Micron-size bubble defects in fused silica and its laser induced damage near 355 nm

In this paper, considering micro-bubble as a factor affecting the quality of optical components assembled in high-energy laser system, the behavior of small bubble inside high-temperature fused silica is investigated by two-phase flow theory. Furthermore, the effect of microbubbles as high-energy laser damage precursor is studied in detail. It is found that if micro-cracks or voids exist in fused silica during synthesis, basically spherical bubbles could be formed and hardly released. Thereafter, light intensity enhancement effect is evaluated at the initial stage of laser-induced damage. Both single and double bubbles attribute to laser energy intensification in a specific area. The Gaussian pulsed laser near 355 nm is utilized to test laser-induced damage thresholds (LIDTs), and the LIDTs of fused silica with unreleased micro-bubbles decrease from 9.7J/cm2 to ∼7.0 J/cm2. The surface damage morphologies and laser-induced material modifications due to micro-bubble are much more disastrous than those without defects. We propose that the Gaussian laser-induced damage morphologies are partitioned into three feature zones for fused silica with unreleased bubbles. The research in this paper provides underlying guidance for ameliorating the quality of fused silica and understanding laser-induced damage.