Polarization studies of radiation emitted by surface plasmons in silver

Measurements are reported on the polarization of radiation emitted by the roughness induced decay of nonradiative surface plasmons optically excited by light in thin Ag films. This radiation is of mixed polarization when the incident light is p-polarized. The s-polarized component of the radiation is observed to be considerably less intense than the p-polarized component.     

Anomalous polarization effects during light scattering in random media

The dependence of the intensity of light backscattered from a layer of a randomly inhomogeneous medium on the polarization of incident light and the size of scatterers has been investigated. The results of numerical simulation have demonstrated that the direction of rotation of the plane of polarization is different in systems with small- and large-scale inhomogeneities. It is shown for the first time that the dependence of the sign of the residual circular polarization on the size of scatterers can be observed in systems described by the Henyey-Greenstein phase function used in simulating biological tissues. A similar anomalous polarization effect, which consists in changing the direction of rotation of the plane of polarization of backscattered light with an increase in the scattering angle, is revealed in studying the coherent backscattering component. These polarization effects are observed in light backscattering from optically active media.     

Bragg diffraction of light by ultrasonic shear waves in a plane-parallel layer

We have studied anisotropic Bragg diffraction of light by ultrasonic shear waves in an optically isotropic plane-parallel layer. We have established the analytical dependences of the relative intensities and polarization azimuths of reflected and transmitted diffracted waves on the intensity of the ultrasound, the layer thickness, the angle of incidence, and the polarization azimuth of the incident light. We show that rotation of the plane of polarization of the diffracted wave is determined by the different Fresnel reflection of the s and p polarized components of the incident light in the plane-parallel layer. We have determined that in mismatched acousto-optic structures, deep amplitude modulation of transmitted and reflected light is possible which is an order of magnitude greater than the usual modulation in matched structures.     

光学元件残余偏振测量方法与装置

光学镜头的残余偏振是影响偏振遥感探测、偏振军事目标识别和精密光学测量仪器测量准确度的一个关键参数。针对大口径可见光波段光学镜头偏振度准确测量的问题,研制了一台光学镜头残余偏振度测量装置。该装置利用表面镀金属膜的大口径离轴抛物面反射镜作为准直光源,通过控制入射光的入射角、降低入射光源的残余偏振度等技术,在水平、垂直、45°、135°的方向获得了一致性很高的斯托克斯参量。为了验证该装置的性能,对可见光波段口径小于160 mm的光学镜头残余偏振进行了实际测量,测量结果表明,该测量装置的残余偏振度低于0.2%,可满足高精度光学镜头残余偏振的测量需要。     

Simultaneous acquisition of all four forms of circular polarization Raman optical activity: results for α‐pinene and lysozyme

A new circularly polarized (CP) Raman spectrometer is described that demonstrates simultaneous acquisition of all four forms of circular polarization Raman optical activity (ROA). The instrument is a design extension of a commercially available back scattering circular polarization (SCP) ROA spectrometer. Circular polarization of the incident beam is introduced with a quarter‐wave plate, and a half‐wave plate alternately positioned in and out of the beam controls the modulation between right circular polarization (RCP) or left circular polarization (LCP) states. Combining this modulation with the simultaneous detection of RCP and LCP scattered Raman radiation allows the measurement of incident circular polarization (ICP), SCP, in‐phase dual circular polarization(DCP_I) and out‐of‐phase DCP_II‐ROA. In addition, three different forms of backscattered Raman spectra, namely unpolarized, highly polarized, and depolarized Raman spectra, as well as a degree of circularity spectrum are obtained. The performance of the new all‐CP ROA spectrometer is evaluated with neat α‐pinene and aqueous hen lysozyme solution. Copyright © 2011 John Wiley & Sons, Ltd.     

