随机取向非球形沙尘气溶胶粒子的光学特性

利用离散偶极子近似法分析了一种随机取向旋转椭球体沙尘气溶胶粒子模型在尺度参数变化范围为0.1~23时(波长0.55!m对应有效半径为0.01~2!m)的光学特性,研究了沙尘粒子非球形性程度对其光学特性的影响,并考察了非球形粒子的随机取向能否用等体积球体来代替。就随机取向单分散和多分散旋转椭球体沙尘气溶胶而言,粒子非球形特征越明显,消光效率因子、不对称因子和单次散射反照率基本上偏离其等体积球体越大;对于相同的非球形,不对称因子偏离其等体积球体的相对偏差要比消光效率因子和单次散射反照率要大。非球形粒子的随机取向并不能使其光学特性严格等效为其等体积球体的光学特性。如果粒子形状偏离球体较小,则非球形粒子的随机取向的平均效果能使其消光效率因子、不对称因子和单次散射反照率近似用等体积球体的对应光学参量来等效;而如果粒子形状偏离球形较大,仅有单次散射反照率可以近似用等体积球体的单次散射反照率来等效,例如,轴半径比为16的旋转椭球体沙尘粒子的单次散射反照率偏离其等体积球体仅在3%以内。     

典型雾霾粒子及团簇的散射吸湿增长特性

为探究雾霾粒子吸湿性引起的散射吸湿增长特性,基于雾霾粒子湿度增长模型,利用Mie散射理论和多球T矩阵计算方法,详细研究了硫酸、硫酸铵、沙尘、硝酸铵以及碳质气溶胶5种典型雾霾粒子及其团簇在入射波长为532 nm、相对湿度在60%～95%范围内的散射吸湿增长特性。研究结果表明:对单一雾霾粒子,硫酸、硫酸铵以及硝酸铵这类二次水溶性无机粒子及其团簇的散射吸湿增长较突出,沙尘较为平缓,而碳质气溶胶则呈现抑制作用,同时,小粒径粒子的散射吸湿增长因子呈指数增长,而大粒径粒子则呈波动、负增长趋势;对于雾霾粒子的团簇,散射吸湿增长因子曲线整体增幅减小,粒子团簇的体积分数对散射吸湿的影响明显,随着体积分数的增加,散射吸湿增长因子曲线的波动频率增大,同时振幅减小,但整体呈现的吸湿增长还是由团簇粒子的粒径范围与成分决定,其中团簇粒径范围影响较大。这为探究雾霾粒子散射吸湿增长特性和研究大气污染提供了理论支持。     

飞尘气溶胶粒子散射特性分析:对比实验和米散射方法

采用Mie散射理论计算了可见光波段等效球飞尘气溶胶粒子的Stokes散射矩阵,并与实验得到的空间随机取向的非球形飞尘气溶胶粒子结果进行了对比分析;由理论与实验方法得到的散射相函数,采用离散坐标法计算了两者的双向反射函数(BRDF),并对此结果进行了分析研究。结果表明:实验测量的非球形飞尘气溶胶粒子群的散射矩阵和基于球形粒子假设的Mie散射理论计算结果在大多数散射角上都不相同,但是不对称因子却大致相同;球形-非球形粒子群的BRDF随反射角的变化趋势基本一致,但是球形粒子群的BRDF曲线分布具有更大的波动趋势;随着光学厚度的增加,球形-非球形粒子群的BRDF曲线分布均趋于平坦,计算结果趋于一致。因此在飞尘气溶胶粒子散射特性研究中,当光学厚度较小时,用球形假设的方法会造成一定的误差,BRDF相对误差最大可以达到60%,需考虑粒子非球形特性造成的影响;而当光学厚度较大时,BRDF相对误差一般不会超过10%,采用球形假设的方法具有一定的适用性。     

随机取向团簇自然气溶胶光学特性

利用离散偶极子近似法计算分析了随机取向团簇自然气溶胶(包含灰尘和海盐)在等效半径变化范围为0.01～2 m（波长为0.55 m时对应尺度参数为0.1～23)时的光学特性。通过考察成分和形状的影响,计算结果表明:成分对团簇自然气溶胶的散射、后向散射效率因子,不对称因子,以及米散射区范围内的消光效率因子的影响均较小,其中对尺度参数为9～23时的消光效率因子和尺度参数小于2.3时的不对称因子几乎没有影响;成分对瑞利散射区范围内的消光效率因子及吸收效率因子的影响相对较大。形状对团簇自然气溶胶在尺度参数小于0.7时的消光、吸收、散射效率因子及后向散射效率因子的影响可以不计;当尺度参数大于4.6时,粒子的内在对称性和表面的突变会带来明显的影响。另外,团簇自然气溶胶在米散射区内、尺度参数较大时,散射相函数有明显的后向散射加强效应。     

