【作者】 史婷婷；

【导师】 刘友文；

【作者基本信息】 南京航空航天大学 ， 光学， 2010， 硕士

【摘要】 本文首先利用刀口法对固体激光器聚焦的高斯光束束腰半径进行了实验测量,以利于用Z扫描和泵浦-探测实验测量镁掺杂近化学计量比钽酸锂晶体的非线性光学性质。利用Z扫描技术,以连续脉冲激光器作为光源(功率在50kw/cm2的水平,波长532nm),首次研究不同镁掺杂(0.5mol%,0.7mol%,1.0mol%,1.2mol%)近化学计量比钽酸锂晶体的三阶非线性光学性质,获得了晶体的三阶非线性折射系数与双光子吸收系数等重要数据,并发现掺镁1.2mol%钽酸锂的吸收是饱和吸收,与掺镁0.7mol%和1.0mol%钽酸锂晶体的吸收系数符号相反。利用泵浦(514 nm)探测(633 nm)技术测量晶体的光致双折射变化研究光折变效应,发现:在不掺杂,掺杂0.5mol%,0.7mol%的MgO的近化学计量比的钽酸锂晶体中,都产生了光致双折射变化,且光致双折射变化随掺杂浓度的增加而减少,随泵浦光的增大而增强;对掺杂1.0mol%MgO以上的晶体,当光强低于8MW/m~2时,几乎探测不到光致双折射变化,当光强高于8MW/m2时,随光强的增加晶体的光致双折射变化线性增加,但当关闭泵浦光时,光致双折射变化迅速消失,说明这是晶体的热光效应所致。结果表明,近化学计量比钽酸锂掺杂MgO的抗光损伤(光折变)阈值在0.7mol%和1.0mol%之间。结合Z扫描实验和光致双折射测量实验,我们研究了近化学计量比MgO掺杂钽酸锂晶体的非线性光学性质,测量的三阶非线性光学系数以及光折变效应对掺杂的依赖关系,结果对这种材料的进一步应用提供了重要的参考。更多还原

【Abstract】 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.更多还原