Ab initio study of linear and nonlinear optical properties of mixed tellurite-chalcogenide glasses.

We discuss the potential functionalities of a mixed tellurite-chalcogenide glass where alternate oxygen atoms in a TeO(2) vitreous network are substituted with either sulfur or selenium atoms. We calculate the microscopic linear and nonlinear polarizabilities of chains with a finite number (n) of TeOX (X = S or Se) units from ab initio quantum chemistry computations and apply rotational averaging to the results. We find that the rotationally averaged linear polarizability, α(av), increases linearly with the number of units, while the second hyper-polarizability, γ(av), grows as a power law with an exponent that changes from 1.2 to 1.9 and 2.4 when going from pure tellurite to S substitution and Se substitution, respectively. We then estimate the density of the resulting glass and local field corrections to obtain the macroscopic linear and nonlinear susceptibilities for a glass made from chains of n = 5. We find that the extra Te-S (or Te-Se) bonds in the mixed tellurite-chalcogenide system enhance the linear refractive index n(0) and the third-order susceptibility χ((3)) by factors of ∼ 1.3 (or 1.4) and ∼ 8 (or 14), respectively, over the base tellurite glasses (X = O).