基于数字全息干涉术的晶体畴结构检测和孔径衍射计算
文献类型：学位论文
| 作者 | 曲伟娟 |
| 学位类别 | 博士 |
| 答辩日期 | 2007 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 刘立人 |
| 关键词 | 铌酸锂 数字全息干涉术 外加电场 畴反转 |
| 其他题名 | Domain structure detection in crystal by use of digital holographic interferometry and aperture diffraction |
| 中文摘要 | Grilli等人提出利用数字全息干涉术检测LiNbO3晶体内的畴反转极化过程，并利用这种方法实现了内电场的检测与分析。这种无接触、无破坏的检测方法被证明在晶体畴反转检测方面的应用前景非常广阔。它不但可以对晶体的畴反转过程进行准实时观测，还可以对晶体中的畴结构进行量值上的测量与分析。Grilli等人应用于晶体畴反转测量的数字全息再现方案是菲涅耳变换法，该再现方法以标量衍射理论的菲涅耳近似为基础，存在分辨能力低与易受到噪音干扰等方面的问题。在改进数字全息图的记录方式与再现方法的基础上我们对铌酸锂晶体中的畴反转过程和畴结构进行的实验测量和数值计算。在平面波的角谱理论的基础上我们实现了数字全息图的数值再现和孔径衍射场在传播轴方向上的分布计算。论文一方面在总结晶体畴反转检测方法的基础上，论述了采用角谱后向传输重建算法重建物场，利用数字全息干涉术对晶体结构进行测量和检测的具体方法，为铁电晶体畴反转的观察和检测提供了一种经济有效的检测手段。通过对新型掺杂铌酸锂晶体和同成分铌酸锂晶体中的畴反转特性的深入研究，得到了一些创新性的实验结果和结论。具体体现在对掺钌铌酸锂晶体的线性电光系数和内电场的准确测量，及首次发现其反平行畴壁附近区域的二次电光效应；掺镁铌酸锂晶体中的畴核近似呈圆锥状穿透晶体的过程中，由于空间电荷场的重新分布，出现一个反常高的相位分布。另一方面对孔径衍射场分布进行了一系列的模拟计算，如平面光波和高斯光波经过平面斜交周期阵列（特别是六角阵列）、圆对称孔径等的衍射波场计算。论文的主要内容包括： （1）详细研究了晶体在畴反转过程中的折射率变化、掺杂晶体的线性电光系数、晶体中反平行畴壁附近的电压特性和晶体的内电场等。采用马赫-曾德干涉光路记录数字全息图，角谱后向传输算法对其进行再现，利用数字全息干涉术得到晶体发生畴反转前后的相位延迟分布信息。在分析该相位延迟分布信息的基础上得出掺钌铌酸锂晶体的线性电光系数13= 9.110-12m/V，掺镁铌酸锂晶体的线性电光系数13= 9.610-12 m/V。晶体中反平行畴壁附近的反转特性与其他区域的反转特性有较大差异，随外加线性电场的变化或存在二次电光效应。掺钌铌酸锂晶体内部极化方向不同时存在的内电场值约为-0.72kV/mm，该内电场作用于0.5mm厚的晶体会使其反平行畴结构表面产生2.73nm的表面差。利用该方法对晶体畴反转进行测量可达到的横向分辨能力约为9m，纵向检测精度约为±0.075rad。 （2）详细研究了铌酸锂晶体内的成核现象和畴核生长过程。采用马赫-曾德显微干涉光路记录数字全息图，傅立叶分析算法对其进行再现，利用数字全息干涉术得到晶体内畴核生长过程的相位延迟分布信息。在分析该相位延迟分布信息的基础上得出同成分铌酸锂晶体在低电场下的成核过程和畴核生长的位置比较稳定，掺镁铌酸锂晶体内的成核或与镁离子的分布浓度有关，在镁离子浓度较重的区域，多核合并比较明显，单核呈圆锥状穿透晶体的过程中，由于电荷场的重新分布，出现一个反常高的相位分布。利用该方法对晶体畴反转进行测量可达到的横向分辨能力约为0.9m。 （3）在平面波的角谱理论的基础上对自由空间中的光束传播进行了一系列的理论模拟计算。推导出平面斜交周期阵列的泰伯距离及其分数泰伯像平面的相位分布公式, 以60。斜周期菱形阵列为例，对斜周期阵列的自成像效应和正交周期阵列的自成像效应进行了比较；模拟研究了平面六角阵列的泰伯像与分数泰伯像，并提出基于分数泰伯效应的平面六角阵列照明，模拟计算出实现占空比为1/12的平面六角阵列照明的相位板分布；模拟计算了高斯光波通过不同口径大小的圆孔和圆环孔后的衍射场分布。 |
| 英文摘要 | Recently, Grilli et al. propose in situ visualization and monitoring of the domain inversion process in LiNbO3 crystal by use of digital holographic interferometry, and they have used this technique to realize measurement and analysis of the internal field of the crystal. It is noncontact and nondestructive and has been demonstrated to be a prospective method for measurement of domain inversion in ferroelectric crystal. The method can not only visurelize the domain inversion in real-time but also quantitatively measure and analyze the domain structure. The reconstruction method used by Grilli et al. is the Fresnel transform algorithm, which is based on the Fresnel approximation of the scalar diffraction theory and has the problem of lower lateral resolution and easily be disturbed by the noise. In the thesis, we present the experimental studies and numerical calculations of the domain inversion process and the domain structure in LiNbO3 crystal by use of digital holographic interferometry with an improved reconstruction method. Based on the theory of angular spectrum of the plane wave, we have finished the reconstruction of the digital hologram and the numerical calculation of the aperture diffraction along the propagation axis. On the one hand, we summarized all the methods used to visualize and detect the polarization reversal in the ferroelectric crystal. Based on that, we give a clear description how to detect the domain inversion by using of the digital holographic interferometry with the angular spectrum backward propagation method. It has been proved to be an economical and effective method. Through the further investigation of the new doped LiNbO3 crystal and the congruent LiNbO3 crystal, we get some creative experimental results and conclusions. On the other hand, we numerically calculate the plane wavefront and the Guassian wavefront diffracted by apertures such as the two-dimensional array with arbitrary shape and symmetry (especially the hexagonal array) , circular aperture and so on. The thesis is divided into three blocks: (1) Detailed studieds of the variation of the refractive index in the process of domain inversion. The linear electro-optic coefficient of different doped crystal sample, the unique property of