LiNbO_3:Fe的光致光衍射

本文研究了单光束辐照厂LiNbO_3:Fe的衍射光锥。它可以考虑为入射光束与其晶体后表面反射束及由晶体缺陷所致的散射光束的简并四波混频。光锥的锥角由其位相匹配条件△k=0确定。它可用Ewald球的作图法求解。同时也讨论了一种由时间分辨简并四波混频所产生的衍射光锥。实验结果与理论一致。     

LiNbO3:Fe的光致光衍射

本文研究了单光束辐照厂LiNbO₃:Fe的衍射光锥。它可以考虑为入射光束与其晶体后表面反射束及由晶体缺陷所致的散射光束的简并四波混频。光锥的锥角由其位相匹配条件△k=0确定。它可用Ewald球的作图法求解。同时也讨论了一种由时间分辨简并四波混频所产生的衍射光锥。实验结果与理论一致。 关键词：     

基于大数值孔径环形光锥照明的超分辨光学 显微成像方法研究

提出和发展了一种基于大数值孔径环形光锥照明的远场超分辨光学显微成像新方法, 采用将发光二极管(LED)面光源、窄带滤光和环形光锥照明相结合的特种照明方式, 实现超分辨显微成像. 建立了大数值孔径环形光锥照明成像的物理模型, 根据标量衍射理论, 在不同环形光锥照明时, 推导出光学显微系统像面衍射斑光强分布的理论计算公式; 通过Matlab求解和绘图, 得到衍射斑光强的分布图样, 从理论上证明这一成像方法可以有效提高光学显微镜的分辨率; 建立了相应的显微成像系统, 通过实验验证了该方法可有效改善显微镜的成像质量, 显著提高分辨率; 在中心波长450 nm、环形光锥数值孔径1.125—1.25时, 实验获得的分辨率至少优于150 nm, 与理论研究结果相符合, 从而证明了这一方法的可行性.     

碱性品红光致聚合物薄膜的光致光衍射

本文研究了全息存储实验中以波长532 nm的半导体激光器作为记录和读出光源,碱性品红作为光敏剂的丙烯酰胺基光致聚合物薄膜的光致光衍射现 象.它可以考虑为透过全息干涉条纹的原始入射光和反射光,与来自光聚物中未曝光的不均匀表面和内部的散射光四波混频的结果.根据简并四波混频理论中的位相匹配条件对双光束全息写入时产生的衍射光锥,以及单光束辐照复现时产生的衍射光锥现象分别做出了理论解释;并且利用全息散射理论结合三角学知识对入射光的入射角与衍射光锥的锥角的依赖关系进行了深入讨论. 关键词： 全息 光致聚合物 衍射光锥 碱性品红     

基于PVA／AA光致聚合物的衍射光锥产生机理及其抑制

研究了以He—Ne激光器作为记录光源,以He-Ne、Nd：YAG和He-Cd激光器作为读出光源的亚甲基蓝敏化的PVA／AA体系光致聚合物的全息衍射光锥现象。衍射光锥现象的产生是由于入射光透过全息记录材料内部的不均匀结构或缺陷所产生的噪音光栅所致。运用Ewald球对此现象产生的机理进行了解释,利用全息光散射理论结合三角学...     

掺杂KNSBN晶体各向异性自衍射的耦合波分析

在晶体光轴垂直于入射面的各向异性实验组态下,对掺杂KNSBN晶体的各向异性自衍射过程进行了理论分析和实验观测,给出了包含空间电荷场前两阶分量作用的各向异性自衍射的耦合波方程及其数值解。理论分析和实验结果都表明各向异性自衍射光来自于两束入射光的共同作用。     

圆柱体的空间圆锥光反射、折射与衍射

用准直或会聚激光束倾斜照射圆柱体时,其反射光、透射光(柱体透明时)、衍射光(柱体较细时)的叠加将形成以光束入射点为顶点的空间圆锥形光面(空间光锥),并且在垂直于柱体轴线方向的观察平面上投影成一圆形光环.空间光锥的形成与所选圆柱体材料及其粗细无关,只要其表面具有一定反射能力即可.空间光锥的锥角等于入射光束主光轴与圆柱体轴线夹角的2倍,与圆柱体和照射光束的直径大小及光波长无关.给出了对光纤及不同直径大小的玻璃和金属圆柱体的实验观察结果,并利用矢量图解法对其进行了详细地理论分析.进而得出,通常所谓单丝衍射图样,实际上是细丝的衍射和其表面的反射光场的叠加图样,对于透明细丝,还包括其透射光场的贡献.圆柱体的这种空间圆锥光反射和衍射原理有可能用于光束定位、成形、表面检测以及三维面形测量等 关键词： 圆柱体 空间光锥 投影光环     

c向切割LiNbO3:Fe晶体薄片中的四波混频各向异性光散射

报道了在ｃ向切割ＬｉＮｂＯ₃：Ｆｅ晶体薄片的前向光散射中观察到的一种新的类似鸭蛋形的各向异性衍射光环图样，并且提出了由入射光、强的背向散射光而引起的四波混频各向异性光散射机制，圆满地解释了有关实验结果。 关键词：     

