Irreversible effects of random modulation on coherence properties of partially polarized light

The effect of the multiplication of two vector electric fields by random Jones matrices on their coherence properties is investigated by analyzing their interference fringes. It is shown that these random modulations cannot increase the maximal visibility obtained when the polarization states of the two analyzed electric fields are optimized. This new result generalizes a standard property of perfectly polarized light to partially polarized light and is representative of the irreversible effects of random modulations.     

干涉条纹移动的偏振法

本文根据二个椭圆偏振光场进行的理论分析,着重讨论了两个相互正交的圆偏振光(左旋和右旋〕场和一个椭圆偏振光与线偏振光场的特点,以此为基础讨论了干涉条纹移动的偏振法。     

Interference of circularly polarized light: contrast and application in fabrication of three-dimensional periodic microstructures

The contrast of interference pattern formed by two circularly polarized waves and by a linearly polarized wave and a circularly polarized one is discussed. The results are compared with that by two linear beams. It shows that the use of circular light in holographic fabrication of three-dimensional periodic microstructures may remove the necessity of beam ratio and polarization optimization needed in the interference of three linear noncoplanar beams and improve the uniform contrast of resultant pattern simultaneously.     

双轴晶体会聚偏光干涉的理论与实验研究

晶体会聚偏光干涉图包含了晶体特性的许多信息,建立偏光干涉图的定量分析方法可以使这些信息得到充分利用。基于双轴晶体折射时满足的波矢关系,导出了两折射光波相位差的精确计算公式。分析了光波在各界面折射时偏振态的变化,提出了会聚偏光干涉合成振幅的计算方法。针对任意取向的双轴晶体,计算了完整的偏光干涉图,反映了相位分布决定等色线、振幅分布决定消光影的规律。用数字图像模似了干涉图,并讨论了干涉图的变化情况。对4块不同取向的KTP晶片进行实验,实验干涉图与理论干涉图的特征完全一致,两者仔细对比可判断现有KTP晶体色散方程的优劣。     

Mean-square coherent light

Mean-square coherent light is defined as light that is able to interfere with fringes of unit visibility when its electromagnetic field is multiplied by appropriate nonsingular deterministic Jones matrices. It includes light that satisfies the factorization condition at order one and partially polarized light that leads to interference fringes of unit visibility. A necessary and sufficient experimentally measurable condition to determine if two electromagnetic fields are mean-square coherent is established. Furthermore, different properties of partially polarized mean-square coherent light are discussed, such as its relation to the factorization condition and its evolution with propagation.     

两圆偏振光以及线偏振光和圆偏振光干涉图样的衬比度

考察了两束圆偏振光之间以及线偏振光与圆偏振光之间干涉所形成图样的衬比度,并与两束线偏振光之间干涉图样的衬比度进行了比较．指出在非共面多光束干涉中有可能利用圆偏振光以改善干涉图样的整体衬比度,并简要介绍了它在光子晶体制备中的应用．     

光的偏振性对Hanbury Brown-Twiss实验的影响

在理论和实验上研究了完全偏振光的不同偏振态和光的偏振度对Hanbury Brown-Twiss实验二阶关联函数g(2)的影响.实验中用线偏振光通过1/4波片获得椭圆偏振光,并通过旋转波片实现对完全偏振光偏振态的改变;用两柬振动方向相互垂直,传播方向相同且相位差随机的线偏振光合成部分偏振光,并通过调节一束光的光强实现对合成光偏振度的改变.结果表明:对于完全偏振光,其偏振态的改变对g(2)没有影响;对于不同偏振度P的光源,g(2)为P的二次函数.特殊地,自然光情况下P=0,g(2)的理论最大值为1.5;完全偏振光情况下P=1,g(2)的理论最大值为2.理论与实验符合得较好.     

