Characterization of optically soft spheroidal particles by multiangle light-scattering data by use of the neural-networks method

A method for evaluating the size of optically soft spheroidal particles by use of the angular structure of scattered light is proposed. It is based on the use of multilevel neural networks with a linear activation function. The retrieval errors of radius R of the equivolume sphere and aspect ratio e are investigated. The ranges of the size of R, e, and the refractive index are 0.3-1.51 microns, 0.2-1, and 1.01-1.02, respectively. The retrieval errors of the equivolume radius and aspect ratio are 0.004 micron and 0.02, respectively, for a three-level neural network (at a precisely measured angular distribution of scattered light). The retrieval errors of R and e for a one-level neural network are 2-5 times greater. The errors for a multilevel neural network increase faster than those for a single-level network.     

Particle sizing by multiangle light-scattering data using the high-order neural networks

The problem of retrieval of size and refractive index of a spherical particle by angular dependence of scattered light in scanning flow cytometry is considered. For its solution, the high-order neural networks are used. We restricted the range of angles available for measurement from 10° to 60°. The retrieval errors of characteristics of nonabsorbing particles were investigated at the ranges of the radius and relative refractive index 0.6–10.6 μm, and 1.02–1.38, respectively.     

Characterization of spherical particles using high-order neural networks and scanning flow cytometry

We retrieve the radius R, real n and imaginary k parts of the refractive index of homogeneous spherical particles using angular distribution of the light-scattering intensity. To solve the inverse light-scattering problem we use a high-order neural-network technique. The effect of network parameters on optimization is examined. The technique is evaluated for noise-corrupted input data at 0.6 μm<R<10.6 μm, 1.02<n<1.38, and 0<k<0.03. The errors of retrieval for nonabsorbing particles do not exceed 0.05 μm for radius and 0.015 for refractive index. The experimental verification is fulfilled by experimental data retrieved by means of a scanning flow cytometer. The light-scattering profiles of polystyrene beads and spherized red blood cells are processed with the high-order neural networks and a non-linear regression at Mie theory. The parameters retrieved by the high-order neural networks correlate well with the parameters retrieved by the least-square method.     

Refined calibrations of the turbidity spectrum for ill-defined disperse systems

A corridor type of calibration curves of the turbidity-spectrum method is proposed for ill-defined disperse systems. It is found that the cubic-mean radius of particles strongly depends on factors to which optical instruments have a low sensitivity. The concept of an effective cubic-mean radius is introduced and an algorithm for constructing corridor calibration curves for this radius is given on the basis of the method of realistic (instrument-dependent) differentiation, which was proposed earlier. An example of a calibration curve for a relative refractive index of 1.12 is presented.     

A Compton scattering image reconstruction algorithm based on total variation minimization

Compton scattering imaging is a novel radiation imaging method using scattered photons.Its main characteristics are detectors that do not have to be on the opposite side of the source,so avoiding the rotation process.The reconstruction problem of Compton scattering imaging is the inverse problem to solve electron densities from nonlinear equations,which is ill-posed.This means the solution exhibits instability and sensitivity to noise or erroneous measurements.Using the theory for reconstruction of sparse images,a reconstruction algorithm based on total variation minimization is proposed.The reconstruction problem is described as an optimization problem with nonlinear data-consistency constraint.The simulated results show that the proposed algorithm could reduce reconstruction error and improve image quality,especially when there are not enough measurements.     

The effect of the size of particles on optical and electrooptical properties of colloids

We have considered optical and electrooptical properties of disperse systems that contain particles with different optical characteristics, sizes, and shapes. Our investigations of the refractive index of a series of disperse systems have shown that, if the particle size does not exceed a few tens of nanometers, the refractive index does not depend on the particle concentration and is equal to the refractive index of a molecular medium that surrounds particles. We have shown that, in an external electric field, systems with these particles almost do not possess birefringence but possess dichroism. Our investigations of systems with a low concentration of particles allowed us to find that the intensity of light transmitted through a Kerr cell that is filled with colloidal particles with a size comparable with the wavelength and that is placed between crossed polarizers varies proportionally to the squared dichroism induced in the colloid by the external field. Linearly polarized light transmitted through this cell in the electric field remains to be linearly polarized, but its plane of polarization rotates by an angle the tangent of which is proportional to the dichroism of the colloid. We propose a method for determining the contributions from birefringence and dichroism to the observed electrooptical effects.     

