Structure and nonlinear optical properties of BaO-TiO2-B2O3 glasses

The third order nonlinear optical susceptibilities χ(3) of BaO-TiO2-B2O3 glasses have been measured by the third harmonic generation (THG) method. Raman spectroscopic investigation revealed that Ti4+ ions mainly exist as 4-coordinated. It was found that the addition of TiO2 to BaO-B2O3 glass increases the χ(3) as well as the refractive index. The positive effect of the TiO2 on the χ(3) was interpreted in terms of the empty d-orbital contribution. The largest χ(3) obtained is 3.0×10-13 esu for 35BaO&middot55TiO2&middot10B2O3 glass, which is, however, only 10 times larger than that for SiO2 glass. Such a small enhancement in χ(3) is ascribed to the large fraction of 4-coordinated Ti4+ ions in BaO-TiO2-B2O3 glasses. It is concluded that, for TiO2-containing glasses, the higher χ(3) values are attained when the optical basicity is low and the amount of Ti4+ ion is large. It was found that the modified Lines' relationship between χ(3) and (n$-ω/2+2)3&middot(n$-ω/2-1)&middotEd/E 02 is adopted for this system.