometer employing a Mach-Zehnder configuration. After exiting the interferometers the images are recorded, both by streak cameras and CCD gated imagers. Discrete magnification changes are accomplished by swapping out optical elements. Large dove prisms are used to rotate the image to align a selected region of the object with the slits of the streak cameras. Unique mounting structures are required to remotely control the alignment of the optical axis. Finite Element Analysis (FEA) was performed on all mounting structures. The first 8-inch triplet can be no closer than 500 mm from the target chamber center and is protected by a blast window that has to be replaced after every event. The first several lens groups have to be fused silica for radiation resistance. A frequency-doubled Nd:YAG laser, operating at 659.5 nm, is used to illuminate the moving object. The VISAR laser wavelength had to be different than the first, second, and third harmonics of the NIF drive lasers.

Date Published: 3 November 2003
PDF: 12 pages
Proc. SPIE 5173, Current Developments in Lens Design and Optical Engineering IV, 517304 (3 November 2003); doi: 10.1117/12.506774

Published in SPIE Proceedings Vol. 5173:
Current Developments in Lens Design and Optical Engineering IV
Pantazis Z. Mouroulis; Warren J. Smith; R. Barry Johnson, Editor(s)