Second Harmonic Generation in Sodium Tantalum Germanate Glasses by Thermal Poling

International audienceStructure, linear and nonlinear optical properties of glasses in the ternary system (90–x)GeO2–10Na2O–xTa2O5 have been investigated. These glasses exhibit a wide transparency window from 350 to 5500 nm and refractive index ranging from 1.78 to 1.93. Upon a thermal poling treatment under nitrogen atmosphere using increasing poling voltages, second harmonic generation (SHG) quantitative measurements were performed and have confirmed the electro-optical origin of the second-order optical responses; χ(2) values ranging from 0.06 to 0.3 pm/V were obtained, depending on the poling conditions and glass composition. SHG/Raman correlated microscopy measurements allowed identification of the structural changes within the poled layer and pointed out that sodium depletion led to a more connected glass network through cross-linking bonds such as Ge–O–Ge and Ta–O–Ta bonds. A deviation from a pure electro-optical second-order response is observed for the highest poling voltage. In this particular case, a linear optical birefringence and a structural χ(2) might have to be taken into account to describe accurately the polarized layer optical properties