Three dimensional numerical simulation of modulation by scratches on fused silica surface

Abstract

The scratches generated during optical manufacturing influence the LIDT (laser induced damage threshold) performance of fused silica components. In order to get a better understanding of this influence, the three dimensional FDTD (finite-difference time-domain) simulation is employed to study the light field distribution of scratches under laser irradiation and the relationship between the location, geometry and distribution of scratches and LIEF (light intensity enhancement factor). The results show that scratches located on the exit surface are more likely to induce damage. The geometric size of a single scratch greatly affects its LIEF value. The LIEF of a scratch with the same geometry increases as the width increases. While if the width of the scratch is given, its LIEF increases firstly, then decreases, eventually it tends to be stable as the geometry varies. For Hertzian scratches, the LIEF of adjacent scratches is larger than that of a single scratch due to the superposition of field strength; when the distance between Hertzian scratches becomes farther, the superposition of field strength gradually weakens, and finally reaches the same level as that of a single scratch. These results can help controlling the scratches to improve the quality of optical components.