双折射双频激光器输出光偏振特性的实验研究

报道了双折射双频激光器输出光偏振特性的实验研究，实验发现双折射双频激光器两端输出的线偏振光的偏振方向并不一致，而相互有一定的旋转角度，实验也再次证明了激光器输出的是正交线偏振光，而不是晶体本征模的椭圆化了的偏振光。     

Effect of polarization on focal depth in high numerical apertures optical systems

The generalized cylindrical vector beam is just a linear combination of radial and azimuthal polarization. For radially polarized light in the focal plane, there are two electric field components, the radial component and z-component whose magnitude increase with the increase of numerical aperture. By contrast, for azimuthally polarized light in the focal plane, there is only one electrical field component in the azimuthal polarization, it is easy to understand the difference between the two polarization effects. In this paper, we demonstrate how this phenomenon can be harnessed to make a properly selected polarization component to achieve high focal depth in high numerical aperture systems. Numerical simulations show that the evolution of the focal shape is very considerable by changing polarization rotation angle of the generalized cylindrical vector beam. And some interesting focal spots and focal split may occur. And if the ratio of radial and azimuthal polarization is set properly by changing the polarization rotation angle, a largest focal depth is achieved. The tunable range of the focal depth is very considerable. The ratio of radial and azimuthal polarization is different in different NA optical system for obtaining the largest focal depth. We will denote a technique of polarization-assisted high focal depth in high numerical aperture systems.     

Analytical approach of developing wavelength encoded AND, NAND and X-OR logic operations and implementation of the theory using semiconductor optical amplifiers

Frequency encoding technique is a very promising and faithful technology for very fast long-haul optical communication and super fast computation. Implementation of different logic gates based on the principle of frequency conversion is the key mechanism of frequency encoded data processing and networking. It is established that semiconductor optical amplifiers (SOA) have been used successfully for the purpose of frequency conversion. One of the important techniques of frequency conversion is the conjugate beam generation by four wave mixing (FWM) in SOA and ultimately conversion of it into desired frequency by means of reflecting semiconductor optical amplifier (RSOA). However the efficiency of conjugate beam generation is restricted by polarization dependent gain saturation of SOA. This dependency can be successfully removed using polarization diversity scheme. Another technique of the frequency conversion is based on nonlinear rotation of the state of polarization of the linearly polarized probe beam. An important advantage of using polarization rotation in SOA is that a small change in rotation of the state of polarization will lead to a large difference in output power. Here in our present communication we propose a method of developing wavelength encoded AND, NAND and X-OR logic operations exploiting the above mentioned functions of SOA. For this purpose we have developed an analytical treatment based on which above mentioned three logic gates are conducted. The satisfactory simulation result proves also the validity of the developed theory.     

Laser pumping and magneto-optical rotation of the light polarization plane in a cell with an antirelaxation coating of the walls: II. Calculation for atoms with the Λ scheme of sublevels

The general solution of the Boltzmann kinetic equations obtained previously by the author for the atomic density matrix in a long cylindrical cell with an antirelaxation coating of the walls under conditions of laser pumping in a magnetic field is used for the calculation of the magneto-optical rotation of the light polarization plane. It is shown that, in accordance with experimental data, the dependence of the rotation angle of the polarization plane of the pumping light on a magnetic field ranging from ?1 to 1 Oe represents a sum of two antisymmetric curves: a narrow curve with a spacing between extrema of about 2 μOe and a broad curve with a spacing of about 0.03 Oe. It is found that the characteristics (the width and the amplitude) of these two curves depend quite differently on the parameters of the problem—the pumping power, the coating Q factor, the pumping beam radius, and the cell radius. This difference is explained by the fact that the two curves are associated with different physical processes: the narrow curve characterizes the distortion caused by the magnetic field in the atomic polarization accumulated during multiple passages through the pumping beam after almost nondepolarizing collisions with the coating, while the broad curve corresponds to the distortion of the polarization formed during a single passage through the beam.     

Enhancement of photoinduced polarization rotation in azobenzene polymer films

In this paper we demonstrated enhancement of photoinduced polarization rotation for improved transmission of laser light at low input intensities through a crossed polarized system. It is achieved by utilizing two azobenzene doped polymer thin films in tandem. As the input beam propagates through the films, its polarization rotation induced by each film is additive. We obtained polarization rotation of as much as 24° resulting in enhanced transmission compared to a single-film approach. In addition, this novel design is promising for use as a broadband nonlinear transmission system.     

