Optical properties of pigmented coatings taking into account particle interactions

A T-matrix approach is used to obtain the orientation-averaged scattering and absorption cross sections of randomly oriented particle clusters, and the average angular distribution of the radiation scattered by them. The coefficients involved in the expansion of the phase function are obtained from this T-matrix approach, and used in a multiple scattering formalism to characterize the angular distribution of the diffuse radiation propagating through a particulate coating perpendicularly illuminated with collimated visible radiation. Asymmetry between forward and backward propagating diffuse radiation intensities is taken into account by means of this multiple scattering approach, which is based on solving the radiative transfer equation for successive scattering order contributions. A four-flux model is applied to compute the reflectance in terms of wavelength of the incident radiation and particle concentration. An application of the formalism is carried out to predict the optical properties of titanium dioxide pigmented polymer coatings, in terms of the pigment volume fraction and the degree of aggregation.     

Theoretical analysis of optical properties of dielectric coatings dependence on substrate subsurface defects

A model for refractive index of stratified dielectric substrate was put forward according to theories of inhomogeneous coatings. The substrate was divided into surface layer, subsurface layer and bulk layer along the normal direction of its surface. Both the surface layer (separated into N₁ sublayers of uniform thickness) and subsurface layer (separated into N₂ sublayers of uniform thickness), whose refractive indices have different statistical distributions, are equivalent to inhomogeneous coatings, respectively. And theoretical deduction was carried out by employing characteristic matrix method of optical coatings. An example of mathematical calculation for optical properties of dielectric coatings had been presented. The computing results indicate that substrate subsurface defects can bring about additional bulk scattering and change propagation characteristic in thin film and substrate. Therefore, reflectance, reflective phase shift and phase difference of an assembly of coatings and substrate deviate from ideal conditions. The model will provide some beneficial theory directions for improving optical properties of dielectric coatings via substrate surface modification.     

Spectral diffuse reflectance measurements of gadolinia, silica thin film systems using synchrotron radiation

Diffuse reflectance or optical scattering in thin films and multilayers can pose serious limiting factors to their desired or ultimate performances. Besides, such studies provide valuable information related to the buried microstructures and interfaces. Synchrotron radiation is the most appropriate source to record wavelength dependent polarized light scattering in thin films and multilayers. In the present experiment several gadolinia, silica thin films and multilayers were studied for their light scattering using the white light synchrotron beam. Various thin film layer geometries were selected to probe the results due to different types and combinations of interfaces. Due to phase coherent delay in certain optical non-wedged component used in the experimental setup very interesting spectral interference were noticed as the modulations in the diffuse reflectance signal. Appropriate modeling approach utilizing Gaussian function de-convolution technique is used to compute the pulse delay between the back reflected and forward propagating scattering signals that lead to such spectral interference. Alternatively inverse fast Fourier transform (IFFT) and analytical techniques were adopted to determine the group delays. The diffuse reflectance spectra were finally compared with their specular counter part and a shift both in the wavelength and phase were noticed. This may be explained on the basis of thin film roughness factors, different polarizations and incident geometries used in the measurements. However, all most all the spectral scattering signals exhibited the features resembling their specular reflection characteristic.     

薄膜非均匀性及其对增透膜性能的影响

基于非均匀膜理论提出的折射率分层模型,将非均匀膜层分为N个均匀子层,应用光学薄膜特征矩阵对其进行理论分析。应用膜系设计软件模拟ZrO2和CeO2的负非均匀性对增透膜光谱特性的影响。研究结果表明:负非均匀性使多层增透膜的反射率增大,在参考波长处的光谱特性变差,使整个反射光谱曲线朝长波方向漂移,从而导致整个膜系的光谱特性偏离理想情形。     

基于漫反射光谱的组织光学参数测量系统与方法研究

在体组织光学参数测量是生物医学光子学研究重点,不仅为人体成分无创检测、光学成像、光动力疗法等研究提供基础,并且可以快速获取人体光学参数变化,为临床诊断提供依据。研究了利用单一源探距离漫反射光谱在体测量光学参数的测量系统与反构方法。漫反射光谱测量系统由宽谱光源、高分辨光纤光谱仪及光纤探头组成,结构简单,测量方便,可准确快速测量样品漫反射光谱。在光纤探头几何形状基础上,研究了光纤收集及系统传递函数,在此基础上对反构算法进行了校正。光学参数反构算法中正向模型基于Monte Carlo以及神经网络方法,适用光学参数范围大,计算速度快;逆向算法采用主成分分析与非线性建模拟合相结合的方法,可抑制测量噪声影响。在测量系统及反构算法基础上,进行了组织仿体光学参数测量实验,结果表明,利用单一源探距离下漫反射谱,可以较为准确获取吸收系数以及约化散射系数,均方根误差分别达到4.58%以及7.92%。为保证系统测量准确性,测量波长范围应覆盖样品中所含吸收物质吸收峰范围。所研究的在体组织光学参数测量方法为人体成分无创检测及测量条件变化获取提供了基础。     