基于正交调制的偏振光谱成像系统研究

为了同时获取目标的全偏振二维图像信息和其光谱信息,设计了一种基于正交调制的偏振光谱成像系统。该系统由光学接收模块、相位调制器、Wollaston棱镜、Savart偏光镜、检偏器以及成像模块组成。其可以将原始光信号分解成两束相互正交的偏振光,并且分别成像在CCD焦平面的上下两部分上,从而构成两幅偏振图像。两组图像的叠加可以将干涉条纹的数据相互抵消,从而获得目标的纯图像信息,两组图像的相减可以将目标灰度图像相互抵消,从而获得目标的纯干涉条纹。通过理论分析与计算得到了光强分布函数和光谱变化形式。实验在稳定的光源环境中采用高对比度目标与背景板,完成了全偏振图像的实时采集。经相位校正和切趾处理改善了干涉图像的畸变,又通过去低频滤波和阈值滤波抑制了图像中背景噪声的影响,从而实现了对目标图像的提取及偏振光谱的复原。该系统具有稳定性高、光谱分辨率可调、信噪比高、可识别能力强等特点,对在复杂背景中提取目标图像、光谱及偏振态信息具有重要意义。     

Vector Approach to Calculating Space-Charge Fields in Crystals withntrast Light Interference Pattern

A new method for calculating space-charge fields in photorefractive crystals with shallow-lying traps illuminated by a light interference pattern of arbitrary contrast and shape is suggested. A space-charge field in a BSO:Cd crystal with shallow-lying traps illuminated by a sine light interference pattern with the high contrast m = 0.99 is calculated.     

Experimental demonstration of three mutually orthogonal polarization states of entangled photons

Linearly polarized classical light can be expressed in a vertical and a horizontal component. Geometrically rotating vertically polarized light by 90 degrees will convert it to the orthogonal horizontal polarization. We have experimentally generated a two-photon state of light which evolves into an orthogonal state upon geometrical rotation by 60 degrees. Rotating this state by an additional 60 degrees will yield a state which is mutually orthogonal to the first two states. Generalizing this procedure, one can generate N+1 mutually orthogonal N-photon states that cyclicly evolve from one to another upon a geometric rotation by 180/(N+1) degrees.     

Effects of coherence on the degree of polarization in a young interference pattern

Recent predictions concerning the relationship between the degree of polarization at a typical point of a Young interference pattern and the degree of coherence of the electromagnetic field at the pinholes are tested by a simple experiment. In particular, it is shown that light that is completely unpolarized at the pinholes can become partially polarized across the fringe pattern.     

Model description of the degree of polarization of nonstationary light waves

A theoretical approach is developed that provides the possibility of representing partially polarized radiation in the form of a sum of mutually orthogonal polarized and incoherent components and in the form of a model device with a time-dependent circular birefringence. This approach allows one to apply the vectormatrix Jones method in calculations. The possibility of theoretically determining the degree of polarization of the light passed through a corresponding device placed in an external magnetic field is shown as an illustration.     

Interference effect in the photoproduction of electron-positron pairs on a nucleus in the field of two light waves

In the general relativistic case, the nonresonance photoproduction of electron-positron pairs on a nucleus in the field of two circularly polarized light waves propagating in one direction is theoretically investigated. It is shown that there are two essentially different kinematical regions: the noninterference region, where the Bunkin-Fedorov quantum parameters play the role of multiphoton parameters, and the interference region, where interference effects are important and where quantum interference parameters are treated as multiphoton parameters. The interference effect is found in the photoproduction of an electron-positron pair on a nucleus in the field of two light waves. This effect occurs in the interference region and is due to the production of an electron-positron pair in the plane spanned by the light wave vector and the incident-photon momentum and to stimulated correlated emission and absorption of photons of the two waves. The cross sections for pair photoproduction on a nucleus in the above kinematical regions are determined for moderately strong fields. It is shown that, in the interference region, the partial cross sections for the case where there is a correlated emission (absorption) of the same number of photons of the two waves can significantly exceed the corresponding cross sections in any other geometry.     

Interference of four umbrellalike beams by a diffractive beam splitter for fabrication of two-dimensional square and trigonal lattices

A simple optical interference method for fabricating two-dimensional square and trigonal lattices is demonstrated. A general formula for the interference contrast formed by two arbitrary polarized elliptical waves is deduced, the relation between wave vectors of incident light and the resultant pattern is analyzed, and polarization optimization of all beams to ensure uniform contrast is given.     

