Laser damage induced by contamination particles on coated optical components

We studied the laser radiation damage of sol-gel SiO 2 film induced by surface contamination particles. Experiments were performed on a Q-switched single-longitudinal-mode Nd:YAG laser. Particles do reduce the laser-induced damage threshold (LIDT). Especially when they are located on the front surface, the LIDT is the lowest of all. Severe erosion and diffraction rings are found in the center of the substrate. We focus on the damage morphology, contaminated samples are more prone to start up the field damage and substrate damage. In order to study this phenomenon, finite-difference time-domain (FDTD) method was employed to simulate the light intensification induced by the contamination. Results show that the modulation strength of the front-surface particles is much larger. The largest modulation area induced by the front-surface particles is located within λ substrate subsurface, which is easy to induce damage initiation. Inside, the light intensity was attenuated trend after 3 λ depth stabilized. The quantization of laser damage induced by particles, can provide the basis for the detection and control of sub-surface defects.