Fate of nanosecond-pulsed 351 nm laser-ejected glass contaminants on fused silica under subsequent laser exposure

Particles generated from laser-induced damage during operation of fusion class lasers can be a source of damage precursors for neighboring optics. Such particles have been identified on the National Ignition Facility as ejecta from 1) laser damage on absorbing glass protecting the installation hardware from known stray focusing reflections in the optical path and 2) bulk damage in the borosilicate target debris shield that grows and erupts on the input surface. The dependence of the particle generation and damage initiation rate of this newly recognized damage source on laser shot parameters is not yet known, making it difficult to predict how this source would affect facility optic lifetime for projected laser operation. In this work, we measure the 351-nm fluence-dependence on the size distribution of glass particles generated by ejection from absorbing and borosilicate shield glasses onto a neighboring fused silica window exit surface. In addition, we track the fates of these ejecta and measure their probabilities of removal, damage initiation, and damage growth upon subsequent laser exposure. Thousands of particles can be ejected and deposited onto the exit surface of the fused silica window following a single pulse. Damage initiation following exposure of large borosilicate particles was observed above a fluence of 6 J/cm 2 . A laser-driven strategy to remove particles before a high fluence pulse is explored.