宽频带激光自由空间传输的调制特性研究

基于惠更斯-菲涅耳衍射积分公式,研究了宽带光束在菲涅耳衍射区的自由空间传输特性,得到宽带光束传输的调制深度与光束带宽Δλ及菲涅耳数F的变化关系。结果表明:一定的带宽对光束的均匀性有适当的改善;当光束的带宽Δλ<2λ0/F时,带宽越大,光束越均匀;当带宽满足条件Δλ=2λ0/F时,菲涅耳衍射完全消失;在一定的菲涅耳数范围内,宽带光束的调制深度随菲涅耳数振荡变化,振荡曲线的主极大值和次极大值分别出现在菲涅耳数为奇数和偶数处,而极小值则出现在菲涅耳数F=2k±1/3(k=1,2,3,…)处,在极小值处光束的均匀性最好。     

数值法研究光的圆孔衍射实验现象

在平行平面波近似的情况下,数值法求解菲涅耳-基尔霍夫衍射积分公式,得到平行平面光波通过圆孔衍射后的光强分布图.通过对纵向及横向光强分布图的数值分析,验证了轴上点光强由菲涅耳数决定,菲涅耳数大于1时为菲涅耳衍射区,菲涅耳数小于1时为夫琅禾费衍射区.在近场,光强分布为明暗相间的环形条纹;在远场,光束演化成束腰位置在圆孔处的高斯光束,仿真结果与理论和实验结果基本一致.本仿真结果将光衍射的抽象理论直观化、可视化.     

带电平面的反射与透射研究——菲涅耳公式的修正

根据一般条件下电磁场的边界条件,研究了两种介质分界面存在面电荷分布时的反射与透射,证明了这一条件下反射定律和折射定律仍然成立,推导得到存在面电荷分布时入射波平行分量和垂直分量的振幅反射系数和振幅透射系数,即修正的菲涅耳公式。由于不同界面的导电特性不同,两种介质界面的面电荷分布会影响界面的面电导率,修正后的菲涅耳公式与面电导率和自由空间阻抗有关。计算结果表明当面电荷密度或界面特性使面电导率发生较大变化时,振幅反射系数和振幅透射系数及反射率和透射率发生变化。     

菲涅尔公式的实验研究

菲涅耳公式是通过理论推导而得出的,在光学理论中占有重要地位,很多光学现象都可以用其解释,但这一公式却难于用实验直接验证。本文利用折射定律将菲涅耳公式形变处理,消除了不易测量的折射角,把不可测量的电矢量振幅转化为可测量的光强,并且选择在空气和水的分界面进行实验研究,使得菲涅尔公式的完整实验验证成为可能,实验曲线与mathematica软件数值模拟曲线完全吻合。     

平面透射光栅的菲涅耳衍射

从标量场的菲涅耳衍射理论出发,研究了球面波入射平面透射光栅的衍射场,导出菲涅耳衍射场的复振幅分布,并得到光栅菲涅耳衍射角的计算公式．结果表明,在理想情况下菲涅耳衍射的每一级衍射波都是一个球面波;在对菲涅耳衍射角进行新的定义后,衍射角的计算仍然可以采用夫琅禾费衍射的光栅方程．     

环状光束通过透镜的聚焦特性研究

给出了环状光束在柱坐标系下的一种描述模型,并利用广义衍射积分理论,推导出环状光束经过近轴ABCD光学系统的传输公式.在此基础上,通过数值模拟方法定量分析了环状光束的聚焦光强分布以及焦面处的桶中功率.研究结果表明,环状光束的聚焦特性与光束阶数以及系统菲涅耳数有关;环状光束在实际焦面和几何焦面上的桶中功率均随着遮拦比的增大而降低,而随着系统菲涅耳数的增大而增大.在实际工作中,通过合理地选取系统菲涅耳数和光束遮拦比可以有效地控制环状光束聚焦后的光束质量.     

高倍聚光光伏模组中三结太阳电池沿光轴方向光电性能与优化

目前,在高倍聚光光伏模组设计中,由于对菲涅耳透镜聚光后各波段的光强分布及其非均匀特性缺乏研究和认识,通常认为在菲涅耳透镜的聚光焦平面处多结太阳电池输出功率最大.本文通过光线跟踪模拟的方法,计算并分析菲涅耳透镜聚光下不同波段的光照能量分布和非均匀特性.同时,结合三结太阳电池电路网络模型,研究在高倍聚光光伏模组中,沿光轴方向不同位置处三结太阳电池的发电性能.结果表明:模组输出功率最高位置在焦平面沿光轴方向上下两侧的位置,优化后模组输出功率比常规设计提高20%以上.该模拟结果得到了实验结果的验证.     

