Modulation of incident laser by the defect site with a contamination coating on fused silica surface

Modulation of incident laser by surface defects is one of the major reasons of laser-induced damage of fused silica. In this work, the three-dimensional finite-difference time-domain calculations are employed to investigate the electrical field modulation of incident laser at 351 nm by Gaussian defect site with a contamination coating in fused silica exit surface. The effect of the dielectric constant and the thickness of the contamination coating on the electrical field distribution are discussed. The simulated results reveal that the contamination coating on defect site plays an important role in the electrical field modulation of the incident laser. The modulation becomes stronger than that without the contamination. Besides, the relationship between the electrical field modulation and the temperature of defect site surface is also studied. It is found that modulation increases with surface temperature. Meanwhile, the underlying physical mechanism is analyzed in detail.