均匀球扭矩德拜级数分析(英文)

基于会聚光束所产生的扭矩来实现对小粒子的操纵已在物理学、生物学等领域得到了广泛的应用。为了分离出单个散射过程对扭矩的贡献,给出扭矩物理机理的解释,本文引入德拜级数分析了高斯波束对均匀球粒子所产生的扭矩。计算表明,当德拜项p从1取到一个足够大的值后,德拜级数计算结果与广义米氏理论结果吻合。文中重点分析了单阶p散射过程对横向扭矩的贡献,结果表明:当线极化光束入射时,p=1～5散射过程都可以产生横向扭矩,但扭矩的方向不同;当圆极化光束入射时,p=-1和0对应的扭矩远大于p=1～4对应的扭矩,且p=0过程产生与其他p过程相反方向的扭矩。     

均匀球扭矩德拜级数分析

基于会聚光束所产生的扭矩来实现对小粒子的操纵已在物理学、生物学等领域得到了广泛的应用。为了分离出单个散射过程对扭矩的贡献,给出扭矩物理机理的解释,本文引入德拜级数分析了高斯波束对均匀球粒子所产生的扭矩。计算表明,当德拜项P从1取到一个足够大的值后,德拜级数计算结果与广义米氏理论结果吻合。文中重点分析了单阶P散射过程对横向扭矩的贡献,结果表明：当线极化光束入射时,P=1～5散射过程都可以产生横向扭矩,但扭矩的方向不同;当圆极化光束入射时,P=一1和0对应的扭矩远大于P=1～4对应的扭矩,且P=0过程产生与其他P过程相反方向的扭矩。     

水中气泡上的体散射函数的模拟与计算

基于几何光学的基本原理,推导出一种可以计算水中大尺度气泡上光散射角度与强度的关系式。推导中避免引入衰减因子G,较Davis模型更为简单。该模型可应用于光在水中单个气泡上散射的数值计算。最后,模拟计算了平行光束入射水中气泡的体散射函数曲线,发现水中气泡的前向散射远大于后向散射;当气泡半径在远大于光波波长的前提下变化时,气泡上散射光强分布规律与气泡半径无关;而介质相对折射率的增大会削弱前向散射而增强后向散射光强。     

在轴高斯波束入射无限长多层圆柱散射的德拜级数解

不均匀柱形粒子的光散射特性研究对复杂结构粒子参量的反演具有重要意义。基于德拜理论,对在轴高斯波束垂直入射无限长多层圆柱的散射特性进行了讨论。获得了散射系数的德拜级数展开式;并利用该公式分别计算了均匀和双层圆柱的总散射强度角分布,德拜级数单阶散射强度角分布;总散射强度结果与广义米氏理论(GLMT)进行了比较,两者吻合很好。分析表明圆柱散射强度不同散射角区间的值来自德拜级数不同阶的散射强度贡献;双层圆柱各层半径和折射率的值对德拜级数二阶散射强度角分布中峰值的出现起决定作用。当双层圆柱的外层较薄时,在120°~150°之间会出现两个明显峰值,即出现双重一阶彩虹峰值;反之,当外层厚度大于内层时,只有一个峰值存在。     

有黏条件气泡声散射特性和衰减谱数值研究*

通过研究有黏条件下的气泡散射模型,数值分析水中单气泡声散射特性,进一步结合Beer-Lambert定律将其扩展到多气泡体系的声衰减预测。数值结果表明,随着谐波阶数递增,散射强度分布数值结果趋于稳定且前向散射增强。同时发现,无因次尺寸参量ka=0.1为过渡区与纯散射区的分界线,且在共振区间具有明显的吸收效应。对多气泡体系的声衰减预测也表明,ka 0.1时,该文气泡散射模型声衰减计算与经典ECAH模型结果吻合,在低浓度条件下声衰减谱随着剪切黏度的增加呈增宽趋势,且与体积浓度成正比例递增。模型预测的声衰减随粒径、声波频率、体积浓度分布数值特征能够为颗粒两相体系粒径及浓度表征提供理论依据。     

激光脉冲宽度对远距离尾流气泡后向检测的影响

为了分析激光脉冲宽度对远距离尾流气泡后向检测的影响,基于Fournier Forand体积散射函数,通过Monte Carlo方法建立了水中激光脉冲后向散射信号时域特征的分析模型.利用该模型研究了初始激光脉冲宽度不同时,水中远距离舰船尾流气泡的激光脉冲后向散射信号变化情况.结果表明:随着初始激光脉冲宽度的增加,后向散射信号中水体散射信号与尾流气泡回波信号的轮廓变得模糊|当脉冲宽度增大到一定程度时,无法从后向散射信号中辨别出回波信号|并且,随着尾流区气泡散射强度的减小以及气泡区与检测器之间距离的减短,这种变化趋势变得更加明显.基于仿真结果,提出一种基于逆卷积运算的尾流气泡回波信号提取方法.     

