沙尘气溶胶粒子群的散射和偏振特性

根据Mie散射理论,以对数正态分布函数描述沙尘气溶胶粒子群的粒径尺度分布,计算了沙尘气溶胶粒子群在0.2～40μm波段间对太阳短波辐射和地球大气长波辐射的单次散射反照率、散射相矩阵函数,揭示了不同相对湿度时,沙尘粒子群对入射辐射的散射和偏振的特征。结果表明,沙尘粒子群的单次散射反照率随着入射波长的增加有较大起伏,不同相对湿度条件下,变化趋势基本一致;在可见光、近红外波段单次散射反照率随湿度增加而变大,湿度95%时非常接近于1;大于10μm的热红外波段单次散射反照率随相对湿度增加而减小,具有较强的吸收辐射能力。散射辐射强度受湿度影响较小,随散射角的增加呈现先减小后增大的趋势,且增大的趋势随着波长的增加而减弱;不同波段上,线偏振和圆偏振随散射角和相对湿度变化存在差异;在前向和后向仅对入射辐射为圆偏振辐射产生圆偏振散射;散射光的偏振特性及其湿度差异主要表现在后向散射区,多以拱形形式体现。拱顶峰值散射角位置存在差异,且峰值散射角随相对湿度的降低向后向漂移。     

不同波长的散射介质后向散射光偏振度特性

基于Stockes矢量,通过测量以线偏振光和圆偏振光入射时脂肪乳剂后向散射光的偏振度,研究了532nm、650nm和780nm三个波长的光与散射粒子粒径为325nm的脂肪乳剂溶液作用后,其后向散射光的偏振度特性.研究结果表明,对于入射线偏振光,780nm波长后向散射光中的线偏振光成分多于圆偏振光成分,而532nm波长则相反;对于入射圆偏振光,三个波长后向散射光中的圆偏振光成分均多于线偏振光成分;532nm波长的总偏振度高于650nm和780nm两个波长各自的总偏振度;线偏振光的保偏性优于圆偏振光的保偏性,但偏振光在散射介质中的穿透深度较小.因此,后向散射成像技术适用于物体表层成像,而且选择波长略大于粒径的线偏振光可以提高成像质量.     

不同波长的散射介质后向散射光偏振度特性

基于Stockes矢量,通过测量以线偏振光和圆偏振光入射时脂肪乳剂后向散射光的偏振度,研究了532 nm、650 nm和780 nm三个波长的光与散射粒子粒径为325 nm的脂肪乳剂溶液作用后,其后向散射光的偏振度特性.研究结果表明,对于入射线偏振光,780 nm波长后向散射光中的线偏振光成分多于圆偏振光成分,而532 nm波长则相反;对于入射圆偏振光,三个波长后向散射光中的圆偏振光成分均多于线偏振光成分;532 nm波长的总偏振度高于650 nm和780 nm两个波长各自的总偏振度;线偏振光的保偏性优于圆偏振光的保偏性,但偏振光在散射介质中的穿透深度较小.因此,后向散射成像技术适用于物体表层成像,而且选择波长略大于粒径的线偏振光可以提高成像质量.     

X射线荧光CT成像中荧光产额、退激时间、散射、偏振等关键物理问题计算与分析

X 射线荧光 CT(X-ray fluorescence computed tomography,XFCT)是一种使用X射线荧光(X-ray fluorescence,XRF) 实现功能性成像的新技术,在生物医学成像中表现出较大潜力.但是,X射线穿过生物体的同时还会产生大量康普顿散射光子,对XRF信号的采集形成很强的背景噪声;因此,如何有效消除康普顿散射噪声对于提高XFCT成像质量至关重要.本文研究总结了 XFCT成像过程中涉及的物理过程,包括:荧光的产额、退激发时间、荧光发射角分布、荧光偏振态、康普顿散射角分布与散射光偏振态,并通过研究荧光与散射光物理性质的差异寻找去除康普顿散射噪声的方法.经过物理过程推导和分析计算,发现:1)高原子序数元素的K层荧光退激发时间极短,在现有探测器的时间分辨率条件下,无法分辨散射光与荧光;2) K层发射荧光的角分布各向同性,康普顿散射角分布在与入射光偏振方向附近取得最小值,而且入射光线偏振度越高,散射光的微分截面越小,偏振光源将有利于减少康普顿散射噪声;3) K层荧光线偏振度为零,而康普顿散射光子在一些散射方向上具有一定线偏振度,因此偏振态的差异可能用于降低康普顿散射噪声.     