Simple parametric representations of the polarization optical properties of birefringent biological tissues in reflection polarization spectroscopy

The use of polarization reflection spectroscopy for investigating complex scattering media, including orientationally ordered optically anisotropic elements, requires a special choice of output parameters (represented by spectra) that characterize polarized light scattering by objects under study because the standard characteristics, such as the Mueller matrices, depend on the azimuthal orientation of the medium. We propose compact and convenient sets of experimentally determined output parameters that involve separate detection of co- and cross-polarized components of light scattered by a sample irradiated by a normally incident linearly polarized beam and include characteristics invariant with respect to the azimuthal rotation of the sample.     

Simple depolarizers for spectrophotometric measurements of anisotropic samples

Spectrophotometric measurements on optically anisotropic samples are considerably affected by the partial polarization of light in the instrument. It is shown that by depolarizing the incident beam, more realistic results are obtained even for strong directional anisotropic materials. Two types of depolarizers were investigated.     

Circular differential double diffraction in chiral media

In an optically active liquid the diffraction angle depends on the circular polarization state of the incident light beam. We report the observation of circular differential diffraction in an isotropic chiral medium, and we demonstrate that double diffraction is an alternate means to determine the handedness (enantiomeric excess) of a solution.     

T-matrix approach to calculating circular polarization of aggregates made of optically active materials

Optical activity is a typical property of the biological materials where left-handed amino-acids and right-handed carbohydrates dominate (so called homochirality). Observationally, optically active materials reveal themselves through the circular polarization in the light they scatter. Thus, circular polarization produced by the optically active particles can serve as a biomarker. It is known that biological (e.g. colonies of bacteria) and pre-biological (e.g. dust in comets) particles often have a complex structure that can be modeled presenting them as aggregates of small monomers. This motivated the development of the T-matrix code presented in this paper, which enables calculation of the scattering matrix - including circular polarization - of the light scattered by aggregated optically active particles. The code can be used for modeling the light scattering by biological objects (e.g. colonies of bacteria, blood cells) and for interpretation of the circular polarization produced by the cosmic dust that contains (pre)biological organic, e.g. comet dust or planetary aerosols.     

Backscattering of linearly and circularly polarized light in randomly inhomogeneous media

The scattering of linearly or circularly polarized light from a semibounded randomly inhomogeneous medium is considered. A new technique for simulating the electromagnetic radiation transport using the Monte Carlo method is proposed, which makes it possible to avoid cumbersome calculation of Muller matrices. Expressions are obtained for the co- and cross-polarized components of backscattered light for incident light of arbitrary polarization. The coherent and incoherent backscattering components are calculated for arbitrary combinations of incident and scattered light polarizations. It is shown that the main contribution to coherent backscattering is from the co- and cross-polarized components for linearly and circularly polarized light, respectively. The backscattering from an optically active random medium is calculated.     

Bispectral Circular Dichroic Coding Metasurfaces

The frequency-dependent circular dichroism is proposed to extend the wave manipulating capability of coding metasurfaces. As a proof of concept, the bispectral circular dichroic coding metasurfaces (CDCMs) are realized using circular dichroism resonators (CDRs) implemented via introducing loss resistors into the circular polarization conversion resonators. The CDRs are distinguished into left-handed CDRs and right-handed CDRs. Left-handed CDRs absorb left-handed circularly polarized (LCP) wave and convert right-handed circularly polarized (RCP) wave into LCP wave. Conversely, they are defined as right-handed CDRs. Two bispectral CDRs are designed with the left-handed (right-handed) and right-handed (left-handed) working bands in 7–8.5 and 22.2–22.5 GHz, respectively. And then, 1 bit bispectral CDCM with 0101…/1010… coding sequence is designed. Simulated results indicate that the designed CDCM strongly absorb the incident LCP (RCP) waves in the frequency region 7–8.5 GHz (22.2–22.5 GHz), but the incident RCP (LCP) waves are anomalously reflected into four beams of the LCP (RCP) waves with high efficiency. The measured results agree well with the simulations. The results in this work may provide an effective solution for the inverse and helicity-dependent manipulation of the electromagnetic waves in two distinct frequency regions.     

