Interferometric technique for measurement of droplet diameter

The paper considers the optical contact-free method of droplet diameter sizing in the flow cross-section utilizing light interference on a droplet. Distribution of light scattered by a particle was analyzed for different configurations of the measurement system using the Mie theory and approximation of geometrical optics. Basic measurement errors and dynamic range were determined. Possibility of measurements with camera mounting at the angle of 90° to the plane of a laser sheet is shown; this simplifies setup calibration and evens characteristics over the image field. The procedure of measurement system calibration and a set of algorithms for data processing are suggested. The suggested approaches were applied for measurement of characteristics of the gas-droplet jet.     

Apparent and real roughness

Some works have studied the light scattering from a rough surface immersed in a liquid, where the light scattered from the immersed rough surface was assumed to be equivalent to that scattered from a fictitious rough surface with a different texture. This work deals with this kind of problems analyzing the light scattered by a reflecting strong scatterer and the light scattered by a rough surface immersed in a transparent liquid. The general Kirchhoff solution for scattering from a rough surface has been used.It is shown that under certain conditions, the mean scattered intensity (MSI) from a surface immersed in a liquid can be quasi-indistinguishable from that scattered from a non-immersed surface with an “equivalent texture”. An expression relating the equivalent texture and the immersed surface texture was obtained.The results of this work allow to evaluate the characteristics of any surface immersed in a liquid with a known refractive index.     

Optical characteristics of LGP depending on the scattering pattern orientation for flat-type LED lighting

In flat-type light-emitting-diode (LED) lighting systems, a planar light is formed using a luminance source positioned on the side of the system and light guide panel (LGP) or reflecting plates. Thus, such systems are favorable for their thinness, which allows a relatively small number of LEDs to be used. However, the application of a high-power LED light to a large-area lighting system yields Lambertian luminaires; therefore, a point or a discomfort glare is produced, which generally causes degradation of the luminance efficiency and uniformity. In this study, we solved the problems of luminance non-uniformity and inefficiency by adjusting the orientation of an applied LGP scattered pattern and removing the remaining glare. Through computer simulation, optical characteristics that increase the efficiency even in the case of low-output LEDs were found. Specifically, a scattered pattern vertically oriented relative to the direction of the incident light improves the luminance uniformity at the side of the system, while a scattered pattern oriented parallel to the direction of the incident light plays the role of a waveguide. We implemented a flat-type LED lighting system by fabricating a large-area LGP based on the computer-simulation results and using an extremely sensitive laser. The optical characteristics observed using the laser-processed LGP were identical to those obtained in the computer simulation. Therefore, for large-area flat-type LED lighting systems, we confirmed that adjusting the orientation of the LGP scattered pattern can increase the luminance efficiency and uniformity.     

Two-particle characterization by pulse induced and time resolved Mie scattering

With this numerical investigation we demonstrate the determining of particle size and particle distance for a two-particle system by time resolved Mie scattering. The optical interaction of the fs-laser pulse with the particle configuration produces a sequence of scattered light signals on the femtosecond time scale. The temporal differences between these signals represent typical dimensions of the particle system. The different ray tracks of the specific scattering orders, which are the reason of the temporal behaviour, have been verified by models of geometric optics. We have simulated the Mie scattered light by an algorithm for multi-particle scattering. For all examples the detector was positioned in the back scattering region at a scattering angle of θ=150°.     

Optical characterization of metallic aerosols

Airborne metallic particulates from industry and urban sources are highly conducting aerosols. The characterization of these pollutant particles is important for environment monitoring and protection. Because these metallic particulates are highly reflective, their effect on local weather or regional radiation budget may also need to be studied. In this work, light scattering characteristics of these metallic aerosols are studied using exact solutions on perfectly conducting spherical and cylindrical particles. It is found that for perfectly conducting spheres and cylinders, when scattering angle is larger than 90° the linear polarization degree of the scattered light is very close to zero. This light scattering characteristics of perfectly conducting particles is significantly different from that of other aerosols. When these perfectly conducting particles are immersed in an absorbing medium, this light scattering characteristics does not show significant change. Therefore, measuring the linear polarization of scattered lights at backward scattering angles can detect and distinguish metallic particulates from other aerosols. This result provides a great potential of metallic aerosol detection and monitoring for environmental protection.     

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.     

