The use of defocussed position of a Ronchi grating for evaluating the refractive index of lens

This report describes a Ronchi-grating shearing interferometric collimation method for determining the refractive index of a lens. A new formula has been deduced for the refractive index of the lens, which is independent of lens parameters. This newly developed device has two lenses. One of them collimates the light from a point source while the other acts as a decollimator. The point source acting as a test target is situated in the front focal plane of the collimator. The test lens is placed inside a glass cell in the back focal plane of the collimator. The Ronchi grating is exactly placed in the back focal plane of the decollimator, and a fringe-free space is observed in the common region. When the test lens is immersed in a liquid cell, it disturbs the focal point and hence interference fringes are observed. The combined system consisting of the test lens and the decollimator is moved to bring the focal point on the Ronchi grating. Thus, the difference between the two settings gives the amount of defocusing.     

X‐ray focusing by the system of refractive lens(es) placed inside asymmetric channel‐cut crystals

An X‐ray one‐dimensionally focusing system, a refracting–diffracting lens (RDL), composed of Bragg double‐asymmetric‐reflecting two‐crystal plane parallel plates and a double‐concave cylindrical parabolic lens placed in the gap between the plates is described. It is shown that the focal length of the RDL is equal to the focal distance of the separate lens multiplied by the square of the asymmetry factor. One can obtain RDLs with different focal lengths for certain applications. Using the point‐source function of dynamic diffraction, as well as the Green function in a vacuum with parabolic approximation, an expression for the double‐diffracted beam amplitude for an arbitrary incident wave is presented. Focusing of the plane incident wave and imaging of a point source are studied. The cases of non‐absorptive and absorptive lenses are discussed. The intensity distribution in the focusing plane and on the focusing line, and its dependence on wavelength, deviation from the Bragg angle and magnification is studied. Geometrical optical considerations are also given. RDLs can be applied to focus radiation from both laboratory and synchrotron X‐ray sources, for X‐ray imaging of objects, and for obtaining high‐intensity beams. RDLs can also be applied in X‐ray astronomy.     

Aberrations of self-imaged patterns with two-dimensional periodicity

We develop a geometrical theory of aberration in the self-imaged patterns with two-dimensional periodicity. The patterns are considered to be a crossed-line grating or a periodic array of finite apertures. We first derive the raytracing equations for determining the optical path of a self-imaging ray. We then find the third- and fifth-order contributions to the wavefront aberration which arise from the difference between the optical paths of a self-imaging ray and of an actual ray. We also derive the expression of the ray aberration from the wavefront aberration. The ray aberration is classified into five distinct types by analogy with the cases in a refracting lens system. We show that the overall ray aberration is entirely undercorrected and the aberrated image patch is decentered from an ideal image point in the direction parallel to the direction tangent vector of a chief ray. The image evaluation technique discussed here will be useful in various applications related to self-image formation of two-dimensionally periodic patterns.     

利用保角变换实现环形光栅的Talbot效应

Talbot效应是一种近场自成像效应,通常只有周期光栅可以产生Talbot效应,而环形光栅无法产生.本文通过引入保角变换,发现可以在环形光栅外部设计适当的折射率渐变层介质,使得其中也能够产生严格的Talbot效应,并计算了对应的自成像半径表达式.本文利用FDTD软件分别将一个环形光栅放置在真空中以及人工设计的折射率渐变层中进行了模拟,并对二者的结果进行了比较分析,发现这种折射率渐变层介质确实对点光源入射的环形光栅的自成像情况有着很好的改善.希望这一工作能够推广Talbot效应的应用范围.     

基于二次成像的像面干涉高光谱成像方法

像面干涉高光谱成像技术主要应用于遥感成像领域,为了实现不同距离目标的光谱成像探测,提出了一种基于二次成像的像面干涉高光谱成像方法。通过在无限远成像系统中加入前端成像物镜、中继准直物镜和横向剪切分束器,构建一个二次成像的干涉系统。通过采用分离式的前端成像物镜方案,选用变焦镜头或不同焦距的定焦镜头,有效地兼顾远、近距离目标的成像光谱探测。对该方法的成像系统、光谱分辨率和推扫方式等方面进行了分析,进一步搭建了实验装置,对室内近场目标和室外远场目标进行了成像实验,并对生物组织进行了显微光谱干涉成像实验。实验结果表明,该成像方法能够有效用于不同距离目标的高光谱成像探测。     