分振幅型全Stokes同时偏振成像系统波片相位延迟误差分析

分振幅型全Stokes同时偏振成像仪具有实时性好、空间分辨率高、精度高等优点,有很高的应用价值.分振幅型全Stokes同时偏振成像系统利用偏振分束器、1/2波片和1/4波片将入射光Stokes矢量调制在4幅图像中,可解析入射光Stokes矢量. 1/2波片和1/4波片的相位延迟误差对Stokes矢量测量精度有着不可忽略的影响.建立了包含上述两种误差的Stokes矢量测量误差方程,分析了1/2波片和1/4波片相位延迟耦合误差对自然光、0°/45°线偏光、左旋圆偏光等典型基态入射光的Stokes矢量测量误差的影响,推导了任意偏振态的Stokes矢量测量误差的表征方法.在邦加球球面和球内选取不同偏振度的Stokes矢量作为入射光进行仿真.结果表明, Stokes矢量测量误差和偏振度测量误差均随着入射光偏振度的增大而增大.选取入射光偏振度为1时的偏振测量精度评估系统.为满足2%的偏振测量精度, 1/2波片相位延迟误差应在±1.6°内, 1/4波片相位延迟误差应在±0.5°内.这对提高系统的偏振测量精度具有重要意义,为系统设计和研制提供了重要的理论指导.     

转换反射中光自旋霍尔效应的自旋堆积方向

从理论上和实验上研究了转换反射中光自旋霍尔效应的自旋堆积方向的方法,建立了描述光束在空气-棱镜界面反射的自旋堆积模型,揭示了横移与光束入射偏振角的定性关系。研究发现,当入射角小于布儒斯特角时,随着入射偏振角的逐渐增大,自旋堆积的方向发生反转。而当入射角大于布儒斯特角时,自旋堆积的方向不再随入射偏振角的变化而反转。结果表明,在光束入射角为确定值且小于布儒斯特角的情况下,可以通过调控光束的入射偏振角转换自旋堆积的方向。转换自旋堆积方向的研究为有效调控光自旋霍尔效应提供了新的途径。     

快速空间测角系统中偏振像差的分析与研究

快速空间测角系统需要在一定的平移范围内均能实现测量功能,这就要求光束在接收单元具有一定的覆盖面积.受器件尺寸所限,选择对入射光束进行扩束,然而非正入射光经过系统会产生偏振态变化,存在偏振像差,引起测量误差.本文通过采用偏振光线追迹的方法,结合电磁场的边界条件,对快速空间测角系统中一定方位及入射角范围内的光束通过偏振棱镜后出射光束的偏振态变化与分布进行了理论研究及仿真分析;并通过搭建实验平台,利用平移接收单元来模拟不同的入射方位及角度变化.根据实验值与仿真结果的对比分析,得出在方位角为0o时,测量误差较小,在方位角为90o时,测量误差最大,且随平移距离(即入射角)的增大,测角误差增大.验证了偏振像差的存在对系统测角带来的影响及理论分析的正确性,并提出了改进措施.所得研o究结果对优化系统结构并进一步提高系统性能具有一定的指导意义.     

Optically switchable, polarization-independent holographic polymer dispersed liquid crystal (H-PDLC) gratings

An optically switchable, polarization-independent holographic polymer dispersed liquid crystal (H-PDLC) transmission grating is demonstrated by adding azobenzene-LC and chiral molecules into the H-PDLC formulation. The optical switchable mechanism is from the trans-cis photoisomerization of the doped azobenzene-LC, which modulates the refractive index of the LC rich area. The dependence of the diffraction efficiency of the H-DPLC grating without chiral molecules on light polarization suggests that the orientation of LC directors within the droplet is ellipsoidal and uniaxial. However, the addition of chiral molecules into the H-PDLC formulation helps the formation of isotropic and non-uniaxial LC directors within the droplets. The polarization properties of the grating are investigated and analyzed by the coupled and modified coupled wave theory with a model of sinusoidal dielectric modulation. The results show that the addition of chiral molecules changes the LC phase from nematic to chiral-nematic, where the grating efficiency, which is modulated by the photoinduced phase transition, is independent of the polarization of incident light. Our findings may help improve optical systems that utilize non-polarized light.     

