Investigation of the entrapped micro bubble defect as a high-energy laser damage precursor in fused silica optics

Irrespective of the manufacturing process, heat pretreatment, and laser repair of optics, it is possible for entrapped bubbles to form at the subsurface or in the bulk of fused silica optics installed in high-energy laser systems. The micro bubble defect may act as a precursor to high-energy laser damage. The objective of this paper is to investigate the impact of constrained bubbles with varying characteristics on light field intensity when subjected to high-energy laser irradiation. The light intensity enhancement factor was calculated to estimate the intensification of laser energy in local areas within the material, with the aim of determining the extent of laser-induced damage. The results, which reveal a wrinkle-like light field pattern modulated by the bubble, shed light into the location and mechanism of laser-induced damage. The modulation effect of an irregular bubble is more pronounced than that of a spherical bubble. The optical transmission principle of the laser beam within the material was elucidated. The results of the experiment, which utilized nanosecond pulsed ultraviolet laser in a Gaussian beam, demonstrated that the laser-induced damage thresholds of fused silica with micro-bubble defects were lower than those of pure fused silica. This paper identifies the role of the bubble as a high-energy laser damage precursor and provides a foundation for theoretical research into the high-energy laser-induced damage mechanism of optical materials.