Identification of defects associated with second-order optical nonlinearity in thermally poled high-purity silica glasses

A large second-order optical nonlinearity has been found to be generated in various kinds of silica glasses in which an even-order optical nonlinearit y is inherently prohibited. Thermal poling is a typical procedure to genera te such a second-order optical nonlinearity, but a mechanism behind the gen eration is not elucidated completely. It should be pointed out, however, th at the nonlinearity was not added to high-purity silica glasses by poling. In this article, we show that the nonlinearity is generated in high-purity silica glasses irradiated by a KrF excimer laser before poling. We also sho w that the laser pulses erase the nonlinearity induced in the glasses. In a ddition to the laser irradiation effects on the generation and erasure, opt ical absorption and luminescence spectra in the glasses show that point def ects of =Si-O- play a key role for the nonlinearity. (C) 2001 American Inst itute of Physics.