Defect Centers Induced By Linear And Non-Linear Absorption Of UV Light In High Purity Silica

Abstract

Defect centers induced by 6.4 eV laser light in high purity silica were studied by electron spin resonance (ESR). Both Si E' centers, and non-bridging oxygen hole centers (NBOHCs) were observed. However, the E' center was the dominant defect in type III synthetic silicas (1200 ppm OH), while the NBOHC was dominant in type IV silicas (< 5 ppm OH). Formyl radicals (HCO) and hydrogen-associated centers were also observed in high-water silica. The concentrations of both Si E' centers and NBOHCs were found to increase as the square of the 6.4 eV laser power suggesting that they are induced through non-linear absorption of UV light. By contrast, we find that the HCO concentration increases linearly at low laser power, saturates, and decreases at high power. Excitons induced by the non-linear absorption of UV light are inferred to be responsible for the generation of these observed defect centers in high purity silica.