非球形椭球粒子参数变化对光偏振特性的影响

针对自然界中多数沙尘、烟煤粒子的非球形问题, 在球形粒子偏振特性的基础上, 进一步研究非球形椭球粒子的折射率、有效半径、粒子形状等参数变化对光偏振特性的影响, 采用基于T矩阵的非球形粒子仿真方法, 模拟非偏振光经椭球粒子传输后光的偏振特性及其与球形粒子间的差异, 并以实际沙尘、海洋、烟煤三种气溶胶粒子为例说明结果的正确性. 结果表明: 当折射率实部越小, 虚部越大时, 球形粒子与非球形粒子的偏振差异越不明显; 当粒子有效半径增加时, 球形粒子偏振度的变化比非球形粒子更为明显, 且最大值分别出现在散射角为150°和120°的位置; 当粒子形状不同时, 不同形状椭球及球形粒子的差异在散射角小于60° 时并不明显, 且当椭球粒子纵横比互为倒数时, 两种粒子的偏振特性近似相同. 通过以上分析可知, 在光传输过程中, 椭球粒子多数情况下无法被近似为球形粒子进行计算.     

Numerical study of the extinction matrix for a plate crystal

Energy and polarization characteristics of optical radiation passed through a semitransparent plate crystal with a preset orientation in space are studied numerically within the framework of the method of physical optics. Results of calculations of the extinction matrix elements versus particle size, refractive index, crystal orientation, and incident radiation wavelength (from 0.5 to 15 μm) are presented. It is demonstrated that K₁₁, K₁₂, and K₃₄ are most informative among the elements of the extinction matrix. It is established that the first of them is most sensitive to changes in the microphysical and orientational parameters of the particle when the angle of radiation incidence on the plate changes from 0 to 20°, and the nondiagonal elements are most sensitive when the angle of radiation incidence is greater than 40°. The characteristics of the total field scattered near the forward direction are determined. It is established that their dependence on the physical parameters of the crystal is most strong at scattering angles smaller than or equal to 4° and wavelengths from the IR range (in particular, from the atmospheric transparency window).     

Method for retrieving the refractive index of ordered particles from data on the photonic band gap

A method for retrieving the refractive index of spherical particles arranged into ordered structures is proposed. It is based on the solution of the inverse problem using data on the photonic band gap. The solution has been obtained within the quasi-crystalline approximation of the multiple wave scattering theory and the transfer-matrix method. Quantitative results are presented for systems of silicon oxide particles. The effective refractive indices of synthetic opal particles have been found from the available experimental data on the spectral position of the photonic band gap. The described technique is applicable for retrieving not only the refractive index of particles but also other characteristics of ordered particulate structures from the coherent transmittance spectra.     

Three-dimensional optical measurement of instantaneous pressure

Local perturbations in material density induced in a material by a compressional wave give rise to local perturbations in refractive index. Accurate, high-resolution, three-dimensional, optical measurements of an instantaneous refractive index perturbation in a homogeneous, optically transparent medium may be obtained from measurements of scattered optical intensity alone. The method of generalized projections allows incorporation of optical intensity measurements into an iterative algorithm for computing the phase of the interrogating optical pulse as the solution of a fixed point equation. The complex optical field amplitude, computed in this manner, is unique up to a constant unit magnitude complex coefficient. The three-dimensional refractive index distribution may be computed via the Fourier slice reconstruction algorithm from the optical phase data under the assumption of weak optical scattering. The refractive index perturbation is related to local instantaneous pressure under a linear, small-displacement model for the mechanical wave. A numerical simulation of the measurement experiment, phase recovery, and reconstruction process for a plane piston ultrasound transducer with a semicircular aperture and center frequency of 1.5 MHz is described and corresponds very well with experiment. Experimental data obtained using an 810-nm laser source are used to reconstruct the three-dimensional pressure field from two elements of a 2.5-MHz linear array. Comparison with a measurement obtained via a 500-microm needle hydrophone shows excellent agreement.     