光在可变厚度介质中后向散射传输的偏振特性分析

针对不同浓度下介质厚度改变对后向散射光偏振特性影响的问题,以典型蒙特卡罗偏振模型为基础,提出了一种基于后向散射的可变介质厚度蒙特卡罗偏振模型。根据本文提出的模型开展了仿真实验,得到了不同浓度下介质厚度与后向散射偏振特性的影响关系。仿真结果表明,介质厚度在不同浓度下均对后向散射光的偏振度有着直接影响;在低浓度的情况下,介质厚度增加主要起消偏作用,浓度达到一定阈值后,介质厚度增加起起偏作用;在低浓度的情况下,线偏振光的后向散射光偏振保持特性优于圆偏振光,浓度达到一定阈值后,圆偏振光的后向散射光偏振保持特性优于线偏振光;在浓度极高的情况下,线偏振光与圆偏振光的保持特性趋于一致。     

红外区磷化稼散射强度的计算与分析

根据Mie散射理论,对磷化稼粒子光散射特性进行了数值计算与理论分析,得到了散射强度与散射角、入射波长以及偏振度与散射角的关系。研究表明,红外波段光散射很小,前向散射占有优势,粒子半径越大,前向散射越强,并且在散射角900方向上能观测到线偏振光,对研究GaP红外光学特性提供了理论参考。     

混浊介质中线偏振光和圆偏振光的后向漫散射特征

以标准的组织模型Intralipid脂肪乳溶液为研究对象,采用CCD偏振成像系统,通过测量该混浊介质的后向漫散射光的斯托克斯矢量,深入研究了不同方位的线偏振光及不同旋向的圆偏振光入射时,后向漫散射光的特征.研究结果表明：对不同的入射偏振态,后向漫散射强度、偏振度的空间分布具有方位选择性,强度和偏振度的大小随距离入射点的距离增加而减小;介质浓度增加,后向散射强度增加,偏振度减小,且同一浓度下,圆偏振光的偏振度总是高于线偏振光.     

复合金属粒子散射强度分布的计算与分析

根据Mie散射理论,对金银复合粒子的散射强度和偏振度进行了数值计算与理论分析,得到了散射强度、偏振度与散射角、入射波长及核壳大小之间的关系。结果表明,入射波长越大,前向散射越强,易出现线偏振光;而核壳半径越大,背向散射越弱,易出现退偏振现象。该结论对金银复合材料光学特性方面的开发和应用提供理论参考。     

烟雾浓度对偏振光传输特性的影响

针对烟雾环境中烟雾浓度对偏振光传输特性的影响问题,采用烟煤粒子作为研究对象,分别研究了水平、垂直、+45°方向线偏振光及左旋、右旋圆偏振光经不同浓度介质传输后偏振度(DOP)的变化情况。采用蒙特卡罗方法建立仿真模型并对偏振传输理论进行分析。根据实测中浓度条件的不可控因素,采用光学厚度表征浓度,从仿真与室内实验两方面验证浓度对偏振光传输特性的影响。结果表明,偏振光入射时,偏振度随介质浓度的增加不断下降;水平、垂直、+45°线偏振光入射时,不同线偏振光偏振度随浓度的变化趋势大致相同;圆偏振光入射时,左旋、右旋圆偏振光的变化趋势基本一致;介质浓度较低时,圆偏振光偏振度随浓度的变化与线偏振光大致相同,而介质浓度较高时,圆偏振光的偏振度始终大于线偏振光,表明圆偏振光在高介质浓度、低能见度条件下具有更好的保偏能力。     

湿度影响下的气溶胶粒子的偏振特性

气溶胶散射特性对大气辐射和气候研究具有重要意义。为研究气溶胶在不同相对湿度下的散射特性,根据Mie散射理论建立了湿度偏振模型,在0.55μm的可见光下,分析比较了3种气溶胶的单粒子和粒子群在不同相对湿度下的偏振特性。结果表明,相对湿度变化对气溶胶偏振度有规律性的影响,尤其在120°～150°的后向散射角区域,3种粒子偏振度都随相对湿度的增大而增大,说明了部分后向散射角上散射光偏振度能有效反映气溶胶粒子随相对湿度变化的信息。     

Spectral Dependence of Quasi-Rayleigh Polarization Leap of Nonspherical Particles: Polystyrene Beads Application

