非線性材料鈦酸鍶鋇之光學性質研究

Abstract

本文主旨在研究鈦酸鍶鋇的光學特性，利用溶膠-凝膠方法製備一系列不同成分比例的鈦酸鍶鋇（BST）粉末材料，經由x-光繞射數據計算其晶格常數，以橢圓儀量測折射率和改良式Kurtz粉末二倍頻量測有效倍頻係數，並且與理論值結果比較。經由有效倍頻係數的量測，我們可以說明在室溫時，不同成份的BaxSr1-xTiO3(BST)，在x為0.7∼0.8之間，會發生結構的相變，使其由對稱的立方晶相轉變為非對稱的正方晶相，造成z軸晶格常數變量( )、有效倍頻係數(deff)、同調長度( )和倍頻強度(I2w)有明顯的改變，此與X-ray繞射計算結果預測相符。此外，當x≧0.8時，具有非對稱的正方結構，因此有較高的的有效倍頻係數（≧4.8），為良好的非線性光學材料。

The objective of this thesis is to study the optical properties of various ratios of Ba/(Ba+Sr) BaxSr1-xTiO3 (BST) powders. The BST powders were prepared by the sol-gel method. Their lattice constant were calculated from x-ray diffraction analysis data, and the refractive index were measured by the ellipsometer . By using the modified Kurtz method to measure the effective second harmonic generation coefficients of powder materials, and together with x-ray data ,we find that BST microcrystalls have structural phase transition at room temperature when x is from 0.7 to 0.8. The structural change from centrosymmetric cubic phase to non-centrosymmetric tetragonal phase due to increasing lattice constant along z-axis, leads to the abrupt change of the effective second harmonic generation coefficients, coherence length factor and second harmonic generation intensity. The results agree well with the x-ray diffraction calculation. Furthermore, the experimental results show that the BST is a good nonlinear optical material whose effective second harmonic generation coefficients is larger 4.8 times larger than that of BBO when the Ba composition is greater than 0.8.