激光束在LiNbO_3:Fe晶体中的异常衍射现象(Ⅰ) e光入e光出的衍射

根据的相位光栅各向异性衍射理论,应用顾世杰、李荫远发展的方法,对于激光束在厚的LiNbO_3:Fe晶体(厚度≈1cm)中的异常衍射现象作了计算。如果晶体中被照射后有无规的电荷富集分布,则Fourier分解后可得到无穷个相位光栅,衍射图形决定于光栅的衍射效率。计算结果表明,对e光入e光出的衍射图形,可以解释中央光斑(由透镜效应所决定)两边的光瓣。结果与实验基本符合。     

记录结构对体光栅各向异性衍射选择特性研究

以静态体光栅各向异性衍射理论分析模型为基础，将与体光栅厚度有关的记录光强调制度引入到各向异性耦合波方程中.利用耦合波理论分析了光折变晶体中体光栅的各向异性衍射性能，研究了在不同初始记录光强比的条件下，记录光入射角的改变对光折变体光栅各向异性布喇格衍射性能的影响.结果表明：记录光入射角和记录光初始光强比均对体光栅的各向异性衍射具有选择性；与此相比，记录光入射角和记录光初始光强比对于体光栅各向同性衍射不具备选择性.     

Effect of recording conditions on the anisotropic diffraction of volume holographic gratings

The anisotropic Bragg diffraction of the volume holographic gratings in photorefractive crystals are investigated based on the model of anisotropic coupled-wave theory. The effect of the initial intensity ratio and the recording angles of the two recording waves on the anisotropic Bragg diffraction properties is discussed. It is shown that both the ratio of the initial intensity and the incident angles of the recording waves are selective action for the anisotropic Bragg diffraction efficiency of the volume holographic gratings, while these two recording conditions are not selective action for the isotropic Bragg diffraction. Furthermore, the Bragg phase matching condition of anisotropic diffraction is analyzed when the recording angles change.     

Ultrasonic diffraction of Bessel light beams in uniaxial gyrotropic crystals

Specific features of the acousto-optic diffraction of Bessel light beams propagating in the vicinity of the optical axis of a uniaxial gyrotropic crystal have been investigated. The dependences of the diffraction efficiency on the acousto-optic interaction length, ultrasound power, and polarization state of the incident Bessel light beam have been analyzed using the coupled-wave equations and the overlap-integral method. It is shown that polarization-independent diffraction of Bessel light beams is observed in paratellurite crystals, when the Bragg diffraction efficiency is independent of the polarization state of the incident beam. The physical reason for this diffraction has been established (both theoretically and experimentally) to be simultaneous implementation of two processes of anisotropic scattering, at which the Bragg synchronism conditions are satisfied for orthogonal polarized Bessel beams with elliptical polarization.     

Double Bragg and Bragg/normal diffraction of two laser beams by ultrasound

An accurate theory is developed describing the diffraction of two light beams incident at various Bragg angles on an ultrasonic beam, taking into account the phase-difference between the two light waves. The general results are outside the range of the Raman-Nath approximation and a comparison is made with an alternative configuration in which one of the light waves is normally incident.     

Anisotropic and valley-resolved beam-splitter based on a tilted Dirac system

We investigate theoretically valley-resolved lateral shift of electrons traversing an n–p–n junction bulit on a typical tilted Dirac system (8-Pmmn borophene). A gauge-invariant formula on Goos–Hänchen (GH) shift of transmitted beams is derived, which holds for any anisotropic isoenergy surface. The tilt term brings valley dependence of relative position between the isoenergy surface in n region and that in the p region. Consequently, valley double refraction can occur at the n–p interface. The exiting positions of two valley-polarized beams depend on the incident angle and energy of incident beam and barrier parameters. Their spatial distance D can be enhanced to be ten to a hundred times larger than the barrier width. Due to tilting-induced high anisotropy of the isoenergy surface, D depends strongly on the barrier orientation. It is always zero when the junction is along the tilt direction of Dirac cones. Thus GH effect of transmitted beams in tilted Dirac systems can be utilized to design anisotropic and valley-resolved beam-splitter.     

The spectral combination characteristic of grating and the bi-grating diffraction imaging effect

This paper reports on a new property of grating, namely spectral combination, and on bi-grating diffraction imaging that is based on spectral combination. The spectral combination characteristic of a grating is the capability of combining multiple light beams of different wavelengths incident from specific angles into a single beam. The bi-grating diffraction imaging is the formation of the image of an object with two gratings: the first grating disperses the multi-color light beams from the object and the second combines the dispersed light beams to form the image. We gave the conditions necessary for obtaining the spectral combination. We also presented the equations that relate the two gratings’ spatial frequencies, diffraction orders and positions necessary for obtaining the bi-grating diffraction imaging.     

Propagation properties of beams generated by Gaussian mirror resonator in uniaxial crystals

Based on the paraxial vectorial theory of beams propagating in uniaxially anisotropic media, we have derived the analytical propagation equations of beams generated by Gaussian mirror resonator (GMR) in uniaxial crystals, and given the typical numerical example to illustrate our analytical results. Due to the anisotropy crystals, the ordinary and extraordinary beams originated by incident beams generated by GMR propagate with different diffraction lengths, thus the linear polarization state and axial symmetry of the incident beams generated by GMR do not remain during propagating in crystals.