Structural defects in ultra-low laser absorption fused silica

Abstract

Fused silica is used as windows or lens in high power laser system. Slight laser absorption in it may results in huge damage caused by thermal effects. In order to reduce the bulk optical absorption in fused silica, mechanism of laser absorption in fused silica was studied from the perspective of structural defects. Ultra-purity fused silica was synthesized by high frequency plasma chemical vapor deposition (PCVD) process. Characteristics of structural defects includes hydroxyl, metal impurities, oxygen vacancy, bubbles and invisible stripe were studied by transmission spectrum, infrared reflection spectrum, stress birefringence, confocal microscope and impurity analyses. Formation mechanism of structural defects in fused silica was analyzed according to deposition process and vitrifying mechanism of silica. And influence of structural defects on bulk optical absorption was analyzed. By controlling structural defects, ultra-low laser absorption fused silica was synthesized by PCVD process.