光在水中吸附膜层气泡上的散射特性

光在水中大尺度气泡上散射特性的研究多是基于Davis模型.该模型没有考虑到吸附膜层对光在气泡上散射的影响,而海水中的大多数气泡都有膜层附着,这些膜层会影响到气泡的光散射特性.本文从几何光学的角度出发,建立了吸附膜层气泡的体积散射函数简化公式.在此理论基础上,模拟计算了尺度远大于入射光波长的大气泡散射光强分布曲线,得出光照射下气泡上散射光强的远场特性,讨论了影响气泡散射光强分布的主要因素.并与无膜气泡光散射分布曲线比较,讨论了油膜膜厚、折射率等参量对气泡的光散射特性影响.得出结论:吸附膜层气泡的光强分布曲线与无膜气泡相似,但吸附膜层会削弱前向散射光,增强后向散射光.     

微粗糙面上方球形粒子的光散射及其散射截面的计算

基于互易定理研究了光波入射时微粗糙面与其上方球形粒子复合模型的光散射。根据粗糙表面电流积分方程并利用表面微扰展开，得到了微粗糙面表面极化电流的迭代解，给出了耦合电场的计算方法。结合散射耦合场散射矩阵和已有的微粗糙面及球形粒子的散射矩阵，给出了复合模型散射截面的计算公式，数值计算了复合模型的后向散射截面并进行了详细讨论。     

Mie光散射理论的数值计算方法

Mie散射级数的计算速度和精度对颗粒测量结果有着重要的影响。针对不同颗粒直径和相对折射率，一般采用前向递推，后向递推，连分式法等计算Mie散射级数。在这3种方法的基础上提出一种改进算法，即首先通过连分式法计算Mie散射级数的初始值，然后后向递推其余各值。该算法在Matlab中实现时，数据以数组的数据类型存储和调用，程序采用递归算法。通过比较计算结果发现，该算法耗时短且结果不易溢出，具有快速、稳定、不受颗粒直径和折射率范围影响等优点。     

舰船尾流气泡后向光学检测方法研究

为探索舰船尾流后向光学检测方法,研究了尾流气泡对水中激光脉冲后向散射特性的影响。首先基于Fournier Forand 体积散射函数,利用蒙特卡罗(Monte-Carlo)方法理论分析了近距离尾流气泡对激光脉冲后向散射特性的影响。然后,采用蓝绿激光脉冲作为光源,实验研究了模拟尾流气泡对激光脉冲后向散射信号的影响。研究表明,尾流气泡的存在会使得激光脉冲后向散射信号前沿位置在时域左移,后沿位置在时域右移,信号时域宽度增加,能量增强,峰值增大且位置在时域左移。最后根据研究结果提出了一种基于激光脉冲后向散射信号特征变化的舰船尾流气泡后向检测方法。     

Scattering by large bubbles: Comparisons between geometrical-optics theory and Debye series

The scattering patterns and optical properties of large spherical bubbles in water are calculated by both Geometrical-optics theory and Debye-series expansion of the Mie amplitudes. In the Geometrical-optics calculations, the wave-front spreading factor and phase information are all taken into consideration. A detailed comparison between the two methods is presented. It is found that scattering patterns calculated from the Geometrical-optics approach agree reasonably with those obtained by Debye series when the size parameter is larger than approximately 400. In the case of scattering properties, the Geometrical-optics method can produce reliable results with the Debye expansion for size parameters larger than approximately 50. The Geometrical-optics results without the phase interferences are also reliable, but it cannot display the oscillations and the ripple structure as a function of size parameter.     

Stability in Debye series calculation for light scattering by absorbing particles and bubbles

The Debye-series decomposition is of importance for understanding of light scattering features and for the validity of the geometrical optics approximation to light scattering. The numerical stability and accuracy for calculating light scattering with Debye series is studied and an improved algorithm is proposed in this work. The ratios of the Riccati-Bessel functions and the logarithmic derivatives of the Riccati-Bessel functions are employed and calculated with proper recurrences. Exemplifying results are provided to show the improvement of the algorithm.     

Influence of population and radius of cavity bubbles on size of sodium chloride crystals in ultrasound ablation

Crystal size distribution as a function of power in ultrasound ablation is simulated by using a theoretical method based on population and radius of bubbles. In this method, population and radius of bubbles are related to ultrasound power and Debye temperature of crystals. The best power for production of crystals with uniform size is obtained from the theory. In addition, it is shown that the population of bubbles effects the radius of the productions and the radius of bubbles influences the population of products. Results from the theory are supported by experimental results.     