空-频域中自成像分析和解释

基于魏格纳变换和魏格纳分布函数,分析讨论一维物体在空域-频域空间的自成像及其形成过程。从成像过程中各衍射频谱分量的光程差出发,给出Talbot效应和Montgomery效应的统一解释。对于周期物的Talbot效应,得到了用杨氏双缝干涉解释自成像现象的理论依据。周期物的自成像是物平面上间距为2倍周期,光程差为波长的整数平方倍的各衍射频谱分量同相相干迭加的结果。Montgomery效应是物平面上间距为抛物线关系,光程差为波长整数倍的各衍射频谱分量同相相干迭加的结果。     

A simple method for testing laser beam collimation

A simple and improved method is proposed for testing laser beam collimation by a new type of grating, comprising concentric equilateral triangles and the mirror images of these triangles. Although this type of grating possesses one-dimensional periodicity in a particular direction and inherent defects in periodicity, the moiréfringe pattern formed by placing an exact replica of such a grating at its self-imaging plane shows that the self-imaging phenomenon takes care of the defects in the periodic objects.     

Geometrical aberrations of self-imaged line gratings

We analyze the properties of a self-imaging system from the point of view of aberration theory. We examine analytically and numerically the geometrical aberrations that are observed in the self-image of a parallel-line grating. We first derive the raytracing equations for determining the optical path of a self-imaging ray with the order of diffraction l. We then obtain the third- and fifth-order contributions to ray aberrations which arise from the difference between the optical paths of a self-imaging ray and of an actual ray. We show that the overall ray aberrations are entirely undercorrected. The ray aberrations approach zero as the ratio of the grating constant to the wavelength of light becomes large enough. In a case of unit magnification, no curvatures are observed in the self-imaged lines. If the magnification is bigger than unity, the light rays passing through the point in a positive or negative domain of the aperture variable contribute to the formation of the curved images. The image evaluation technique discussed here can be useful in the various applications related to the self-image formation of a parallel-line grating and it can also provide insight into the self-imaging of other periodic objects.     

Negative refractive behavior of a two-dimensional negative-index photonic crystals using a wave vector diagram method

We have theoretically studied the negative refractive behavior and the focusing effect in a two-dimensional square-lattice photonic crystal made of air rods in a dielectric background. Detailed explanations are given for the effect of the negative refraction, and the imaging of the plano-concave lens is shown by the use of a wave vector diagram formalism. The typical negative refractive behavior is demonstrated by considering the Bloch mode with the wave vector inside the first Brillouin zone, because only those wave vectors inside the first Brillouin zone of multiple Brillouin zones have a definite meaning. The single propagating beam is analyzed by the use of the wave vector diagram formalism following the folding of the wave vectors. Good-quality focusing of a plane wave can be realized by using a photonic crystal plano-concave lens, while a plane wave is formed by a point source placed at the focal point. Our results are in good agreement with the experimental ones shown for a negative-index plano-concave lens by Vodo et al. [Appl. Phys. Lett. 86 (2005) 201108]. Finally, we also have shown the focusing behavior of a plane wave and a Gaussian pulse by a plano-concave lens structure with high-index modulation instead of air in the concave region.     

基于LCTF的便携式多光谱成像仪

选用商品化照相机镜头、液晶可调谐滤光片（Liquid Crystal Tunable Filter,LCTF）和单色面阵CCD相机,将LCTF置于由镜头和CCD相机组成的照相光路中构成便携式多光谱成像仪,该多光谱成像仪能够在被动和主动光源下进行多光谱图像数据采集,工作波长范围是400-720nm,光谱分辨率为10nm,建立了多光谱成像仪系统多光谱图像采集数值模型,分析了误差源,为系统定标提供了理论依据。最后在自然光照条件下进行了盆景植物的多光谱图像采集试验,重建出多光谱数据立方体,绘制了典型目标点的光谱曲线。     

Influence of distances between the lens and the target on the characteristic of laser induced lead plasma

The influence of distances between the lens and a pure lead target on the breakdown spectroscopy of plasmas induced by a Nd:YAG laser ablation was studied at atmospheric pressure. The electron density, the electron temperature and the self-absorption were analysed when the distances were less than the focal length (6.5 cm). The maximal electron density presented at the point 5.8 cm. Moreover, the self-absorption can be observed in all of the wave ranges when the distances are more than the focal length. This phenomenon can be understood by the air breakdown.     

