Exploration of the multiparameter space of nanosecond-laser damage growth in fused silica optics.

Historically, the rate at which laser-induced damage sites grow on the exit surface of SiO2 optics under subsequent illumination with nanosecond-laser pulses of any wavelength was believed to depend solely on laser fluence. We demonstrate here that much of the scatter in previous growth observations was due to additional parameters that were not previously known to affect growth rate, namely the temporal pulse shape and the size of a site. Furthermore, the remaining variability observed in the rate at which sites grow is well described in terms of Weibull statistics. The effects of site size and laser fluence may both be expressed orthogonally in terms of Weibull coefficients. In addition, we employ a clustering algorithm to explore the multiparameter growth space and expose average growth trends. Conversely, this analysis approach also identifies sites likely to exhibit growth rates outside the norm. The ability to identify which sites are likely to grow abnormally fast in advance of the manifestation of such behavior will significantly enhance the accuracy of predictive models over those based on average growth behaviors.