Thermal poling of glass modified by gamma radiation

Flame-fused type-II silica glass and synthetic type III silica glass were exposed to gamma radiation and then thermally poled. Second-harmonic generation (SHG) is reduced by several orders of magnitude in Suprasil glass for doses higher than 100 kGy and in Herasil glass for doses higher than a few MGy. In Herasil glass, however, SHG is unchanged for doses lower than about one MGy. In the latter case, Maker fringe measurements show that, like in the poled pristine glass, the second-order nonlinearity is located in a thin layer beneath the anodic surface. On the other hand, in the former case, Maker fringe measurements reveal the existence of weak bulk nonlinearity. This unexpected result suggests that dipole orientation takes place in the glass modified by gamma radiation.