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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.

We have developed and are continuing to refine semi-automated technology for the detection and inspection of surface and bulk defects and damage in large laser optics Different manifestations of the DAMOCLES system (Damage and Artifact Mapping Of Coherent-Laser-Exposed Substrates) provide an effective and economical means of being able to detect, map and characterize surface and bulk defects which may become precursors of massive damage in optics when subjected to high-fluence laser irradiation Subsequent morphology and evolution of damage due to laser irradiation can be tracked efficiently The strength of the Damocles system is that it allows for immediate visual observation of defects in an entire optic, which can range up to l-meter dimensions, while also being able to provide digital map and magnified images of the defects with resolutions better than 5 µm.

S. Schwartz, R. T. Jennings, J. F. Kimmons, R. P. Mouser, C. L. WeinzapfelM. R. Kozlowski, C. J. Stolz, J. H. CampbellLawrence Livermore National LaboratoryP.O. Box 808, L-496Livermore, CA 9455 1-0808ABSTRACTA sizable laser damage metrology effortis required as part of optics production and installation for the 192 beam Nationalignition Facility (NIF) laser. The large quantities, high damage thresholds, and large apertures of polished and coated opticsnecessitates vendor-based metrology equipment to assure component quality during production. This equipment must beoptimized to provide the required information as rapidly as possible with limited operator experience. The damage metrologytools include: I) platinum inclusion damage test systems for laser amplifier slabs, 2) laser conditioning stations for mirrorsand polarizers, and 3) mapping and damage testing stations for UV transmissive optics. Each system includes a commercialNd:YAG laser, a translation stage for the optics, and diagnostics to evaluate damage. The scanning parameters, opticallayout, and diagnostics vary with the test fluences required and the damage morphologies expected. This paper describes thetechnical objectives and milestones involved in fulfilling these metrology requirements at multiple vendors.KEYWORD LISTLaser damage, laser damage metrology, NIF metrology, National Ignition Facility, large area conditioning, laser glass

The Laser Program at LLNL has developed automated facilities for damage testing optics up to 1 meter in diameter. The systems were developed to characterize the statistical distribution of localized damage performance across large-aperture National Ignition Facility optics. Full aperture testing is a key component of the quality assurance program for several of the optical components. The primary damage testing methods used are R:1 mapping and raster scanning. Automation of these test methods was required to meet the optics manufacturing schedule. The automated activities include control and diagnosis of the damage-test laser beam as well as detection and characterization of damage events.