Theory of Raman scattering in Europium-chalcogenides

The intensity of the spin assisted Raman scattering in the Eu-chalcogenides is calculated using the excited states which were used in the analysis of the optical absorption. Various mechanisms are examined for the Raman scattering. In these mechanisms, the cross effect of the 4f spin-orbit interaction and the exciton-phonon interaction is found to be the most important for the scattering intensity. The characteristics of the Raman scattering from this mechanism are as follows: When the frequency of the incident light is in the tail region of the absorption peak, the polarization of the scattered light is perpendicular to that of the incident light; when the light in the middle region of the absorption peak is applied, the polarization of the incident light is depolarized in the scattered light; the scattering intensity decreases when the spin fluctuation is suppressed by an application of magnetic field or by lowering temperature through the Curie temperature. These characteristics in the Raman scattering have been observed in the experiments.     

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.     

Fundamental Study on Near-Axis Scattered Light and Its Application to Optical Computed Tomography

To find a basic principle of optical computed tomography (optical CT), a fundamental study was conducted on the use of scattered light in diffuse random media. We call the scattered light that propagates along the optical axis of the incident light beam near-axis scattered light (NASL). The use of NASL for the imaging through a diffuse medium was proposed and its basic characteristics were analyzed. The existence and measurability of NASL were confirmed in the simulation and measurement. To detect NASL efficiently, a technique called the scattering angle differential technique was developed. In CT imaging with a model phantom, the feasibility and effectiveness of the proposed technique were verified. We found that this technique alone was not sufficient to obtain the cross sectional image of an animal body, therefore a technique called the contact technique was devised to overcome the problems of reflection and refraction at the air-tissue interface. Finally, a prototype system was developed which integrated all the proposed techniques. With this system, we could obtain the CT images of a living mouse, in which the blood-rich organs such as liver and kidneys were clearly recognizable.     

Angular intensity distribution of scattered light in systems of closely spaced particles

The results of experimental and computational investigations of the dependence of the angular intensity distribution of scattered light on the concentration of scatterers are discussed. It is shown that a high density of small and large scatterers in a three-dimensional system results in a deformation of the scattering indicatrix. The changes in the angular distribution of intensity of the scattered light at large concentrations are explained by the appearance of fields of multiply scattered waves at significantly lower optical thicknesses than for independent scatterers.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 99–103, March, 1976.     

基于偏振门的动态光散射颗粒测量法的研究

为了解决动态光散射纳米颗粒测量技术无法测量高浓度颗粒粒径的难题,提出了一种基于偏振门的动态光散射测量法。从动态光散射和Mie理论出发,理论分析了在高浓度溶液下多重散射效应对散射光偏振态和颗粒粒度测量结果的影响。根据散射光偏振特点,结合偏振门检测技术,改进了传统的动态光散射光学系统。实验研究了在低浓度和高浓度溶液时,不同偏振角度下的散射光强和粒度测量值,完善了散射光的偏振理论。采用90°偏振门检偏,通过各种浓度下的实验,证明了方法的可行性。该方法较之目前同类方法具有原理和结构简单,系统易于维护的特点。     

Optical testing of hard disks

A device and methodology for surface testing of hard disk blanks are presented. A beam of laser light is scanned in a spiral pattern across the disk, and surface defects are diagnosed from the modulation of the scattered light. Since acceptable polish marks also scattered significant levels of light, it was necessary to make use of the directional characteristics of the scattered light in the disk test device.     

The effect of double scattering on critical fluid Rayleigh linewidth measurements

We apply recent work on the intensity correlation function of light double scattered from a system of brownian diffusing balls to the case of a fluid near the critical point. We evaluate the relative intensities and intensity correlation times of the polarized and depolarized components of the double scattered light as a function of k₀ξ. We compare these correlation times to those found for single scattering and find that the more intense polarized component of the double scattered light has a correlation time nearly equal to the singly scattered light in the critical region where $\text{k}{}_0\text{ξ ? 8}$.     

国家自然科学基金(40776059)资助

为了克服水下探测中后向散射光背景噪音的影响,提出了非均匀光场水下探测方法,推导得出非均匀光场的照度分布函数与接收口径、目标与接收器的距离以及海水的体积衰减系数几个因素有关.通过搭建集束光水下图像系统,对其产生的非均匀光场的分布特性和水下探测特性进行了水池实验.观测结果为,在0.6倍能见度下,可分辨1 mm细节,在1倍能见度时,可分辨目标轮廓,在1.5倍能见度时,可探测到目标.结果证明,该系统具有宽视角、全景深、图像清晰度高等特点.     

Multiple light scattering from a moving layer of Brownian particles: comparison with a rigid phase screen

Abstract

The temporal fluctuations in the intensity of light scattered by a moving layer of emulsions and suspensions containing Brownian particles are investigated experimentally, and a comparison is made with light scattered by a translating phase screen. The intensity fluctuations of the scattered light are detected through an imaging system, which collects the light emanating only from a limited volume in the medium. The effect of translational motion of the particle layer on the decay rate of the autocorrelation function of intensity fluctuations depends on the illuminating form of a laser beam and on the point spread function of the imaging system. The Brownian motion of the particles causes the scattered light to fluctuate more rapidly than that arising from the translating phase screen. In the multiple-scattering regime, the influence of this diffusional motion increases with an increase of the particle concentration in the layer.     

