Effect of scratch defects on photoinduced damage characteristics of fused quartz

Abstract

When a laser beam irradiates an optical material, a light standing wave field should be observed inside the optical material due to the interference between the beam reflected from the rear surface and the incident beam. If there are scratches on the surface, the incident light can be modulated and the distribution of the standing wave field inside the material is not uniform any more. Therefore, the appearance of the local enhancement of light will change the damage characteristics of optical material. To analyze the field damage characteristics of optical material with scratches, a theoretical analysis model is established. It can be used to study the damage characteristics and build a priori model of actual optical material. Fused quartz is employed as the study object, and the modulation effect of defect on light field is simulated by finite difference time domain (FDTD). Based on the electron multiplication theory, the effect of the number and the positions of scratches on the damage characteristics of fused quartz are calculated in detail. The results show that the phase modulation of the scratch will destroy the uniformity of the standing wave field when the scratch defect material is irradiated by laser. Due to the influence of the standing wave field, the maximum field intensity appears near the rear surface of the material, which explains the phenomenon that the rear surface of the material is more prone to damage points. When there are multiple scratches on the material surface, the distribution of light field is related to the number of the scratches. Specifically, the maximum field intensity increases with the number of scratches increasing. Taking fused quartz material for example, when a 10-ps pulse is incident on it, if three scratches are located on its surface, then the modulation effect on the light field is strongest, and the damage threshold is 66.1% lower than that of the ideal material. In addition, the scratch spacing also has an effect on the standing wave field and field damage characteristics of the material, and the specific effect of the interval can be analyzed directly by using the calculation model proposed in this paper.