Solid particles in Earth’s atmosphere, such as polystyrene beads, are an important factor affecting the processes of absorption and scattering of light in the atmosphere. These processes affect on the solar energy transfer in the Earth’s atmosphere, consequently they have influence on the regional and global climate changes and atmospheric visibility. In particular, great interest to study the scattering properties of small particles compared with wavelength, because of such particles experience low gravitational settlement and may have long time of life in the atmosphere. When scattering particle is much smaller than the wavelength of the scattered or absorbed light, this is the case of Rayleigh scattering. Scattering properties of these particles (such as intensity and the degree of linear polarization) at the Rayleigh scattering are simply derived from electromagnetic Maxwell’s equations. But when the particles are large enough to be comparable with the wavelength, the deviations from Rayleigh scattering law are observed. One of the clear manifestations of such deviations is the recently discovered quasi-Rayleigh polarization leap of monodisperse spherical particles. This quasi-Rayleigh polarization leap allows remote sensing of the sizes of distant particles, based on the spectral position of quasi-Rayleigh polarization leap at different phase angles of observation. In this paper, we studied the effect of the non-sphericity of a scattering polystyrene particle on the magnitude and position of the quasi-Rayleigh polarization leap. It is established that the non-sphericity shifts the position of the quasi-Rayleigh polarization leap shorter wavelengths. It is shown that for non-sphericity of particles makes the quasi-Rayleigh polarization leap becomes less pronounced. Moreover, it was found, that increasing of the phase angle and degree of non-sphericity shift the quasi-Rayleigh polarization leap position to shorter wavelength. However, in the case of not very elongated particles, the quasi-Rayleigh polarization leap is quite well manifested. Therefore, this method is suitable for remote sensing not only the size, but also the degree of non-sphericity of the scattering particles. A simple formula has been obtained for polystyrene beads that relates the degree of non-sphericity of a particle with the wavelength and phase angles at which the quasi-Rayleigh polarization leap is observed.     

低太阳高度角条件下的天空偏振模式模拟及大气折射影响研究

为模拟低太阳高度角条件下的天空偏振模式,自主开发了考虑大气球形几何及大气折射效应的辐射传输模式VSPART,并将其运用于漫射光偏振特性仿真.在模式中,基于射线追踪法实现了光线传播轨迹的追踪和入射光偏振态及透过率的计算,基于矩阵算法实现了辐射传输方程的求解.将VSPART模拟结果与基准值、SPDISORT模拟值进行了比较,验证了模型的准确性.在瑞利散射大气和含气溶胶大气条件下,模拟并分析了漫射光偏振度及偏振方向的分布特征,讨论了大气球形几何及折射效应对天空偏振度的影响.结果表明,低太阳高度角条件下,随着波长增加,瑞利散射大气对应的偏振度整体随之增强,中性点向大天顶角方向移动;气溶胶的存在并不改变天空偏振度分布特征,但对偏振方向影响显著,随着光学厚度的增加,天空偏振度值迅速降低;中性点的偏移可能与低阶散射过程紧密相关;大气球形几何和折射效应的主要影响区域为地平线区域、两中性点附近及天顶区域;瑞利散射大气条件下,随着波长增加,大气球形几何及折射效应的影响逐步减弱,特别在中性点附近及天顶区域,其影响逐步消失;随着气溶胶光学厚度的增加,其影响随之增强.     

Polarization fluctuations of single photon states in a slant channel with non-Kolmogorov turbulence

Polarization properties of single photon states propagating through the non-Kolmogorov turbulence in a slant channel are studied based on the degree of polarization of quantum field. The degree of polarization of single photon states for linearly polarized quantum beam propagation in a slant turbulent channel are developed. Our results show that the effects of the outer scale fluctuations of atmospheric turbulence and the wavelength difference of the beams on the polarization can be ignored and the smaller inner scale of turbulence and larger zenith angle of communication channel will lead to larger fluctuations of the polarization of single-photon states. The effects of the inner scale of turbulence on polarization of single photon states are more significant for bigger refractive-index power and bigger zenith angles.     

生物组织多光谱偏振特性研究

生物组织内部结构复杂且具有较强的散射特性,而光作为生物组织检测的重要信息载体,其自身特性包括颜色、幅值、偏振等都对信息获取有较大的影响.结合偏振成像,对生物组织多光谱偏振特性展开了研究,依据不同微粒尺寸的分布建立了均匀单层生物组织模型,结合瑞利和米氏散射理论模拟了基于单个微粒的两种散射事件.瑞利散射具有较好的前向后向散...     

