图案极化铌酸锂薄膜的制备与非线性光学应用

发布时间：2018-04-03 15:36

  本文选题：光学超晶格　切入点：图案极化铌酸锂　出处：《南京大学》2017年硕士论文

【摘要】：光学超晶格主要是指二阶非线性系数受到人工调制的微结构材料,其调制周期与光波的波长相比拟,通常为微米量级。铌酸锂(Lithium Niobate,LN)是最常用的光学超晶格材料之一,可以用来研究非线性光学现象,并恰好可以通过准位相匹配理论去补偿非线性过程中的位相失配,以此来产生或是调控非线性光学效应。本论文主要研究的是通过铁电畴反转制备光学超晶格,以及其在非线性光学方面的应用。具体包括以下几个部分:1.介绍介电体超晶格的概念与发展历程,从一维的周期结构到任意的二维结构,并着眼于其在非线性光学方面的应用,然后结合准位相匹配的理论,分析了光学超晶格在非线性频率转换中的作用;2.梳理了通过铁电畴反转制备光学超晶格的方法,包括生长条纹法、化学扩散法、电子束直写法、外加电场极化法等,重点研究了铌酸锂畴极化的过程与性质,主要包括五个过程:分别是反转畴的成核、反转畴的纵向生长、反转畴的横向扩张、反转畴的横向合并与自发的背向反转效应;3.详细介绍了我们制备图案极化铌酸锂薄膜的工艺流程,在外加电场极化法的基础上,我们不断改进工艺水平,优化工艺参数,能够在30-50 μm厚的铌酸锂晶体薄膜中,制备出任意的、二维的、均匀的、贯穿的、长期稳定存在铁电畴结构。通过选择性刻蚀之后,我们可以在光学显微镜下清晰地看到铌酸锂晶体薄膜的铁电畴结构;4.我们的制备方法具有很多优点,相比于传统的500 μm厚的铌酸锂晶体,这种极化方法易于操作,不需要苛刻的外部条件,本论文中所有的极化过程都是在常温常压下进行的。这种厚度的的LN晶体薄膜的铁电畴结构能够长期稳定的存在,不会消退;5.理论上分析了非共线的非线性倍频过程,主要包括非线性拉曼奈斯衍射及非线性切伦科夫衍射,分别是横向的位相匹配与纵向的位相匹配过程。然后我们利用制备的图案极化铌酸锂薄膜进行了实验验证,实验结果与理论计算十分吻合;6.最后,我们将全息技术引入非线性光学领域,基于制备的图案极化铌酸锂薄膜,可以对倍频光进行波前整形。在实验上,我们通过叉形光栅结构产生了倍频涡旋光,并设计了同心圆结构与分立点阵结构的铁电畴,产生了不同的非线性波前。
[Abstract]:Optical superlattices mainly refer to microstructured materials whose second-order nonlinear coefficients are manually modulated. The modulation period of optical superlattices is comparable to the wavelength of light waves and is usually of the order of micron magnitude.Lithium Niobate LN) is one of the most commonly used optical superlattice materials, which can be used to study nonlinear optical phenomena and compensate for phase mismatch in nonlinear process by quasi-phase matching theory.In this way, nonlinear optical effects are produced or regulated.In this thesis, we mainly study the fabrication of optical superlattices by ferroelectric domain inversion and their applications in nonlinear optics.It includes the following parts: 1.This paper introduces the concept and development of dielectric superlattice, from one-dimensional periodic structure to arbitrary two-dimensional structure, and focuses on its application in nonlinear optics, and then combines the theory of quasi-phase matching.The role of optical superlattices in nonlinear frequency conversion is analyzed.The methods of preparing optical superlattices by ferroelectric domain inversion, including growth stripe method, chemical diffusion method, electron beam direct-writing method, applied electric field polarization method and so on, were reviewed. The process and properties of domain polarization of lithium niobate were studied.There are five main processes: nucleation of reverse domain, longitudinal growth of reverse domain, transverse expansion of reverse domain, transverse combination of reverse domain and spontaneous reverse effect.The process of fabricating patterned lithium niobate thin films is introduced in detail. On the basis of the applied electric field polarization method, we continuously improve the process level and optimize the process parameters, which can be used in 30 ~ 50 渭 m thick lithium niobate crystal thin films.Arbitrary, two-dimensional, uniform, penetrating and stable ferroelectric domain structures have been prepared.After selective etching, the ferroelectric domain structure of lithium niobate thin films can be clearly observed under optical microscope.Compared with the traditional 500 渭 m thick lithium niobate crystal, this method is easy to operate and does not require harsh external conditions. All the polarization processes in this paper are carried out under normal temperature and atmospheric pressure.The ferroelectric domain structure of this thickness LN crystal thin film can exist steadily for a long time and will not fade away.The nonlinear frequency doubling process of noncollinear is analyzed theoretically, including nonlinear Raman diffraction and nonlinear Cherenkov diffraction, which are transverse phase matching and longitudinal phase matching, respectively.Then we use the patterned poled lithium niobate film to verify the experimental results, and the experimental results are in good agreement with the theoretical calculation.Finally, the holographic technique is introduced into the field of nonlinear optics. Based on the pattern-polarized lithium niobate thin films, the wavefront shaping of frequency-doubled light can be carried out.In the experiment, we have generated the frequency doubling vortex light through the forked grating structure, and designed the ferroelectric domains with concentric circle structure and discrete lattice structure, and produced different nonlinear wavefront.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O484
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本文编号：1705823