Focusing properties of concentric piecewise cylindrical vector beam

The focusing properties of a concentric piecewise cylindrical vector beam is investigated theoretically in this paper. The beam consists of three portions with different and changeable phase retardation and polarization. Numerical simulations show that the evolution of the focal shape is very considerable by changing the radius and polarization rotation angle of each portion of the vector beam. And some interesting focal spots may occur, such as two- or three-peak focus, dark hollow focus, ring focus, and two-ring-peak focus. Corresponding gradient force patterns are also computed, and novel trap patterns, including cup shell shape trap with one trap at its each side along axis, rectangle shell shape trap with one trap at its each side, dumbbell optical trap, spherical shell optical trap, may occur, which shows that the concentric piecewise cylindrical vector beam can be used to construct controllable optical tweezers.     

激光偏振编码制导中铌酸锂晶体编码技术研究

针对激光驾束制导系统光束能量调制方式的原理缺陷,讨论了用铌酸锂晶体的电光效应实现空间偏振编码的原理。对铌酸锂晶体的电光效应进行了理论分析,在此基础上设计了基于普科尔效应的空间偏振编码调制器。确定了X轴方向加电场的最佳运用方式,使得经过编码器后的线偏振光具有理想的偏振态梯度分布。对接收数据处理方式进行了讨论,得到了差和比方式对旋转不敏感的结论。在实验室中用可见光进行了近场实验,获得了从最上方近似右旋圆偏振光到中间的线偏振光再到最下方的左旋圆偏振光的偏振态分布。实验曲线表明获得了与理论计算基本一致的结果。     

基于偏振分束成像的旋光角度场测量技术

 为了精确地测量旋光效应中偏振光的旋光角度及其分布,提出了基于偏振分束成像的旋光角度场测量新方法。分析和推理论证了旋光角度场测量理论基础,设计构建了光电检测验证系统,即根据偏振光分束原理,借助于高清晰度CCD采集图像,由计算机对图像进行中值滤波和基于奇异值的匹配处理,再采用“差除和”信号处理以消除光源波动的影响,得到检测结果。实验结果表明,与传统的测量方法相比,该方法不受光源波动的影响,能精确、快速地检测旋光角度二维分布场,并具有很好的线性,数据的均方差仅为传统测量方法的40%。     

基于光偏振旋转效应的碱金属气室原子极化率测量方法及影响因素分析

利用原子自旋效应能够实现超高灵敏度的惯性和磁场测量。一类操控原子自旋处于无自旋交换弛豫态的器件可以进行物理参数测量。碱金属气室为该类器件的敏感表头。碱金属原子密度与原子极化率是碱金属气室的重要参数,对研究原子自旋处于无自旋交换弛豫态有着重要的作用。光的偏振效应在量子计算和原子物理研究中发挥了重要作用。利用光的偏振效应能够实现对碱金属原子密度与原子极化率的检测。提出一种基于光偏振旋转效应的碱金属原子极化率测量方法。首先对碱金属气室加恒定磁场,利用激光作为检测光,根据光偏振旋转原理,检测通过气室的偏振光的法拉第旋转角,得到碱金属气室原子密度。然后将碱金属原子抽运,利用激光作为检测光,检测通过气室的偏振光的偏转角,得到碱金属原子极化率。该方法在测量原子极化率的过程中也测量了碱金属原子密度,实现利用一套系统测量两个重要参数,具有快速测量和高灵敏度等特点,简化了实验设备及过程。对两种偏转角进行仿真分析,得到该方法实验时检测激光波长变化对偏转角的影响,根据仿真图得到检测激光波长的可取范围,验证了该方法的可行性。最后分析激光器波长波动与磁场波动对其测量精度的影响,提出实验对激光器与磁场的要求。     

High-damage-threshold static laser beam shaping using optically patterned liquid-crystal devices

Beam shaping of coherent laser beams is demonstrated using liquid crystal (LC) cells with optically patterned pixels. The twist angle of a nematic LC is locally set to either 0 or 90° by an alignment layer prepared via exposure to polarized UV light. The two distinct pixel types induce either no polarization rotation or a 90° polarization rotation, respectively, on a linearly polarized optical field. An LC device placed between polarizers functions as a binary transmission beam shaper with a highly improved damage threshold compared to metal beam shapers. Using a coumarin-based photoalignment layer, various devices have been fabricated and tested, with a measured single-shot nanosecond damage threshold higher than 30?J/cm2.     

