Investigation Of The Optical Nonlinearities In The Tellurite Glasses

The enhanced nonlinear optical has attracted much interest with novel applications in optoelectronics, optical switchers and limiters, as well as in optical memory, and nonlinear spectroscopy. The object of this work was to develop a kind of heavy metal tellurite glasses, which may be used for application of the nonlinear optical materials. In this thesis, analysis had been made about the relationships of composition, properties and optical nonlinearity within the heavy metal tellurite glasses.The purpose and significance of the dissertation are summed up in Chapter one. Following the overview the development of investigation on optical nonlinearity, the latest development and application of the tellurium oxide-based glasses is reviewed. The theories of the third order optical nonlinearity are also included.In Chapter two, the extrapolation to obtain the optical band gap and Urbach energy are introduced. The value of the optical band gap can be derived from the plot of (α(ω)?ω)1/2 against photon energy ?ωand (α(ω)?ω)2 against photon energy ?ωin eV by extrapolating the linear portions to zero absorption, and Urbach energy is calculated from the slope of the straight line in plot of ln(α) vs. photon energy ?ωin eV. The third-order nonlinear optical properties was measured by z-methodThermal stability and third-order nonlinear optical properties of TeO2-Bi2O3-TiO2 glasses were studied in Chapter three. Direct allowed transition (Eopt), indirect allowed transition, and Urbach energy (ΔE) of samples were calculated according to classical Tauc equation. The relationships between thermal stability and glass composition were discussed firstly. The third-order nonlinear optical properties were measured by z-method. The effects of content of TiO2 and Bi2O3 on metallization criterion, optical band gap (Eopt), refractive indices and third-order nonlinear refractive index of glass samples were also discussed. The results show that the TeO2-Bi2O3-TiO2 glass system has good stability. The refractive index and third-order nonlinear refractive index of the glasses increase with tendency for small optical band gap and metallization criterion.In the fourth Chapter, the formation range of ternary TeO2–Nb2O5–Bi2O3 glass system was studied. The TeO2–Nb2O5–Bi2O3 glass system has small domain. The optical properties (refractive index, the third-order nonlinear optical properties et al) were investigated. The largest refractive index value 2.1927 at 632.8 nm was obtained for 75TeO2–10Nb2O5–15Bi2O3 glass. The third-order nonlinear optical properties were measured by z-method. The refractive index and third-order nonlinear refractive index of the glasses increase with increasing molar volume, tendency for small energy band gap, optical band gap and metallization criterion.In Chapter five, crystallization kinetics of (85-x) TeO2–10Bi2O3–5Nb2O5–xTiO2 (where x=2, 4, 6 mol %) glasses were studied. The activation energy for crystallization (E), the activation energy for glass transition (Et) and the Avrami parameter (n) are evaluated. The kinetic parameters indicated changes accompanied with TiO2 additions, implying that the TiO2 is an effective nucleating agent for promoting the crystallization of TeO2–Bi2O3–Nb2O5 glass. The Avrami parameter was used to demonstrate the three-dimensional growth of crystals in the glass matrices. The main crystal phase was Bi2TeO5 by the treatment. The grain size of Bi2TeO5 increased obviously with high heat treatment temperature.At the last, all results of present work are outlined, and some investigations which should be carried out in the future are also discussed.