Design of a coated thinly clad chalcogenide long-period fiber grating refractive index sensor based on dual-peak resonance near the phase matching turning point

A novel method for designing chalcogenide long-period fiber grating (LPFG) sensors based on the dual-peak resonance effect of the LPFG near the phase matching turning point (PMTP) is presented. Refractive index sensing in a high-refractive-index chalcogenide fiber is achieved with a coated thinly clad film. The dual-peak resonant characteristics near the PMTP and the refractive index sensing properties of the LPFG are analyzed first by the phase-matching condition of the LPFG. The effects of film parameters and cladding radius on the sensitivity of refractive index sensing are further discussed. The sensor is optimized by selecting the appropriate film parameters and cladding radius. Simulation results show that the ambient refractive index sensitivity of a dual-peak coated thinly clad chalcogenide LPFG at the PMTP can be 2400 nm/RIU, which is significantly higher than that of non-optimized gratings. It has great application potential in the field of chemical sensing and biosensors.     

高折射玻璃微珠粒径与折射率关系的研究

利用激光照射高折射率玻璃微珠下形成的二次彩虹现象,以艾里的虹理论为基础对玻璃微珠折射率进行了测量。推导了玻璃微珠尺寸对折射率影响的计算公式,表明半径差异在10μm时,折射率的测量误差为10^-3数量级。此外,通过软件模拟计算玻璃微珠的二次彩虹现象,并对微珠的折射率进行了测量,验证了二次彩虹方法的正确性,同时也表明玻璃微...     

光学与粒径耦合多分散性的动态光散射研究

研究了满足Rayleigh-Gans-Debye(RGD)近似条件的球形稀溶液的光学和粒径多分散性耦合的动态光散射技术检测问题.在分析中采用了球壳L和球核R-L都连续变化且壳层变化满足L=αR (其中α<1和R是壳球半径)的壳-核硬球模型.得出了在溶剂折射率n_m和壳层折射率n_s匹配时,即n_m=n_s,平均散射强度I(q)和等效扩散系数D_e(q)与散射矢q间的关系.给出了用以检测窄分散系统小多分散性 关键词：     

高斯波束致微粒旋转的理论研究

基于偏振光波是左旋光子与右旋光子组成的, 从广义米理论出发, 得出了偏振高斯波束对球形粒子的辐射俘获力和力矩的表示式. 分析了微粒在圆偏振高斯波束照射时产生两种不同旋转的原因, 并结合光子的量子特性进行了解释. 对圆偏振高斯波束中粒子的两种力矩进行了数值模拟, 讨论了粒子半径、折射率、吸收系数和束腰半径对力矩及光致旋转的影响. 关键词： 光致旋转 力矩 高斯波束 光子     

Exploring PDA Configurations

This paper reviews the principle of the phase-Doppler particle sizer by means of examples of the effects of varying the various experimental parameters. The examples are computed by means of a comprehensive numerical model of a complete phase-Doppler system including many practical aspects such as aperture size, polarization filters and detector properties. First the phase-Doppler principle is explained as a logical development of an interferometric measurement of the phase of the light scattered from a particle. Then the standard phase-Doppler analyzer (PDA) is decribed followed by some newer or less known variations of the principle intended to measure, e.g., in the backscatter direction, to size very small particles or to determine the refractive index of a particle. Finally, the trajectory problem in PDA measurements is briefly discussed.     

On the scintillations of radiation from an extended source in a randomly inhomogeneous medium

Using the method of refractive scattering of radio waves (RSRW), we solve the problem of space correlation of scintillations of radiation from an extended source in a randomly inhomogeneous medium. General expressions are obtained for the index and radius of the space correlation of fluctuations of intensity of radiation from a source with finite angular dimensions as it propagates though a multilayered medium with refractive index fluctuations. The RSRW method is similar to the diffraction calculation of space correlation of scintillations of an extended source in a thick layer with inhomogeneities. We note that under certain conditions an increase in the number of inhomogeneous layers on the radio wave propagation path leads to a pronounced decrease in the scintillation index and an increase in the space correlation of fluctuations of intensity of received radiation from an extended source. The results obtained have a simple geometric-optical interpretation. We indicate a specific feature in determining the angular dimensions of extended radio sources using the known method of scintillations. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 5, pp. 586–593, May, 1997.     

Inverse radiation problem of temperature distribution in one-dimensional isotropically scattering participating slab with variable refractive index

In this paper, an inverse analysis is performed for estimation of source term distribution from the measured exit radiation intensities at the boundary surfaces in a one-dimensional absorbing, emitting and isotropically scattering medium between two parallel plates with variable refractive index. The variation of refractive index is assumed to be linear. The radiative transfer equation is solved by the constant quadrature discrete ordinate method. The inverse problem is formulated as an optimization problem for minimizing an objective function which is expressed as the sum of square deviations between measured and estimated exit radiation intensities at boundary surfaces. The conjugate gradient method is used to solve the inverse problem through an iterative procedure. The effects of various variables on source estimation are investigated such as type of source function, errors in the measured data and system parameters, gradient of refractive index across the medium, optical thickness, single scattering albedo and boundary emissivities. The results show that in the case of noisy input data, variation of system parameters may affect the inverse solution, especially at high error values in the measured data. The error in measured data plays more important role than the error in radiative system parameters except the refractive index distribution; however the accuracy of source estimation is very sensitive toward error in refractive index distribution. Therefore, refractive index distribution and measured exit intensities should be measured accurately with a limited error bound, in order to have an accurate estimation of source term in a graded index medium.     

Analysis of ion energy impact on the refractive index of silicon nitride films by use of neural network model

Physical ion bombardment plays a crucial role in determining refractory properties of silicon nitride films. The duty ratio is also a critical parameter that controls the amount of radio frequency power delivered to a plasma. In this study, impacts of duty ratio-induced ion energy on the refractive index are investigated. Silicon nitride films are deposited using a pulsed-plasma enhanced chemical vapor deposition. Ion energy variables and their relationship with the refractive index are studied. We report a decrease of the refractive index with decreasing duty ratio as well as a strong relationship of the refractive index with the ratio of high (or low) ion energy to high ion energy flux. A neural network model is developed to predict the effect of ion energy parameters.     

一种内混合气溶胶粒子模型光散射的等效性

以包含灰尘、黑碳和水三种成分的单分散内混合初次气溶胶为例,利用消光、吸收、散射效率因子和不对称因子,探讨了以等效折射率描述具有不同成分的内混合气溶胶粒子系统的适用性。结果表明,在尺度参数为0.1～25时不同半径比下,消光、吸收和散射效率因子的等效性较好,相对误差分别在3%、3%和4%以内;不对称因子的等效性相对稍差,相对误差在13%以内。当半径比a/b小于1/5,即内混合体中所含灰尘和黑碳较少时,等效折射率实部和虚部值基本可以确定,而不必考虑尺度参数的影响。用除散射相函数之外的其他光学量来等效时,较为容易找到等效的气溶胶粒子。     

Aerosol light absorption and its measurement: A review

Light absorption by aerosols contributes to solar radiative forcing through absorption of solar radiation and heating of the absorbing aerosol layer. Besides the direct radiative effect, the heating can evaporate clouds and change the atmospheric dynamics. Aerosol light absorption in the atmosphere is dominated by black carbon (BC) with additional, significant contributions from the still poorly understood brown carbon and from mineral dust. Sources of these absorbing aerosols include biomass burning and other combustion processes and dust entrainment.For particles much smaller than the wavelength of incident light, absorption is proportional to the particle volume and mass. Absorption can be calculated with Mie theory for spherical particles and with more complicated numerical methods for other particle shapes.The quantitative measurement of aerosol light absorption is still a challenge. Simple, commonly used filter measurements are prone to measurement artifacts due to particle concentration and modification of particle and filter morphology upon particle deposition, optical interaction of deposited particles and filter medium, and poor angular integration of light scattered by deposited particles. In situ methods measure particle absorption with the particles in their natural suspended state and therefore are not prone to effects related to particle deposition and concentration on filters. Photoacoustic and refractive index-based measurements rely on the heating of particles during light absorption, which, for power-modulated light sources, causes an acoustic signal and modulation of the refractive index in the air surrounding the particles that can be quantified with a microphone and an interferometer, respectively. These methods may suffer from some interference due to light-induced particle evaporation. Laser-induced incandescence also monitors particle heating upon absorption, but heats absorbing particles to much higher temperatures to quantify BC mass from the thermal radiation emitted by the heated particles. Extinction-minus-scattering techniques have limited sensitivity for measuring aerosol light absorption unless the very long absorption paths of cavity ring-down techniques are used. Systematic errors can be dominated by truncation errors in the scattering measurement for large particles or by subtraction errors for high single scattering albedo particles. Remote sensing techniques are essential for global monitoring of aerosol light absorption. While local column-integrated measurements of aerosol light absorption with sun and sky radiometers are routinely done, global satellite measurements are so far largely limited to determining a semi-quantitative UV absorption index.