Influence of single scattering and multiple scattering on backscattered Mueller matrix in turbid media

Monte Carlo algorithm and Stokes-Mueller formalism are used to simulate the propagation behavior of polarized light in turbid media. The influence of single scattering and multiple scattering on backscattered Mueller matrix in turbid media is discussed. Single and double scattering photons form the major part of backscattered polarization patterns, while multiple scattering photons present more likely as background. Further quantitative analyses show that single scattering approximation and double scattering approximation are quite accurate when discussing the polarization patterns near the incident point.     

Polarimetric characterization of ultra-high molecular weight polyethylene (UHMWPE) for bone substitute biomaterials

In this work the UHMWPE is characterized for their optical properties with Mueller matrix polarimeter. The transmittance birefringence, retardance, polarizance, linear and circular polarization and absorbance of polarized light at different wavelengths ranging 400-800 nm are measured. The presented Mueller matrix elements along with depth resolve polarization decrease in intensity with the change in the wavelength. Linear retardance increases compared to circular through highly scattering polyethylene. High refractive index and low mean free path; and close bonding of particles of material rotates the incoming photons and circular polarization which is dominant as compared to the linear one. Therefore the average intensity increases with both the optical depth and the scattered concentration in UHMWPE, which would accordingly decrease the apparent degree of polarization.The extracted results in terms of linear and circular retardances prove that UHMWPE is compatible, strong, and compact. This research work provides an optical characterization technique for bone substitute biomaterial in the health care industry.     

基于色散偏振度的乳化油光谱检测系统研究

以色散偏振光谱检测技术为背景,着重研究了乳化油颗粒的偏振光学特性及米散射物理模型,构建了色散偏振度光谱检测系统。在400～700 nm波长范围内,分别对四种样品进行了301个波段的光谱反射率采集。结合贝塞尔函数和汉克尔函数,推导出了入射光波长与散射光偏振振幅矢量的关系,提取了一个新的特征参数：色散偏振度（DODP）。在暗室条件下,对乳化油样品ND18和ND75进行测量,利用色散偏振公式计算出了样品在各测量波长处的偏振度值,验证了基于DODP值检测乳化油的可行性。研究发现,虽然米散射的解是由单个球体的衍射推导而来,但是只要它们的直径和组成相同,且彼此之间的距离比波长大,也同样可以用于任意数量的球的衍射。在这种情况下,被不同球体散射的光之间没有相干的相位关系,总散射能量等于被一个球体散射的能量乘以它们的整数。当观测平面与入射波电矢量振动方向之间的夹角Φ=0或者Φ=π／2时,散射光分量E(s)_θ或者E(s)_Φ消失。由于ND18的粒径比ND75的粒径小,所以ND18的前向散射波瓣较大,前向散射与后向散射的比值较小。在相同光照条件下,ND75的多次散射现象要比ND18严重。根据路径相关矩阵的理论,多次散射容易引起退偏振,二次辐射波会在角域内扩散和分布。因此,被测乳化油表面产生的散射次数与入射光能的阻尼能力成正比。由于乳化油表面入射光的能量耗散存在差异,因此能量耗散率与入射波矢量方向的前向散射振幅的分量成正比,且乳化油的偏振散射程度不同于入射光的偏振散射程度。实验结果表明,DODP可以反映出乳化油由多次色散引起的去偏振能力。由于模拟光源是自然光,所以计算散射光的偏振参数非常方便,可以大大缩短数据处理时间,减小实验误差。DODP不仅能够识别海水中的乳化油,而且能够区分不同浓度的污染物,准确识别出乳化油的边缘扩散。     

Splitting of a polarized photon by an unpolarized electron

The process of splitting of a polarized photon of a plane electromagnetic wave into two polarized photons by an unpolarized electron is examined. The degree of circular and linear polarization of the photon radiated is studied in detail.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 133–138, August, 1978.The authors are grateful to Professor V. G. Bagrov for discussing the research.     

Photon polarization as a probe for quark–gluon plasma dynamics

Prospects of measuring polarized photons emitted from a quark–gluon plasma (QGP) are discussed. In particular, the detection of a possible quark spin polarization in a QGP using circularly polarized photons emitted from the plasma is studied. Photons leave the QGP without further interaction and thus provide a primary probe for quark polarization within the QGP. We find that photon polarization cannot solely arise due to a possible QGP momentum space anisotropy, but may be enhanced due to it. In particular, for oblate momentum distributions and high photon energies, quark polarization is efficiently transfered to photon polarization. The role of competing sources of polarized photons in heavy-ion collisions is discussed.