Glass structure and optical nonlinearities in thallium(I) tellurium(IV) oxide glasses

The relationships between structure and nonlinear optical response at 1.5 mu m in thallium(I) tellurite glasses are investigated, Usually in tellurite glasses, the introduction of a modifier ion changes the basic structural TeO4 disphenoid entity progressively into a TeO3 trigonal bipyramid via an intermediate TeO3+1 polyhedron. This evolution leads to a decrease of the nonlinear refractive index n(2). Nevertheless, if a modifier ion such as Tl+ also has an ns(2) lone electron pair, n(2) increases although the same structural evolution is observed around the tellurium atoms, This result is related to the hyperpolarizability of the thallium oxygen entities, which has been evidenced by the structural study of both thallium(I) tellurite crystals and glasses of the same compositions. With this solid state chemistry approach, the highest non-linear refractive index measured at 1.5 mu m (n(2) = 9.10(-19) m(2)/W) and reported in oxide glasses has been obtained. (C) 1999 Academic Press.