Crystallization and optical nonlinearity in GeO2–SiO2 glass poled with ArF excimer-laser irradiation

We report on crystallization and second- and third-order optical nonlinearities of GeO2–SiO2 glass poled with ArF laser irradiation. With laser power and 100 mJ/cm2/pulse, the treatment generates crystallites in the glass, provided that the poling field strength is greater than 0.5×105 V/cm. Its crystal structure is possibly the cristobalite phase of the Ge–Si–O system. A large coefficient of second-harmonic generation (SHG), d33, is induced in the glass with the crystallite generation, and its value is comparable to d22 of LiNbO3. Moreover, the third-order optical susceptibility χ(3) increases by a factor of approximately 15 compared to that of glass without the crystallites. Even after the d33 coefficient decays out, the crystallites and χ(3) are retained. The result suggests that the large SHG in the glass is not induced from inert second-order nonlinearity of the crystallites, but the main origin of the induction is the associated effective second-order nonlinearity with the formation of the space-cha...