Diffuse reflectance spectra of aluminum oxide micropowders,modified powders,and nanopowders and their changes upon electron irradiation

Comparative analysis of the diffuse reflectance spectra (300–2100 nm) and of the integrated absorption factor of coatings based on micropowders, nanopowders, and micropowders modified with Al₂O₃ nanopowders has been performed. In addition, the changes in the spectra resulting from electron irradiation of the powders with energies of 30 keV at a fluence of up to 3∙16 cm^–2 have been analyzed. It has been found that the diffuse reflectance decreases in order of coatings based on micro-powders, nano-powders and modified powders, while radiation resistance increases in order of coatings based on nano-powders, modified and micropowders.     

The effect of heating on optical properties and radiation resistance of coatings based on micro- and nanosized aluminum oxide powders

Comparative analysis of the effect of heating in air (at T = 800°C for 2 h) on the diffuse reflectance spectra in the range of 360–2100 nm and on the integrated coefficient of the solar radiation absorption of coatings based on Al₂O₃ micro- and nanopowders has been carried out. Their variation under electron irradiation has been studied. It is established that the heating of powders deteriorates the optical properties and radiation resistance of coatings.     

三维漫射光谱法检测猪肉嫩度的初步研究

猪肉是光的强散射物质,嫩度是评价猪肉品质优劣的重要标准之一,提出一种基于三维漫射光谱法的猪肉嫩度检测方式。将猪肉样本更多的散射信息引入光谱分析中。利用实验室搭建的数据采集系统,通过采集距光源入射点不同距离处的样本漫反射光信号构建了64个猪肉样本的三维漫射光谱。经过小波消噪处理后,利用多维偏最小二乘法(NPLS)建立了三维漫射光谱与猪肉嫩度之间的分析模型,模型的校正决定系数R2_Cal是0.883 1,校正标准差RMSEC是3.685 0N,预测决定系数R2_Pred是0.874 7,预测标准差RMSEP是3.9756N。实验结果表明, 与常规的漫反射光谱法相比,三维漫射光谱法所建立的猪肉嫩度NPLS模型具有更高的校正精度和预测稳健性,有望为猪肉嫩度及其他品质的快速检测提供一种新的途径。     

不同含水量黑土土壤光谱反射率半经验模型构建

土壤含水量的变化情况与时空分布对热量平衡、农业墒情等具有显著的影响。利用反射率光谱信息反演土壤含水量的研究,可为实现土壤含水量速测、揭示土壤含水量时空变异规律提供科学依据。构建不同含水量黑土土壤反射率光谱半经验模型,深入探究土壤重量含水量与反射率光谱的关系。 制备了12种不同湿度的土壤样品。 采用ASD Field Spec Pro 3地物波谱仪对制备的不同湿度梯度的黑土土壤进行反射率光谱测量。 利用菲涅耳反射率建立土壤表面反射模型;在以往的研究中,Kubelka-Munk (KM)模型中的漫反射率R_∞通常被视为对于给定材料和照明波长的常数或需要反演的参数。通过研究发现,漫反射率R_∞不仅与材料和波长有关,还与土壤含水量相关。利用与土壤含水量相关的吸收系数及散射系数描述了土壤含水量与漫反射率R_∞的关系,并基于KM理论对体散射分量进行建模;进而构建不同含水量黑土土壤反射率光谱半经验模型。 根据实际测量数据选用最小二乘算法对模型参数进行反演,并通过分析反演参数简化模型。最后,将未参与建模的不同含水量梯度的数据代入模型中,验证模型的有效性。结果表明：对比不同含水量土壤反射率光谱的模拟值与实测值在400～2 400 nm波段范围内的模拟精度发现,含水量为200 g·kg-1的土壤反射率光谱的均方根误差最大,为0.008,含水量为40 g·kg-1的土壤反射率光谱的均方根误差最小,为0.000 6,不同含水量下土壤样品反射率光谱的均方根误差的均值是0.005 1。在400～2 400 nm波段范围内,不同波长下黑土土壤反射率光谱的预测均方根误差基本低于0.008,1 920 nm波长处的预测均方根误差最小,为0.002 062。采集长春地区的土壤检验模型的可靠性,配制15个不同含水量样品并对其进行反射率光谱测量。选取9个样品数据用于建模,6个样品数据用于验证。结果表明：在400～2 400 nm波段范围内,不同波长下的长春土壤反射率光谱的预测均方根误差基本低于0.015,525 nm波长处的预测均方根误差最小,为0.000 922 5。综上所述,所建立的模型具有很高的预测精度,可很好地适用于不同含水量黑土土壤反射率光谱的模拟。     

