Extrapolation of damage test data to predict performance of large-area NIF optics at 355 nm

摘要

For the aggressive fluence requirements of the NIF laser, some level of laser-induced damage to the large (40 * 40 cm) 351 nm final optics in inevitable. Planning and utilization of NIF therefore requires reliable prediction of the functional degradation of the final optics. Laser damage tests are typically carried out with Gaussian beams on relatively small test areas. The tests yield a damage probability vs. energy fluence relation. These damage probabilities are shown to depend on both the beam fluence distribution and the size of area tested. Thus, some analysis is necessary in order to use these test results to determine expected damage levels for large aperture optics. We present a statistical approach which interprets the damage probability in terms of an underlying intrinsic surface density of damaging defects. This allows extrapolation of test results to different sized areas and different beam shapes (NIF has a flattop beam). The defect density is found to vary as a power of the fluence (Weibull distribution).