【作者】 田浩；

【导师】 周忠祥；

【作者基本信息】 哈尔滨工业大学 ， 光学， 2008， 博士

【摘要】 近十几年来,顺电相电光晶体由于其在光纤通讯器件、光学信息处理等方面的应用而被广泛研究。其中,顺电相钽铌酸钾锂晶体(K1-yLiyTa1-xNbxO3,KLTN)在外加电场作用下可以大幅度提升其光折变性能,具有衍射效率高、电场响应速度快(几个纳秒)、二次电光系数极大等优点,被认为是用作电控全息器件的最佳材料。但生长高光学质量的KLTN晶体十分困难,严重阻碍了其物理性质和应用的研究。本论文对顺电相KLTN晶体及其掺杂晶体的生长、电光及电控光折变性质做了系统的理论和实验研究。采用顶部籽晶助溶剂法生长了多种组分及掺杂的KLTN晶体。研究了适宜晶体生长的温场和工艺条件,生长态晶体组分均匀、无开裂、无生长条纹,等径部分的尺寸达到15×15×20mm3。在生长KLTN晶体的基础上,用钠代替锂元素,进行了新晶体钽铌酸钾钠的生长探索,依据固-液界面的扩散理论,讨论了部分钽铌酸钾钠晶体显兰色的原因。系统地研究了KLTN晶体的基本物理性质。使用X射线衍射技术,分析了不同组分KLTN晶体在室温下的结构,研究了其晶格参数随组分变化的规律。利用电桥法研究了KLTN晶体的介电性质,其介电系数随温度的变化遵守Curie-Weiss定律。依此规律判断了晶体的居里温度,给出了居里温度随组分变化的规律。利用最小偏向角法,精确地测量了KLTN晶体的折射率,得到了KLTN晶体折射率色散的塞尔迈耶尔方程。采用紫外-可见光-近红外光栅光谱仪测量了KLTN晶体的光学透过性能,确定了晶体的透光范围。根据KLTN晶体紫外吸收边的位置,计算了晶体的禁带宽度,并研究了掺杂过渡元素对晶体的禁带宽度的影响。使用折射率椭球法,计算了不同外加电场作用时顺电相KLTN晶体的折射率变化。分析了用Mach-Zehnder干涉法测量晶体电光系数的原理及影响实验精度的因素。设计、搭建了自动扫描Mach-Zehnder电光系数测量系统,研究了KLTN晶体的电光性质。发现KLTN晶体在居里温度附近具有很大的二次电光系数s1 1,其数值比其它电光材料高1-2个量级。根据DiDomenico和Wemple的理论,解释了KLTN晶体电光系数随温度变化的原因,并计算了晶体的极光系数。发现在误差范围内KLTN晶体的极光系数是个常量,不随温度变化。依据光折变效应的带输运模型,结合晶体的物性参量,模拟了顺电相KLTN晶体中的空间电荷场。研究了空间电荷场随晶体的物性参数、外加电场及光栅间距等因素变化的规律。讨论了对称透射二波耦合光路配置下,有外加电场作用时,顺电相KLTN晶体内相位光栅的衍射性质,给出了二波耦合增益系数及光栅衍射效率的表达式。采用二波耦合的方法,系统的研究了掺杂过渡元素对KLTN晶体光折变性能的影响。首次研究了顺电相单掺锰、铁KLTN晶体的光折变性质,由二波耦合能量转移的方向,确定了晶体的光激发载流子类型。与传统的掺铜KLTN相比,单掺锰、铁的KLTN晶体具有更高的衍射效率,更快的光折变响应时间以及更高的光折变灵敏度。尤其是掺锰的KLTN晶体,是一种很有前途的电控光折变晶体。更多还原

【Abstract】 In recent years, paraelectric electro-optic crystals have attracted great attentions due to their potential applications in optical communication and optical information processing. Potassium lithium tantalate niobate (K1-yLiyTa1-xNbxO3, KLTN) has been considered as the best material for electroholographic applications. It exhibits enhanced photorefractive properties under external electric field, for combining the advantages of high diffraction efficiency, fast electro-optic response time (about 7 ns) and very large Kerr coefficients. However, the research on the physical properties and applications of KLTN has been hindered by the difficulty on growing high optical quality crystals. In this thesis, we investigated the growth, electro-optic and voltage controlled photorefractive properties of KLTN theoretically and experimentally.The top seed solution growth method was reviewed. The crystal growth system was designed and constructed according to the habits of crystal growth. The optimal growth procedure was investigated, and crystals with several compositions and dopant types were obtained. The crystals were with high composition uniformity, and no crack and striation was observed. The size of the as-grown crystal is up to 15×15×20 mm3. Basing on the experience of growing KLTN, we developed a new crystal sodium lithium tantalate niobate by substituting Na for Li. A solid/liquid interface diffusion model was introduced to explain the experimental results that some sodium lithium tantalate niobate crystals were blue.The physical properties of KLTN were investigated in detail. The structures of KLTN crystals were studied by using X-ray powder diffraction method. The crystals’lattice parameters were studied as a function of crystal composition. The dielectric coefficient of KLTN was studied; it changes with various temperatures obeying the Curie-Weiss law. The Curie temperatures of KLTN crystals were determined according to this law, and the relation between Curie temperature and crystal composition was obtained. The refractive indices of KLTN were measured accurately by the minimum deviation method. The Sellmeier’s equation of refractive indices for KLTN was obtained in terms of least-squares fit. The optical transmission properties were investigated by a UV-Visible-NIR spectrometer, the absorption spectra of pure and doped KLTN were determined. Energy band gap of the crystals were calculated according to the crystals’ultraviolet absorbing edge.The refractive index changes under different external fields were calculated by using index ellipsoid. An auto scan Mach-Zehnder interferometer has been designed and built for measuring the quadratic electro-optic (QEO) properties of paraelectric KLTN. KLTN has large QEO coefficient s1 1 which is two orders higher than that of the other electro-optic materials. The reason of that QEO coefficient of KLTN changed with temperatures was explained by using the theory proposed by DiDomenico and Wemple. The polarization-optic coefficients of KLTN were calculated, and they didn’t change with temperature within the experimental errors.The space-charge field of paraelectric KLTN was simulated using band transport model. The influence of the external field and grating period on the space-charge field was discussed. The diffraction behavior of volume phase grating in paraelectric KLTN was investigated under co-directional two-wave coupling configuration. The expression of two-wave coupling gain coefficient and diffraction efficiency was derived.The influence of transition metal dopant on photorefractive properties of KLTN was investigated using the two-wave mixing technique. The photorefractive properties of Mn doped and Fe doped KLTN were demonstrated for the first time, the dominant charge carrier was identified from the direction of two-wave coupling energy transfer. Comparing with the traditional Cu doped KLTN, Mn doped and Fe doped KLTN have higher diffraction efficiency, faster photorefractive response time and higher photorefractive sensitivity. Especially the Mn doped KLTN is a very promising voltage controlled photorefractive crystal.更多还原