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

Abstract

For the aggressive fluence requirements of the NIF laser, some level of laser-induced damage to the large (40x40 cm) 35 1 nm final optics is 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 (NIP has a flattop beam). The defect density is found to vary as a power of the fluence (Weibull distribution).

Investigation of annealing effects on the laser-induced damage threshold of amorphous Ta2O5 films

“…Up to now, the only model used to interpret damage statistics in the nanosecond laser pulse regime is based on a physical assumption that the damage site is linked to the presence of at least one defect [23,24]. As the defect has a larger absorbance index than the film around, it is more liable to absorb laser energy.…”

Laser-induced damage of intrinsic and extrinsic defects by picosecond pulses on multilayer dielectric coatings for petawatt-class lasers

“…If damage is driven by defects (extrinsic), the fluence at which damage onset is observed will depend on the test area. 14,15 This effect can be easily understood, if we consider a sparse distribution of defects on the surface of an optic; the probability of encountering a defect will depend on the test area, i.e., higher for large-area beams leading to a perceived lower damage threshold compared to that obtained using a smaller area beam. The standard damage test methodologies (1/1, S/1, and R/1) using a small-area beam are often used due to easy access to table-top lasers and the simplicity of the tests.…”

Initiation, growth, and mitigation of UV-laser-induced damage in fused silica

“…A more useful characteristic, which can be assumed independent of spot size and is a function of the material only is the density of defects damaged at given fluence n(F) [5]. Typically, the dependence on fluence is a power law where k is typically ~8-12.…”