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Large-aperture laser-resistant mirrors are required for the construction of the National Ignition Facility, a 1.8 MJ laser. In order to fabricate the 1408 mirrors, a development program was started in 1994 to improve coating quality, manufacturing rate, and lower unit cost. New technologies and metrology tools were scaled to meter size for facilitization in 1999 at Spectra-Physics and the Laboratory of Laser Energetics at the University of Rochester. Pilot production, to fabricate 5-10% of each component, commenced in 2001 and full production rates were achieved in 2002. Coating production will be completed in 2008 with the coating of 460 m 2 of high-damage-threshold precision coatings on 100 tons of BK7 glass with yields exceeding 90%.

Studies into the functional damage thresholds of hafnia/silica thin film coatings for the NIF laser have been conducted on two different-sized substrates: 50-mm-diam test substrates and full-sized (412 x 412 mm) NIF mirror substrates. For both studies, the optics were raster scanned by Q-switched Nd:YAG lasers emitting 1064-nm light with 10- ns pulse lengths. The coatings tested were primarily high reflectors, although polarizing beam splitter and anti- reflective thin films were tested on the small substrates. Tests were performed to find the functional damage threshold: the minimum fluence at which a damaged optic degrades the performance of the NIF laser, or, experimentally, the minimum fluence at which a damaged site begins to grow. Thus, the concern is with finding not only the fluence that caused a pit (for example) but also the fluence at which that pit begins to grow with subsequent laser shots. After a site begins a growth phase, the growth rate is measured as a function of fluence. This provides some information for predicting the optic lifetime for given operating limits of the laser.