基于delta-P1近似模型的空间分辨漫反射一阶散射参量灵敏度研究

以delta-P1近似光学模型为基础, 推导了双点源近似下空间分辨漫反射一阶散射参量μ_s'灵敏度的解析式, 并进行了数值分析和比较. 研究表明, 与混合漫射近似模型和漫射近似模型相比, delta-P1 近似模型能更好地描述强散射较强吸收情况下近光源区域生物组织漫反射光子的分布, 且在有效反照率a'>0.83时, 获得最佳优化距离ρ_opt, ρ_opt 随μ_s' 的增大而减小, 且在距光源约2.7—4个输运平均自由程处μ_s'的变化对测量吸收的影响最小. 这项研究对于优化传感器几何结构以及生物组织光学参量的测量具有重要意义.     

Photothermal diffuse reflectance: a new tool for spectroscopic investigation of scattering samples

A new method named photothermal diffuse reflectance (PTDR) is presented. This method combines the diffuse reflectance spectroscopy with the photothermal technique and is particularly suited for the investigation of strongly scattering samples. This method takes advantage of the high spectral selectivity and absorption of the mid-infrared region with the larger scattering cross section and high detector sensitivity available in the near-infrared. A model describing the PTDR method is proposed and supported with experimental results. The potential of the PTDR technique is illustrated by experimental signals obtained from various scattering media like polymers, liquids and powders.     

Influence of synthesis temperature on the granulometric composition of a Ba0.65Sr0.35TiO3 pigment and the optical properties and radiation resistance of pigment-based coatings

The influence of synthesis temperature on the granulometric composition of a Ba_0.65Sr_0.35Ti O₃ pigment and the optical properties and radiation resistance of pigment-based coatings has been analyzed. It has been found that a rise in synthesis temperature decreases the sizes of pigment particles, deteriorates the reflectance of the coatings, and enhances their radiation resistance.     

基于多维漫反射光谱技术的复杂混合溶液成分检测

为了进行复杂混合溶液的成分检测,该文提出了一种基于多维漫反射光谱技术的浓度检测方式,通过信号中携带的不同成分的多种光学性质来进行分析。实验设计了基于超连续谱激光光源、精密电控平移台和光谱仪的检测装置,选用Intralipid-20%溶液作为研究对象,用蒸馏水配制体积百分数1%～20%的溶液,分别测量距其入射点1.5～13mm(间隔0.5mm)范围内的24点漫反射光谱信号,以偏最小二乘回归算法对单点和多点漫反射光谱信号进行建模与预测。得到建模精度最高的为距离入射位置最近的1点～13点对应的光谱信号所建立的模型,预测精度最高的为距离入射位置最近的1点～7点对应的光谱信号所建立的模型。结果表明,增加不同位置信息的光谱信号,能够提高光谱的信噪比,与传统光谱技术仅利用吸光度或反射率等单一光学性质的方法相比,增加了被测物质散射特性的影响,利用被测物质多种光学性质的变化提高了建模及预测的精度,为基于多维光谱的复杂混合溶液检测提供了基础。     

Plasmon based antireflection coatings containing nanostructured Ag and silica medium

The transmittance and scattering of the antireflection (AR) coatings based on nanostructured Ag and silica medium were enhanced by the exploitation of the localized surface plasmon resonance (LSPR). The transmittance and scattering values of AR coatings are relative to the annealing temperature, Ag concentration and thickness of AR coatings. The transmittance values of 95.7% and 97.2% of AR coatings with 0.10 wt.% Ag and annealed at 400 °C were obtained in the visible wavelength for a single-side and double-side coated glass slides, respectively. The enhanced transmittance and scattering of the AR coatings are primarily attributable to the large forward scattering of nanostructured Ag and the lesser refractive indices of Ag/SiO₂ coatings.     