Quantum communication exploiting above threshold OPO intensity correlations and polarization encoding

We present a continuous variable quantum communication protocol based on bright continuous-wave twin-beams generated by a type-II OPO. Intensity correlation between the beams is used in conjunction with a binary randomization of polarization to guarantee security and reveal eavesdropping actions. The scheme presented is asymmetric. Bob (the receiver) retains one of the beams and sends the other one to Alice after a random rotation of its polarization. The cryptographic key elements are encoded through amplitude modulation by Alice, who sends back her beam to Bob after a second rotation of the polarization. Eventually, the beams are detected by Bob after a further random polarization rotation. The security of the system and the possibility of revealing the eavesdropping action in the case of an individual attack are demonstrated by evaluating the bit error rates.     

Instrument for determining the polarization state of reflected and transmitted light

An instrument is described which enables the state of polarization of a light beam to be found. It is discussed with reference to studies of optical rotation, circular dichroism and conventional ellipsometry. The main features are that it records automatically and allows the azimuth and ellipticity of an elliptically polarized beam to be measured simultaneously over a wide wavelength range. The performance is illustrated by spectra showing the optical rotation and circular dichroism of an octahedral cobalt lll species.     

左手材料中圆偏振光束的反常旋转特性研究

根据Whittaker标量势理论,建立了圆偏振光束的矢量传输模型.基于这一模型研究了圆偏振光束在左手材料中的反常旋转特性.通过分析光束偏振态、衍射对强度质心旋转特性的影响,发现圆偏振光束在左手材料中旋转方向反转并揭示其旋转角等于古伊相.采用分析横向能流的方法,揭示左手材料中反向的横向能流是导致反常旋转特性的主要原因.对圆偏振光束在左手材料中反常旋转特性的研究,有利于增强对左手材料中光束传输特性的认识. 关键词： 左手材料 圆偏振光束 旋转特性     

Polarization manipulated solid-state lasers with crystalline-orientations

The polarization states of 〈111〉-cut Yb:YAG crystal microchip lasers were investigated by pumped with the elliptically polarized pump beam from fiber-coupled laser-diode. The manipulated polarized lasers were achieved in laser-diode pumped Yb:YAG microchip laser by controlling the crystalline-orientations in 〈111〉-growth Yb:YAG crystal. Generally elliptically polarized lasers were obtained in laser-diode pumped Yb:YAG microchip lasers. However, crystalline-orientation manipulated linearly polarized laser was obtained when six different sites with different crystalline orientations were set to parallel to the major axis direction of the elliptically polarized pump beam. Six different sites in Yb:YAG crystal were separated with 30° and 90°, which were responsible for the linearly polarized laser oscillations. Circularly polarized lasers were observed when a Yb:YAG crystal was aligned to a special position between two sites responsible for linearly polarized laser oscillation. Effects of the polarization states of pump source on the laser polarization states of Yb:YAG microchip lasers and polarization direction of different polarized lasers with respect to Yb:YAG crystal rotation was addressed.     

Optimization of the design for beamline with fast polarization switching elliptically polarized undulators

Fast switching of X‐ray polarization with a lock‐in amplifier is a good method for acquiring weak signals from background noise for X‐ray magnetic circular dichroism (XMCD) experiments. The usual way to obtain a beam with fast polarization switching is to use two series of elliptically polarized undulators (tandem twin EPUs). The two EPUs generate two individual beams. Each beam has a different polarization and is fast switched into the beamline. It is very important to ensure that the energy resolution, the flux and the spot size at the sample of the two beams are equal in XMCD experiments. However, it is difficult in beamline design because the distances from the two EPUs to the beamline optics are different and the beamline is not switchable. In this work, a beamline design without an entrance slit for fast polarization switching EPUs is discussed. The energy resolution of the two beams can be tuned to be equal by minor rotation of the optics in the monochromator. The flux of the two beams can be balanced through separation blades X, Y in the exit slit, and by adjusting the position of the X blades along the beam. The spot size of the two beams can be adjusted to be equal by shifting the sample as well.     