the region across the antiparallel domain wall and the internal field are presented. The crystal wafers are placed into one arm of a Mach-Zehnder-type interferometer to record a series of holograms. Making use of the angular spectrum backward propagation algorithm, we reconstruct the optical wave field in the crystal plane. The extracted phase difference from the reconstructed optical wave field is a well linear function of the applied external voltage. We deduce that the linear electro-optic coefficient of the detected RuO2:LiNbO3 crystal sample is 9.110-12m/V and the linear electro-optic coefficient of the detected MgO:LiNbO3 crystal sample is 9.610-12m/V. This tells us that the different dopants really affected the linear electro-optic coefficient of the crystal. An unexpected phase-contrast across the antiparallel domain wall is also observed and the influence of the applied external voltage on it is studied in detail in the RuO2:LiNbO3 crystal sample. There maybe a nonlinear effect in this region. Also its built-in internal field is quantitatively measured as 0.72kV/mm.If applied on a 0.5mm crystal thickness it expects 2.73nm surface height difference between the antiparallel domains. The lateral resolution of the using technique is 9m, its axial resolution is estimated as ±0.075rad. (2) Detailed studies of the domain nucleation and the growth of the domain nucleus in LiNbO3 and MgO: LiNbO3 crystals are presented. The crystal wafers are placed into one arm of a Mach-Zehnder-type microscopic interferometer to record a series of image holograms. Making use of the Fourier analysis algorithm, we reconstruct the optical wave field. The extracted phase differences from the reconstructed optical wave field clearly indicate the steady location of the domain nucleation and the growth of the domain nucleus in an electric field lower than the coercive field in the congruent LiNbO3 crystal. The domain nucleation and the growth of the domain nucleus in the congruent MgO: LiNbO3 crystals is influenced by the distribution of the Mg2+. In the regions where exist a high density of Mg2+, many domain nucleus appear and merge into one domain with hexagonal shape. An unexpected peak phase is observed in the beginning of the domain nucleation and it is decreased as the spreading of the domain nucleus. The existence of the nucleus changes the moving speed of the domain wall by pinning it for 3 seconds. The lateral resolution of the using technique is 9m. (3) Based on the angular spectrum of plane waves, a series of simulations of the free propagation of the light wavefront are presented. In this segment, we theoretically proved the fractional self-imaging effect of the two-dimensional array with arbitrary shape and symmetry, and then got a general equation to calculate the phase of the fractional Talbot image of the two-dimensional array. As an example, we numerically evaluate the intensity distribution of 60。skewed periodic array in different fractional Talbot planes using Matlab. A comparison of it with the orthogonal periodic structure is given. A phase plate based on the fractional Talbot effect that converts a single expanded laser beam into a regular hexagonal array of uniformly illuminated apertures with virtually 100% efficiency is presented. The uniform hexagonal array illumination with a fill factor of 1/12 is demonstrated by the computer simulation. The numerical simulation of the wavefront diffracted by apertures with circular symmetry is realized. The on-axial irradiance distributions of plane wavefront and Gauss wavefront diffracted by the circular aperture have been calculated. Comparisons of the simulation results with the analytical results and the experimental results tell us that it is a feasible method to calculate the diffraction of apertures. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15431]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 曲伟娟. 基于数字全息干涉术的晶体畴结构检测和孔径衍射计算[D]. 中国科学院上海光学精密机械研究所. 2007. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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