Full-range, complex spatial light modulator for real-time holography

We demonstrate a full-range complex and transmissive spatial light modulator (SLM) for simultaneous and independent amplitude and phase modulation of an input wave field. Arbitrary scalar complex optical fields are generated by stacking a pixelated liquid crystal display operating in phase-only (2π) modulation with passive polarization-sensitive components. The principle is based on optical combining the light fields of two neighboring phase-only modulating pixels, which were made orthogonally polarized by a structured half-wave plate, then passing through a birefringent plate to laterally shift one of the beams collinear to the other, and finally bringing to interference by a linear polarizer. Complex modulation by the proposed SLM is experimentally verified in monochrome green operation.     

Extracting the phase distribution of the electron wave packet ionized by an elliptically polarized laser pulse

We use an interferometic scheme to extract the phase distribution of the electron wave packet from above-threshold ionization in elliptically polarized laser fields. In this scheme, an electron wave packet released from a circularly polarized laser pulse acts as a reference wave and interferes with the electron wave packet ionized by a time-delayed counter-rotating elliptically polarized laser field. The generated vortex-shaped interference pattern in the photoelectron momentum distribution enables us to extract the phase distribution of the electron wave packet in the elliptically polarized laser pulse with high precision. By artificially screening the ionic potential at different ranges when solving the time-dependent Schördinger equation, we find that the angle-dependent phase distribution of the electron wave packet in the elliptically polarized laser field shows an obvious angular shift as compared to the strong-field approximation, whose value is the same as the attoclock shift. We also show that the amplitude of the angle-dependent phase distribution is sensitive to the ellipticity of the laser pulse, providing an alternative way to precisely calibrate the laser ellipticity in the attoclock measurement.     

三维电子散斑干涉技术及其应用研究

通过大错位剪切镜和一作为参考物的压电陶瓷相移器将三个电子散斑干涉系统组成一新的三维电子散斑干涉系统。利用该系统，结合相移技术和图像处理技术，可得到独立的位移场(u,v和w场)。该技术的特点是用三个激光器作为光源，一个压电陶瓷相移器产生参考光并实现相移，CCD摄像机前放置大错位剪切镜以使物光和参考光产生干涉。将该技术应用到柴油发动机零部件测量上，得到了主轴承孔周的三维位移场。     

Focusing property of a double-ring-shaped radially polarized beam

The intensity distributions of a tightly focused radially polarized beam that has a double-ring-shaped transverse mode pattern were calculated based on vector diffraction theory. The distribution of the longitudinal component near the focus varied drastically with the degree of truncation of the incident beam by a pupil. When the ratio of the pupil radius to the beam radius was approximately 1.3, the longitudinal component disappeared at the focal point, owing to destructive interference. This dark area surrounded by an intense light field was of the order of the wavelength, with excellent intensity symmetry.     

调制偏振光及空间正交方位信息传递系统物理模型

受到调制的偏振光可作为方位信息的载体在空间传递，从而实现方位角度信息的传递和精密测量，这是偏振光的一个新的应用领域，在航空航天、地质测量、生物医药、军事等领域具有广泛的应用前景．文章首先介绍了调制偏振光的物理意义和空间正交方位信息传递系统的应用领域，然后介绍了利用调制偏振光进行空间正交方位信息传递系统的物理模型，并分析了一个具体实现方案．     

一种液晶透镜盒间隙的测试方法

针对当前液晶透镜盒间隙测试存在的难题, 文中提出采用线偏振干涉法测试方法, 采用光强均匀分布的单色光入射, 检偏器的偏光轴方向与起偏器的偏光轴垂直或者平行, 液晶透镜的液晶取向层的摩擦方向与起偏器偏振轴夹角为45°, 此时干涉条纹亮暗差别最明显. 利用液晶透镜中心保持预倾角不变的透过率以及其他位置透过率最大值来计算液晶透镜的盒间隙, 该方法简单、可靠, 因采用光学手段测试, 其精确度相对较高. 关键词： 液晶透镜 盒间隙 线偏振光干涉 透过率