显微数字全息中物光波前重建方法研究和比较

根据全息理论和线性系统理论,采用离轴无透镜傅里叶变换全息记录光路,对利用菲涅耳近似法、基于瑞利—索末菲衍射积分的卷积法以及角谱理论方法数值重建全息图进行了比较研究,并做了计算机模拟验证.结果表明：菲涅耳近似法和角谱方法重建像质比较好,且菲涅耳方法重建速度快;在记录距离极小的情况下,尽管记录距离不满足通常的菲涅耳近似条件,菲涅耳近似公式仍然成立;自由空间脉冲响应的快速傅里叶变换的性质与距离有关,由卷积方法得到的再现像只在某一特定距离下比较理想;对于极小物场、大孔径显微数字全息来说,菲涅耳近似重建方法是较为有效的方法.     

平面偏振光的布儒斯特入射

菲涅耳公式给出了两种透明介质界面处,平行入射面的光矢量(P矢量)和垂直入射面的光矢量(S矢量),在分界面上的振动状态[1].     

线宽误差对菲涅耳透镜衍射效率的影响

基于标量衍射理论,首先得出存在线宽误差情况下4阶菲涅耳透镜衍射效率的解析式;并以 4阶、8阶和16阶菲涅耳透镜为例,进行计算机模拟计算并系统分析线宽误差对菲涅耳透镜衍射效率的影响。通过实验测量16阶菲涅耳透镜的线宽误差,分析其对16阶菲涅耳透镜衍射效率的影响。模拟计算结果对多阶菲涅耳透镜的制作提供重要的理论指导。     

基于纳米覆膜光纤F-P传感器的折射率光谱特性

采用层层组装和化学共价交联的方法对光纤Fabry-Perot (F-P)干涉传感器的端面进行了纳米聚电介质覆膜修饰,并实验研究了覆膜后传感器的折射率响应光谱特性。选择聚二甲基二烯丙基氯化铵(PDDA)和聚苯乙烯磺酸钠(PSS)为纳米覆膜材料,随着覆膜层数的增加,光纤F-P传感器的反射谱对比度呈现由高到低,再到高的规律,且反射谱对比度具有良好的温度稳定性。选取覆膜层数为20双层的光纤F-P传感器对一系列浓度的蔗糖和无机溶液进行了折射率光谱响应测试,实验测得折射率检测拐点由1.457延伸至1.4623,对低折射率物质的折射率灵敏度为24.53 dB·RI-1,对高折射率物质的折射率灵敏度为3.60 dB·RI-1,且均具有良好的线性。研究结果为光纤F-P传感器对低折射率物质的功能化检测提供了新方法。     

UCN anomalous losses and the UCN capture cross section on material defects

Experimental data shows anomalously large ultra cold neutrons (UCN) reflection losses and that the process of UCN reflection is not completely coherent. UCN anomalous losses under reflection cannot be explained in the context of neutron optics calculations. UCN losses by means of incoherent scattering on material defects are considered and cross-section values calculated. The UCN capture cross section on material defects is enhanced by a factor of 10⁴ due to localization of UCN around defects. This phenomenon can explain anomalous losses of UCN.     

左手材料的反射特性与负折射率行为

利用平板波导法研究了不同入射角度下周期排列开口谐振环负磁导率材料、周期排列金属杆负介电常数材料以及左手材料微波反射特性，并利用劈尖法研究了左手材料的负折射特性.实验结果表明：负磁导率材料反射率曲线形成反射峰，其对应的反射峰频率与材料的谐振频率一致；负介电常数材料反射率接近0dB；左手材料出现单个反射较小的反射峰，其峰值反射率随入射角度的增大而变大，即反射能力增强，且反射峰与透射峰有相对频移.劈尖法测量还表明，左手材料在9800MHz频率附近出现负折射现象，其折射率n为-0.796. 关键词： 左手材料 反射 负折射率     

Coherent reflection of he atom beams from rough surfaces at grazing incidence

We report coherent reflection of thermal He atom beams from various microscopically rough surfaces at grazing incidence. For a sufficiently small normal component k(z) of the incident wave vector of the atom the reflection probability is found to be a function of k(z) only. This behavior is explained by quantum reflection at the attractive branch of the Casimir-van der Waals interaction potential. For larger values of k(z) the overall reflection probability decreases rapidly and is found to also depend on the parallel component k(x) of the wave vector. The material specific k(x) dependence for this classic reflection at the repulsive branch of the potential is discussed in terms of an averaging out of the surface roughness under grazing incidence conditions.     

Degree of polarization based on the three-component pBRDF model for metallic materials

An expression of degree of polarization(DOP) for metallic material is presented based on the three-component polarized bidirectional reflectance distribution function(p BRDF) model with considering specular reflection, directional diffuse reflection and ideal diffuse reflection. The three-component p BRDF model with a detailed reflection assumption is validated by comparing simulations with measurements. The DOP expression presented in this paper is related to surface roughness, which makes it more reasonable in physics. Test results for two metallic samples show that the DOP based on the three-component p BRDF model accords well with the measurement and the error of existing DOP expression is significantly reduced by introducing the diffuse reflection. It indicates that our DOP expression describes the polarized reflection properties of metallic surfaces more accurately.     

用于相位突变界面的广义的反射定律和折射定律

考虑到位于两物质界面上的Metasurface对光线传播行为的影响, 从费马原理和边界条件连续两种角度出发, 推导了可用于相位突变界面的广义反射与折射定律. 该定律在界面对光波的相位改变量为零的情况下, 回归为通常的反射定律和折射定律. 利用广义的折射定律和反射定律讨论了介质折射率、界面上的相位梯度等因素对光传播行为的影响, 发现利用广义的折射定律和反射定律很容易实现反常反射和反常折射行为, 并给出了出现反常反射和反常折射的条件, 以此为基础可以实现对光波的随意控制. 依据广义的折射定律和反射定律分析了一维相位掩模板对光场传播行为的影响. 关键词： 超材料 相位突变界面 反射定律 折射定律     

基于传输矩阵法讨论光疏介质表面的全反射

探究了光在光密介质与超薄光疏介质界面处的全反射,通过在光密介质中嵌入一光疏介质薄层,利用传输矩阵法,定量地分析了入射角度以及光疏介质的厚度对反射率的影响.数值模拟结果表明,当光疏介质的厚度小于约一个波长时,即使入射角大于全反射的临界角,反射率也不一定会达到1,也就是说,光学隧道效应将会出现.     

Reflection of compressional and Rayleigh waves on the edges of an elastic plate with quadratic nonlinearity

Previous ultrasonic studies have demonstrated that measurements of material nonlinearities can provide a means for detecting early signs of fatigue damage using both compressional (P) and Rayleigh (R) surface waves. However, these experimental studies have typically been limited to the direct wave arrival between the source and receiver in simple geometries where no reflection occurs. In particular, the degree of material nonlinearity is often quantified by the ratio of the cumulative amplitude of the first harmonic to that of the fundamental for the direct arrival only. Hence a practical question arises over the interpretation of ultrasonic measurements of material nonlinearities in the presence of reflected nonlinear waves. Thus, this article investigates the reflection problem of P or R waves at the edge of a homogeneous plate with quadratic nonlinearity using both a theoretical formulation, based on perturbation analysis, and direct numerical simulations using a Cellular Automata formulation. The numerical approach is first validated against an existing theoretical formulation for reflecting nonlinear P waves. It is then used to simulate the nonlinear reflection of R waves at a plate's edge for which no closed-form formulation is presently available.     

Control of the Rendition Wavelength Shifts of Color Lippmann Holograms Recordedin Single-layer panchromatic Silver-halide Emulsion

1 Introductionther hologratns can be used for artWork fabrication, product advertisement,museum item presentation, etc., and have wide applicationS in the world of businessand everyday life. To be able to record high-quality color reflection holograrns, it isnecessary to use extremely low scattering recording materials, for example, the use ofultra-high resolution silver-halide emulsions. Russian PFG-03C panchromatic silverhallde Plate is such a recording material, which has some excellent c…     

Control of the Rendition Wavelength Shifts of Color Lippmann Holograms Recorded in Single-layer panchromatic Silver-halide Emulsion

Russian PFG-03C panchromatic ultra-high resolution silver-halide emulsion is regarded as the most successful material for the fabrication of color reflection holograms. But the lack of established and reliable processing sequences prevents its practical applications in business and everyday life. Though much attention is drawn upon the processing of PFG-03C color reflection holograms, the color desaturation is still a problem. The article describes the new processing of color holograms recorded in PFG- 03C plates which is demonstrated experimentally to have the capacity of controlling the rendition wavelength shifts and improving the color desaturation effectively. The rendition spectra of Red-Green-Blue (R. G. B. ) single-line reflection holographic gratings, and the color reflection hologram as well, are given in this paper.