Nonlinear Optical Properties In Mg-doped Stoichiometric LiTaO₃ Crystals

In this dissertation, we first use the 90/10 kniefe-edge method to measure the radius and location of focused beam from a semiconductor laser, in order to perform the Z-scan and pump-probe experiments for characterizing the nonlinear optical propertiest in Mg-doped stoichiometric LiTaO3. The third-order nonlinear optical properties are measured in several stoichiometric Mg-doped LiTaO3 crystals with different doping concentration (0.7mol%, 1.0mol%, 1.2mol% ) by the Z-scan method with a continuous-wave semiconductor laser operating the wavelength of 532 nm and an intensity level of 50 kw/cm~2. The third-order optical nonlinear refractive indexγand nonlinear absorption coefficientβare determined. In Mg doped stoichiometric crystals with Mg concentrations 1.2mol%, the absorption are saturation absorption, which is negative Mg-dopant level below 1.0mol%.The light-induced briefringence changes of the samples are measured by pump-probe method. We find that the light-induced birefringence changes are observed in nominally pure and 0.5 and 0.7 mol% MgO-doped SLT crystals, and the changes of light-induced briefringence decrease with the dopant, as well as increase with pumping intensity. In the crystals with concentration of Mg higher than 1.0 mol%, the light-induced birefringence changes are too small to detect at lower intensities than 8 MW/m2, and the changes almost increase linearly with intensities higher than 8 MW/m2.When pump beam is closed, light-induced briefringence changes vanish quickly, which shows that thermal-optic effect happen in these crystals with high concentration of Mg higher than 1.0 mol%. As a result, the photorefractive threshold in Mg-doped stoichiometric LiTaO3 is between 0.7mol% and 1.0mol%.By using the Z-scan and pump-probe methods, we investigate the nonlinear optical properties, i.e., dependence of the third-order nonlinear optical coefficients and light-induced birefringence changes on the doping concentration in the Mg-doped stoichiometric LiTaO3 crystals. The results are useful for advanced applications of this material.