Transparent,flexible and low‐resistive precision fabric electrode for organic solar cells

We report the use of conducting precision fabrics as transparent and flexible electrode for organic semiconductor‐based thin film devices. Precision fabrics have well‐defined mesh openings, excellent flexibility and are fabricated by high‐throughput roll‐to‐roll manufacturing. Optimized fabrics reached light transmittance over 95% throughout the visible and near infrared spectra. A significant part of the transmitted light is scattered, which is particularly advantageous for solar cell applications. Surface resistivity is as low as ～3 Ohms/square, which decreases Ohmic losses when scaling up to large area devices. We demonstrate that solar cells fabricated onto these electrodes show very similar characteristics to those prepared on ITO. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Detection of scattered light pulses at femto-Joule level by using a picosecond BBO optical parametric amplifier

We report a technique for detecting weak scattered light pulses based on a 532 nm pumped picosecond β-barium-borate collinear optical parametric amplifier. The measured maximum slope gain factor of the amplifier was found to be around 10⁷, and the energy detection limit was of the order of fJ/pulse for the signal of 730 nm and the idler of 1.5 μm at a pumping intensity of 2.83 GW/cm². The linearity of the gain for this amplifier was found to be excellent for a seeding level of lower than 420 fJ per pulse. The maximum gains and the energy detection limits for the scattered light pulses from various scattering targets were found to be poorer than that from the reflective mirror, owing to the degraded beam quality and the depolarization of the scattered light. A reduction of the maximum gain for the scattered light with the increase of the angle of incidence, which causes pulse broadening and reduces the photon flux of the signal, was investigated. The feasibility of detecting weak scattered light in the infrared by using idler-to-signal frequency up-conversion was also demonstrated, in which the infrared seeder located in the idler branch of the amplifier was injected as the seeding beam and was then parametrically up-converted into the visible signal branch, with an even higher gain.     

尘埃粒子计数器中光源对传感器光通量的影响分析

在Mie散射理论基础上，由单分散射的光强表达式导出在偏振光的入射条件下一定立体角内的散射光通量的表达式，并与自然光入射作比较。计算了在相同强度不同光源入射下，尘埃粒子计数器的两种常用散射光收集系统收集的散射光通量。结果表明：采用近前向散射光收集系统得到的光通量相等；而采用直角方向散射光收集系统时两者并不相等，且在平面偏振光入射时，收集的散射光通量还跟探测器中心与入射光偏振方向夹角有关。用MATLAB编程计算，得出了在探测器中心与偏振方向的夹角成90°或270°位置时，收集的散射光通量有极值的结论，为激光尘埃计数器传感器光学设计提供了依据。     

Direct determination of gas velocity and gas temperature in an atmospheric-pressure argon-hydrogen plasma jet

Direct gas temperature and gas velocity measurements made in the exit plane of a subsonic argon-hydrogen thermal plasma jet from high-resolution lineshape analysis of laser light scattered by the plasma are reported. The lineshapes are in general a superposition of the ion feature of the Thomson-scattered light and the lineshape of Rayleigh scattered light. In the center of the jet Thomson scattering dominates while at larger radii Rayleigh scattering dominates. Because of the complexity of the lineshapes of light scattered by multicomponent plasmas, only those that are predominantly due to Thomson scattering can in practice be analyzed for gas temperature. Gas velocity can be determined from the Doppler shift of the lineshapes relative to the frequency of the incident laser if the velocity is greater than about 50 m s⁻¹. The maximum gas temperature measured was 14,500 K±5%. The maximum gas velocity measured was 1100 m s⁻¹±3%. Temperature values and the radial velocity profile are compared with those previously obtained from a subsonic all-argon plasma jet operated under similar conditions.     

Temporal characteristics of communications channels between source and receiver in inhomogeneous medium

The temporal translation properties of communications channels between a source and receiver in an inhomogeneous medium are investigated. For this, special characteristics are introduced: the average propagation time, the time variance of signal arrival, the probability of normal arrival, and the probability of division of direct and scattered signals by inhomogeneities. Spatial maps of the distributions of the characteristics are constructed for the example of a bilinear layered waveguide. Recommendations on the use of these maps for the solution of various practical problems are provided.Institute of Applied Physics, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 11, pp. 1373–1387, November, 1994.