Crystallization and optical nonlinearity in GeO2-SiO2 glass poled with ArFexcimer-laser irradiation

We report on crystallization and second- and third-order optical nonlineari ties of GeO2-SiO2 glass poled with ArF laser irradiation. With laser power and 100 mJ/cm(2)/pulse, the treatment generates crystallites in the glass, provided that the poling field strength is greater than 0.5x10(5) V/cm. Its crystal structure is possibly the cristobalite phase of the Ge-Si-O system . A large coefficient of second-harmonic generation (SHG), d(33), is induce d in the glass with the crystallite generation, and its value is comparable to d(22) of LiNbO3. Moreover, the third-order optical susceptibility chi ( (3)) increases by a factor of approximately 15 compared to that of glass wi thout the crystallites. Even after the d(33) coefficient decays out, the cr ystallites and chi ((3)) are retained. The result suggests that the large S HG in the glass is not induced from inert second-order nonlinearity of the crystallites, but the main origin of the induction is the associated effect ive second-order nonlinearity with the formation of the space-charge field. (C) 2000 American Institute of Physics. [S0021- 8979(00)07901-4].