Damage initiation and growth in multilayer dielectric films at 1064nm

The lifetime of optics in high power laser system is typically limited by both laser-initiated damage and the subsequent growth of laser-initiated damage sites. The single- and multiple-shot irradiations for HfO2/SiO2 high-reflective coatings, deposited from hafnia and silica at 1064nm in nanosecond were investigated. It was found that when shot number increased, the possibility of damage growth increased as well. The relationship between field distribution and damage morphologies and inner structures was discussed to reveal mechanism of damage initiation. Additionally, the damage morphologies under different laser fluence and shot numbers were characterized to discuss the damage growth mechanism upon subsequent pulses. The tested results illustrated the absorbers which induced damages were random distribution, and the second highest peak of field intensity at the fourth interface was high enough to induce the micron-sized damage pits. It was found that defect density had a significant impact on the damage site whether growing or not upon subsequent laser pulses. Additionally, the growth resulted in delamination, and in turn delamination accelerated damage growth, finally the catastrophic damage happened