不同形状的非球形粒子对偏振传输特性的影响

针对自然界的非球形粒子问题,对典型非球形粒子的偏振传输特性进行研究,采用T矩阵算法研究椭球、圆柱和切比雪夫粒子的偏振传输特性,及其与球形粒子偏振传输特性的差异。研究结果表明:对于横纵轴之比中等的椭球粒子,当散射角小于60°时,不同形状椭球粒子的偏振度(DOP)差异较小,可用Mie散射方法进行粒子偏振特性的近似计算;当散射角大于60°时,DOP随横纵轴之比的变化较大,且球形与椭球粒子的DOP差异随着横纵轴之比的增加而增大;对于直径与高度之比中等的圆柱体粒子,DOP的变化相比于椭球粒子更加平稳,但后向散射与侧向散射区域仍不能采用Mie散射进行近似计算;形状比例极端的椭球粒子和圆柱体粒子的偏振曲线均类似于钟形,且在散射角约为90°时DOP达到最大值;切比雪夫粒子的形变参数和级次都对粒子前向散射偏振特性的影响较小,但对后向散射偏振特性的影响较大,且灵敏度随级次的增加而减小。本研究结果可为非球形粒子偏振传输特性的研究及球形粒子近似提供理论指导。     

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。     

掺杂对随机取向团簇粒子辐射特性的影响

利用Bruggeman有效介质理论得到了占有不同体积份额杂质的团簇粒子的等效复折射率.采用离散偶极子近似方法对包含有不同化学成分的随机取向团簇粒子的散射相函数、消光、吸收、散射效率因子、单次散射反照率以及不对称因子等辐射特性参量进行了数值计算,深入探讨了掺杂量对随机取向团簇粒子辐射特性的影响.研究表明,掺杂对随机取向团簇粒子的辐射特性产生显著的影响,并且此影响随着粒子尺度参量的变化而变化.这一工作对研究多种化学成分组成的混合气溶胶的辐射及气候效应具有重要科学价值.     

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。     

随机取向气溶胶凝聚粒子光学特性研究北大核心CSCD

利用Cluster-cluster aggregation(CCA)模型,模拟了由64个球形原始微粒凝聚而成的四种随机取向气溶胶凝聚粒子.结合离散偶极子近似方法,分别得到了不同入射角和不同尺寸参数情况下气溶胶凝聚粒子的吸收、散射、消光效率因子和不对称因子的数值结果,并比较分析了四种形状气溶胶凝聚粒子吸收、散射、消光效率因子和不对称因子的差异.结果显示:对于相同数目原始微粒的气溶胶凝聚粒子,其光学特性明显依赖于入射光的入射角度和气溶胶凝聚粒子的形状;对于不同尺寸参数的气溶胶凝聚粒子,当入射光波长给定时,吸收、散射和消光效率因子最初随尺寸参数增大而快速增大,随后又随尺寸参数增大缓慢变小,但在尺寸参数变化过程中存在一个极大值;不对称因子则随尺寸参数的增大一直呈增大趋势,且随尺寸参数的增大趋近于1.     

随机取向气溶胶凝聚粒子光学特性研究

利用Cluster-cluster aggregation (CCA)模型,模拟了由64个球形原始微粒凝聚而成的四种随机取向气溶胶凝聚粒子。结合离散偶极子近似方法,分别得到了不同入射角和不同尺寸参数情况下气溶胶凝聚粒子的吸收、散射、消光效率因子和不对称因子的数值结果,并比较分析了四种形状气溶胶凝聚粒子吸收、散射、消光效率因子和不对称因子的差异。结果显示：对于相同数目原始微粒的气溶胶凝聚粒子,其光学特性明显依赖于入射光的入射角度和气溶胶凝聚粒子的形状;对于不同尺寸参数的气溶胶凝聚粒子,当入射光波长给定时,吸收、散射和消光效率因子最初随尺寸参数增大而快速增大,随后又随尺寸参数增大缓慢变小,但在尺寸参数变化过程中存在一个极大值;不对称因子则随尺寸参数的增大一直呈增大趋势,且随尺寸参数的增大趋近于1。     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.     

A stereo matching algorithm using multi-peak candidate matches and geometric constraints

Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate.