The Interaction Mechanisms Between The Impurity And The Intrinsic Defect In Fused Silica

Fused silica is a kind of laser lens material widely used in the High-power laser systems. Laser induced damage generated by laser irradiation is an important issue in the institution of the fused silica, which will decline the material's optical transparency. All kinds of particle groups introduced in the pickling process would inevitably interact with fused silica, affecting the performance of the fused silica devices. The intrinsic point defects of fused silica and impurity particles have important influence on the properties of fused silica. Although the related research has been underway for many years, all of these work basically separated the intrinsic point defects and impurity particles. There are not a subject systemically studying the interaction mechanism between the impurity particles and point defects yet. Based on the urgent need in the process of surface treatment of fused silica devices, the mechanism of metal particles and free radicals in fused silica with various intrinsic point defects as well as the nature of diffusion path and energy change are studied, which are of positive significance to eliminate the impurity particles in the process of production.The main contents of this paper are as follows:(1) Using first-principle calculations, we study the interconversion of two similar defect structures, POL and POR-E', including predicted stable structure. We use the GOWO+BSE method to study the electronic structure and optical properties of the defect. Our results not only give an insight into the structure interconversion of oxygen-excess intrinsic defects, but also explain why it is difficult to observe the absorption of the POL defect experimentally.(2) Ammonium group (NH4) is the major impurity introduced by the process of wet chemical etching for fused silica. By using first-principle calculations, we investigate the diffusion behavior of ammonium group in fused silica. We focus on the interaction mechanisms of ammonium group with four kinds of intrinsic defects (ODC(I),POL,POR-E ' ,NBOHC-E ' ),and the relevant reaction paths and energy barriers are also obtained.We make comparison about the adsorption capacities of these defects and give reasonable explanations about how the intrinsic defects influence the diffusion behavior of ammonium group.