Influence of wake bubbles on optical impulse scattering echo

The model of the optical impulse scattering echo based on Mie theory and backscattering properties of bubble populations is presented. The experimental results of optical impulse scattering echo for a ship in the ocean is in agreement with the simulated experiment. The wake bubbles significantly influence the laser scattering echo process in the ocean. When the testing system is outside the wake, the distinct scattering echoes of interface between wake bubbles and water are received. When the testing system is inside the wake, the intensity of the echo attenuates with the increased scattering of wake bubbles. These phenomena of laser echoes in different periods are analyzed.     

Analysis and comparison of n-AlxGa1−xAs/GaAs QWIPs with different device structures and optical coupling

This paper discusses optical coupling for n-GaAs/AlGaAs multiple quantum well infrared photodetectors (MQWIPs). The optical responsivity has been compared with different grating structures fabricated by reactive ion etching (RIE), device form, and incidence mode. The optical coupling efficiencies are further analyzed by the modal expansion model (MEM), including optical field distributions in different size photosensitive element and interrelated influences with scattering matrix method based on plane-wave expansion (PWE). Some extra coupling parameters have been obtained in designing and optimizing QWIPs FPA.     

基于多重散射强度和偏振特征的舰船尾流气泡激光探测方法

研究多重散射效应对舰船尾流气泡群光散射强度和偏振特征的影响是舰船光尾流探测以及新型光自导鱼雷研究的基础. 基于矢量Monte Carlo方法建立了舰船尾流气泡群激光后向探测仿真模型, 重点研究了尾流气泡群的多重散射机理,分析了多重散射效应、尾流气泡群密度对回波信号强度和偏振特征的影响规律. 基于粒子碰撞重要性抽样的基本思想, 在传统能量接收方法的基础上, 提出了回波光子偏振贡献接收方法和回波信号偏振信息统计方法, 解决了小视场系统光子返回概率低无法形成回波能量的难题. 构建了模拟尾流气泡群激光散射强度和偏振探测实验平台, 从实验的角度验证了模拟结果的准确性. 实验和模拟结果的一致性表明, 利用回波强度、偏振信息可表征气泡群距离、密度信息, 从而可对舰船尾流特别是低密度尾流进行高精度的探测和辨识. 关键词： Monte Carlo 偏振 多重散射 气泡     

基于光线追迹法的球形大粒子的多次散射计算

基于光线追迹法模拟了球形大粒子的多次散射过程,利用菲涅耳公式建立了散射矩阵的理论表达式,并利用Matlab对计算过程进行编程。以水滴为例进行了定量计算,获得了散射功率随散射次数和散射角的分布。相关结论可用于光学大气传输的定量计算。     

矩量法研究平面波导点缺陷引起的散射损耗

对平面波导工艺过程里出现的点缺陷,如气泡、灰尘颗粒等对平面波导内光场造成的散射提供了一种简单而又实用的计算方法。计算基于格林函数方法,并利用矩量法求解积分方程,采用分块矩阵优化算法,使得算法的计算时间直接与点缺陷大小相关,提高了效率。证明了一定大小的点缺陷在特定的波长处会产生很大的散射损耗,证明点缺陷的散射损耗依赖于缺陷大小和光学性质而与其在波导中的位置无直接关系。以二氧化硅平面波导为例,分析了对中心波长1．55μm的入射光场,分别存在气泡和灰尘颗粒两种点缺陷时,散射损耗随点缺陷大小的关系特性,指出工艺过程特别应该避免某些孔径的点缺陷。     

Study of dispersion and absorption of an ensemble of spherical particles inside an optical cavity and new possibilities of predicting the optical characteristics of biological media by intracavity laser spectroscopy

Optical characteristics, namely, dispersion and absorption spectra of an ensemble of spherical particles randomly oriented inside an optical cavity are investigated. The study is based on the self-consistent matching of new data from the inhomogeneous optical cavity with data from the scattering of an ensemble of spherical particles of different size, randomly oriented in free space. As a result, a new model, which self-consistently accounts for multiple scattering in the optical cavity, has been developed to predict absorption and dispersion of ensembles of spherical particles. This model is supposed to enhance potentiality of the intracavity method for plotting wavelength dependences of optical characteristics of media. A specific calculation of dispersion and absorption dependences on the wavelength shows that this method can be used for investigation of biological media consisting of spherical particles, in particular, erythrocyte suspension.