Defect enhancement in periodic masks using 1/2-Talbot effect

In this paper, we present a simple system for defect enhancement in periodic masks, enabling in this way their rapid localization. The system uses the fact that periodic structures under coherent illumination generate replicas of itself displaced half period at certain distances (1/2-Talbot’s length). Projecting back this displaced self-image onto the mask creates a suppression of the periodic structure. If the mask presents defects, the cancellation of the periodic structure allows their detection since the self-imaging phenomenon occurs only for the periodic structure. The technique may be applied to transmission masks like semiconductor wafers, photomasks for integrated circuits or LCD panels.     

调焦方式对测绘相机主点位置的影响

考虑测绘相机调焦会影响相机的主点位置,从而改变相机的内方位元素,降低立体测绘精度,故本文分析了空间相机常用的3种调焦方式（镜组调焦、平面反射镜调焦、焦面调焦）对测绘相机主点位置的影响。简要介绍3种调焦方式的工作原理,研究了理想情况下3种调焦方式对主点位置的影响。在考虑系统装凋误差的情况下,建立了主点位置变化量与调焦量之间的数学模型,通过实例计算得出焦面调焦易满足测绘相机主点定位精度〈0．2pixel,是最适合的调焦方式。最后,以某一型号相机调焦机构为实验对象,对平面反射镜方式对主点的位置变化进行了实验量测,结果证明了提出的主点位置变化量理论计算公式的准确性和分析得到的不同调焦方式对主点位置影响的正确性,该公式可以用于指导测绘相机调焦方式的选择,以满足高精度测绘的需要。     

Multi-band imaging and focusing of photonic crystal flat lens with scatterer-size gradient

In this Letter, a photonic crystal(PC) flat lens with a scatterer-size gradient is proposed, which simultaneously achieves imaging of the point source and sub-wavelength focusing of the plane wave in the first, second, and fifth bands. The imaging of the point source breaks through the diffraction limit in the second and fifth bands. The PC flat lens with the scatterer-size gradient is expected to be used in a new multifunctional optical imaging and focusing device, which improves the application potential of a PC flat lens.     

超短脉冲经过小数值口径透镜的聚焦特性

 从亥姆霍兹方程出发，考虑透镜的色差和球差，得到了超短脉冲经过小数值口径透镜后光场的解析表达式；利用数值模拟得到了旁轴焦平面和边缘焦平面上光场强度的时空分布，以及聚焦区域内轴上点的强度分布图，并分析了色差和球差的大小对它们的影响。由于通过透镜中心和边缘之间的大部分脉冲产生了干涉相消，因此在旁轴焦平面与边缘焦平面上都出现前、后两个峰值相差很大的脉冲，并且随着球差的增大，两峰值差更大了；聚焦区域内轴上点的强度分布基本是对称的，强度最大点不是出现在旁轴和边缘焦平面上，而是在它们之间的某个位置，并且随着球差的增加，该位置将向聚焦区域的边缘靠近。     

Determination of the focusing power of flat lenses using the radiovisor

Focusing of electromagnetic radiation of a point source with a wavelength of 3 cm by flat negative-refraction lenses formed by a hexagonal structure of metal cylindrical rods was studied. The spatial distribution of microwave field of H polarization in the lens focal plane was recorded by a radiovisor screen which converts it into a visible image. The full width at half maximum of the focal spot distribution at optimum focusing did not exceed half the emission wavelength.     

CCD辅助测量凸透镜焦距的一种新方法

本文针对凸透镜主点及物像平面难以精确定位的问题,提出了一种以理想光学系统的物像关系为理论基础,基于高斯公式,用CCD摄像机辅助的精确测量凸透镜焦距新方法,这种方法也可以在焦距未知的情况下,求共轭距。     

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.     

Practical issues for two-light-sources model of phosphor-based white light-emitting diode

We report an intuitive approach to simulating the performance of the phosphor-based light emitting diode (LED) by using the two-light-sources model for an optimized LED lens. The optimized secondary lens shape is achieved by approaching a uniform energy distribution on the detecting plane. Both the spectrum and spatial apodization of the LED structure are discussed, and the results indicate that the two-light-sources model can solve the misleading design on the phosphor-based LED due to imperfect color mixing of light source, that one can satisfy the highly uniformity requirement for specific applications, such as display backlight or optogenetic.     

空间周期相干光照明下的自成像现象及Lau效应

借助模糊函数理论分析了空间周期相干光照明产生的自成像现象及Ｌａｕ效应。理论分析结果表明：当照明光源满足一定条件时，会出现自成像现象及Ｌａｕ效应。根据分析结果讨论了这些现象的可能应用。