Abstract

Although photoinduced defects in silica have been studied by linear spectroscopy and electron spin resonance for several decades,¹ disagreement remains concerning the mechanism by which sub-band-gap light generates defects. In one scenario two-photon absorption creates an exciton, whose nonradiative decay leads directly to a defect. Alternatively, energy transfer from either a photoexcited defect or an exciton to a preexisting precursor defect transforms it from a nonparamagnetic to a paramagnetic defect.² In previous experiments defects have typically been created by high-energy nanosecond excimer laser pulses (5.0, 6.4, and 7.9 eV). We report the first, to our knowledge, femtosecond time-resolved studies of the primary photophysical process of defect creation in high-purity amorphous and crystalline SiO₂.

© 1993 Optical Society of America