Time-resolved holographic study of laser-induced fatigue in bulk of sapphire and fused silica

Abstract

In this work, the fatigue effect caused by multi-pulse laser irradiation in bulk of transparent optical medium for ultrashort pulses is investigated. Time-resolved digital holography is used as a sensitive tool for quantifying changes in material response below single-shot damage threshold. In case of two investigated fused quartz samples the survivable dose is limited by increase in the yield of free electrons and self-trapped exciton densities with number of expositions prior to damage formation. Meanwhile, no change was detected in free electron plasma for sapphire before multi-pulse damage which lead to nondeterministic damage. It was estimated that optical damage could form bellow critical plasma density for all samples. The data on low energy irradiation and damage morphology suggest a strong contribution from defects to the initiation of multi-pulse optical damage in bulk media.