Arbitrary direction incident Gaussian beam scattering by multispheres

Based on spherical vector wave functions and their coordinate rotation theory,the field of a Gaussian beam in terms of the spherical vector wave functions in an arbitrary unparallel Cartesian coordinate system is expanded.The beam shape coefficient and its convergence property are discussed in detail.Scattering of an arbitrary direction Gaussian beam by multiple homogeneous isotropic spheres is investigated.The effects of beam waist width,sphere separation distance,sphere number,beam centre positioning,and incident angle for a Gaussian beam with two polarization modes incident on various shaped sphere clusters are numerically studied.Moreover,the scattering characteristics of two kinds of shaped red blood cells illuminated by an arbitrary direction incident Gaussian beam with two polarization modes are investigated.Our results are expected to provide useful insights into particle sizing and the measurement of the scattering characteristics of blood corpuscle particles with laser diagnostic techniques.     

Rotation of a Fine Particle with Circularly Polarized Anti-Parallel Collinear Laser Beams

We have succeeded in the operation of rotating a fine particle which was held without mechanical contact by circularly polarized laser beams with opposite propagation directions. A polystyrene latex particle 11.9 μm in diameter deformed in a disk-like shape was dispersed in water, and was trapped using the anti-parallel collinear laser beams which were set up so that they had the circular polarization rotating in the same direction. It was observed that the trapped particle rotated in the same direction as the rotation of the circular polarization of light. Inversion of the rotational direction of the circular polarization of light reversed the direction of the rotation of the particle. Although the rotational speed of a particle varied significantly from particle to particle, it was found to be proportional to the laser beam intensity. A typical value for the rotational speed per beam intensity was 2.1 Hz/W.     

Focus shaping of cylindrically polarized vortex beams by a high numerical-aperture lens

The focus-shaping technique of a cylindrically polarized vortex beam by a high numerical-aperture lens is reported. Such a polarized vortex beam is decomposed into radial and azimuthal polarization. It is shown that the total intensity distribution in the focal region is dependent not only on the numerical-aperture maximal angle and the polarization rotation angle but also on the topological charge. By choosing the proper combination of parameters, the adjustably confined flat-topped focus and focal hole can be obtained. The focus-shaping technique may find wide applications, such as optical tweezers, laser printing and material processing.     

相位板偏振偏转角对径向偏振光的梯度力分布的影响

 研究了同心分区偏振偏转相位板对径向偏振光梯度力的调制效应。给出了相位板各部分偏振偏转角不同时,光学梯度力的分布情况。模拟结果表明:随着同心分区相位板各部分的半径和偏振旋转角的改变,光学梯度力方向及大小明显变化,且会产生许多可控的梯度力分布模式,可应用于微粒的收集、分离和合并。结果显示同心分区相位板对径向偏振光的调制可以用来生成可调光镊。     

Evolution of polarization in an inhomogeneous isotropic medium

The depolarization and rotation of the polarization plane of radiation propagating in a two-dimensional graded-index medium is investigated on the basis of the quantum-mechanical method of coherent states. It is shown that the degree of polarization of both linearly and circularly polarized radiation decreases with increasing distance as a result of interaction between the polarization (spin) and the path (orbital angular momentum) of the beam. The wave nature of the depolarization is emphasized. The depolarization decreases as the radiation wavelength decreases. It is found that the degree of polarization exhibits oscillations of pure diffraction origin during the propagation of light in a single-mode optical fiber. It is shown that the rotation of the polarization plane is nonuniform in character and depends on the offset and the tilt angle of the incident-beam axis relative to the fiber axis. The Berry phase is found to undergo oscillations of a wave nature during the propagation of radiation in an inhomogeneous medium. It is shown that the spread in the angle of rotation of the polarization plane increases with distance and can be determined from measurements of the degree of polarization of the radiation. Zh. éksp. Teor. Fiz. 112, 1985–2000 (December 1997)