Advances in subsurface defect detection technologies for fused silica optical elements

Fused silica is extensively utilized as a crucial optical material owing to its exceptional optical properties and thermal stability in diverse sectors such as semiconductor technology, astronomy, and military applications. However, the inherent hardness and brittleness of fused silica led to the occurrence of sub-surface defects during machining and manufacturing processes. These defects, comprising micro-cracks, scratches, and pits, remain concealed beneath the material's surface or within the post-polishing re-deposition layer, eluding conventional detection methods. Nonetheless, they exert a substantial influence on the performance of optical components, particularly in high-power laser systems. Sub-surface defects markedly diminish the laser-induced damage threshold of optical components by reducing optical transmittance, escalating scattering loss, and potentially compromising mechanical strength. This paper investigates the current theoretical frameworks and research trajectories in this domain. It delineates the application context and imperatives for fused silica optical components, elucidates the principles and ramifications of sub-surface defects, and provides a succinct overview of the contemporary research status and applicability spectrum of various damage and non-damage defect detection technologies. Furthermore, it synthesizes extant detection methodologies, delineates the merits and demerits of distinct defect detection approaches, and delineates avenues for future development and research.