Spatial polarization sensitivity of single Au bowtie nanostructures

Metallic bowtie nanostructures as plasmonic nanoantennas can create highly enhanced local fields when resonating with the incident light. With Au bowtie nanostructures fabricated by lithography method, we experimentally observed that the photoluminescence (PL) spatial profile from a single Au bowtie nanoantenna was strongly dependent on the excitation light polarization. While varying the incident light polarization, the spatial distribution of the PL intensity in the nanogap of an Au bowtie changed as predicted by the simulation results on the electromagnetic field enhancement distribution. The polarization feature of the PL intensity relative to the polarization direction of incident excitation light was also discussed. The study may find application in the design of polarization sensitive plasmonic sensors.     

基于表面等离激元的偏振态控制光开关

利用四个Au纳米棒组成的类矩形纳米棒四聚体结构设计了一种基于偏振态控制的光开关,并采用有限元法研究了该结构对入射光偏振态的响应特性.研究发现,该结构的透射光谱对入射光的偏振方向具有很强的依赖性,当入射光的偏振角度变化π/2时,其特征峰的开关比分别能达到27.81dB和21.65dB.分析表明,该结构的开关效应主要由不同偏振态下所导致的水平双纳米棒和竖直双纳米棒之间的近场耦合强度不同而实现,该结构透射系数与偏振角度的关系服从Malus law.此外,通过改变类矩形纳米棒阵列结构参数,研究了结构参数对其光开关响应特性的影响.在此基础上,通过改变阵列的周期参数,研究了入射光水平偏振和垂直偏振下周期参数对单元结构透射光谱的影响.该研究结果能够为可调谐双波长偏振光开关的设计提供理论依据.     

一种高精度偏振遥感探测方式的精度分析

检偏器的角度误差是影响偏振遥感探测精度的重要因素之一,是许多高精度定量化偏振遥感需要考虑的一个问题。在检偏器(0°,60°,120°)放置的测量系统中,当入射光偏振角接近于0°或180°时偏振测量易产生最大误差值,而偏振角接近30°,90°和150°时,偏振度的测量具有很高的精度;在检偏器(0°,45°,90°)放置方式中,偏振角接近45°的光束测量易具有最大误差值,而偏振角接近于0°,90°和135°时,角度误差对偏振度测量精度的影响很小。除了个别偏振角外,对高偏振度入射光束的偏振测量通常具有较大的偏振测量误差。因此,引进线偏振光的平均偏振度测量精度描述偏振测量装置的优劣,结果表明检偏器(0°,60°,120°)放置方式优于检偏器(0°,45°,90°)放置方式。     

Influence of incident light polarization on photonic nanojet

Dielectric microspheres can confine light in a three-dimensional (3D) region called photonic nanojet is shown when they are illuminated by different polarized beams. The influence of incident light polarization on photonic nanojet using the finite-difference time-domain (FDTD) method is demostrated. The axial field intensity profiles of photonic nanojets for both the linear and circular polarization incident beams are very similar. Azimuthal polarization incident beam induces a doughnut beam along the optical axis, while the radial polarization incident beam permits one to reach an effective volume as small as 0.7(λ/n) 3 .     

Polarization properties of single metallic nano-spheroid using 3-D boundary element method

The polarization properties of an individual metallic nano-spheroid illuminated by the linearly polarized light are studied based on 3-D boundary element method. The scattering cross sections and the local field enhancements are investigated in detail when the incident lights are with different polarization directions and wavelengths. The numerical results show that the polarization direction of the incident light can strongly influence the scattering spectrum and the enhanced field distribution of the metallic nano-spheroid. The incident light with polarization direction parallel or perpendicular to the major axis can inspire longitudinal or transversal local surface plasmons resonance modes, respectively. The electric field enhancement and distribution around the nano-spheroid can be conveniently tuned by carefully selecting the polarization direction and wavelength of the incident light.