Nonlinear optical properties and glass structure for MO-Nb2O5-TeO2 (M = Zn, Mg, Ca, Sr, Ba) glasses

The third-order nonlinear optical susceptibilities chi((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 chi((3)) of these tellurite glasses increased as the stretching Raman band of Te-IV-O-ax in TeO4 (trigonal bipyramids (tbp), the roman superscript denotes the coordination number) increased, while the stretching band of Te-III-O in TeO3 (trigonal pyramid (tp)) decreased. This indicates that the amount of TeO4 (tbp) units was deeply related to the value of chi((3)). which was consistent with the theoretical calculation of higher hyperpolarizabilities of TeO4 than TeO3 unit. It was also found that higher chi((3)) Was obtained with decreasing Te-IV-O-eq(ax)-Te-IV Raman band, indicating that when divalent cations (M2+) was doped in Nb2O5-TeO2 binary network system the cleavage of Te-IV-O-eq(ax)-Te-IV chain structure necessarily occurred but the terminations of -Te-IV-O-eq- M2+-O-Nb-VI-O-ax-Te-IV-, 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 -Te-IV-O-eq- M2+ O = Te-III-O-. (C) 2009 Elsevier B.V. All rights reserved.