Nonlinear optical properties and glass structure for MO–Nb2O5–TeO2 (M = Zn, Mg, Ca, Sr, Ba) glasses
Résumé
The third-order nonlinear optical susceptibilities v(3) of tellurite(TeO2)-based ternary glasses of MO–Nb2O5–TeO2 (M = Zn, Mg, Ca, Sr, Ba) were investigated by Z-scan measurement using Ti:Sapphire femtosecond laser pulses. The relationship between the nonlinear optical properties and the glass structures estimated by Raman spectroscopy was discussed. The nonlinear susceptibilities v(3) of these tellurite glasses increased as the stretching Raman band of TeIV–Oax in TeO4 (trigonal bipyramids (tbp), the roman superscript denotes the coordination number) increased, while the stretching band of TeIII–O in TeO3 (trigonal pyramid (tp)) decreased. This indicates that the amount of TeO4 (tbp) units was deeply related to the value of v(3), which was consistent with the theoretical calculation of higher hyperpolarizabilities of TeO4 than TeO3 unit. It was also found that higher v(3) was obtained with decreasing TeIV– eqOax–TeIV Raman band, indicating that when divalent cations (M2+) was doped in Nb2O5–TeO2 binary network system the cleavage of TeIV–eqOax–TeIV chain structure necessarily occurred but the terminations of –TeIV–eqO M2+ O–NbVI–Oax–TeIV–, which importantly stabilized TeO4 units even in the presence of the network modifier M2+, were more preferentially induced with an assist of NbO6 octahedron than –TeIV–eqO M2+ O = TeIII–O–.