Dielectric loss measurements on silver halide sheet crystals

Abstract

A series of studies on the partial X-ray diffuse scattering intensities from ternary alloys analysed through synchrotron radiation experiments has been reviewed. An intensity expression for the short-range order diffuse scattering has been developed, which is necessary in understanding the separation method of an observed X-ray diffuse intensity into partial intensities contributed from different origins. Techniques have been described in detail mainly concerning the Cu₂NiZn alloy, which have shown the benefits of the anomalous scattering effect of synchrotron radiation. The negative partial intensity maximum for the Cu-Ni pair found in the Cu-Ni-Zn alloy has been discussed from the viewpoints of crystallography and thermodynamics. In addition, at the end of the paper, local atomic arrangements causing the diffuse scatterings have been discussed.     

Common black coatings – reflectance and ageing characteristics in the 0.32–14.3 μm wavelength range

The diffuse and regular reflectances of five optically absorbing coatings frequently used in optical systems, were measured over the 0.32–14.3 μm wavelength range, before and after exposure to heat and intense optical radiation. The measured coatings included Nextel Velvet Black, an anodised coating and NPL Super Black. The anodised coating exhibited substantial variations in its diffuse and regular reflectance values after thermal and simulated solar ageing. Solar and thermal ageing of the Nextel Velvet Black resulted in increases of its reflectance. However, thermal ageing tended to decrease the reflectance of the other paint samples examined. Thermal and solar ageing of the NPL Super Black resulted in only minor changes in its reflectance characteristics. All measurements are traceable to the UK National Standards.     

Study on the Relationship between Particle Size and Near Infrared Diffuse Reflectance Spectroscopic Data

Since the particle size distribution is a critical parameter of pharmaceutical excipients used for tablet manufacturing by direct compression, the mean particle size of sieved sorbitol powder was studied by near‐infrared diffuse reflectance spectroscopy (NIRDRS). The aim of this study was to investigate the effect of the particle size (reciprocally proportional to the bulk density) on the reflectance spectrum. The effects of the particle characteristics on the spectral changes were described on the basis of the Kubelka‐Munk theory taking the scattering into consideration. A smaller particle size fraction was associated with a lower spectral value, and at the characteristic wavelength of 1584 nm a linear relationship was established for the particle size range from 125 to 670 μm. The diffuse reflectance measurement was sensitive to the particle characteristics, which offers a fast, non‐destructive alternative test method that can be applied after detailed calibration.     

Optimization and design of pigments for heat-insulating coatings

This paper reports that heat insulating property of infrared reflective coatings is obtained through the use of pigments which diffuse near-infrared thermal radiation.Suitable structure and size distribution of pigments would attain maximum diffuse infrared radiation and reduce the pigment volume concentration required.The optimum structure and size range of pigments for reflective infrared coatings are studied by using Kubelka-Munk theory,Mie model and independent scattering approximation.Taking titania particle as the pigment embedded in an inorganic coating,the computational results show that core-shell particles present excellent scattering ability,more so than solid and hollow spherical particles.The optimum radius range of core-shell particles is around 0.3 ～ 1.6 μm.Furthermore,the influence of shell thickness on optical parameters of the coating is also obvious and the optimal thickness of shell is 100-300 nm.     

Infrared radiative transfer modelling in a 3D scattering cloudy atmosphere: Application to limb sounding measurements of cirrus

The Monte Carlo cloud scattering forward model (McClouds_FM) has been developed to simulate limb radiative transfer in the presence of cirrus clouds, for the purposes of simulating cloud contaminated measurements made by an infrared limb sounding instrument, e.g. the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). A reverse method three-dimensional Monte Carlo transfer model is combined with a line-by-line model for radiative transfer through the non-cloudy atmosphere to explicitly account for the effects of multiple scattering by the clouds. The ice cloud microphysics are characterised by a size distribution of randomly oriented ice crystals, with the single scattering properties of the distribution determined by accurate calculations accounting for non-spherical habit.A comparison of McClouds_FM simulations and real MIPAS spectra of cirrus shows good agreement. Of particular interest are several noticeable spectral features (i.e. H₂O absorption lines) in the data that are replicated in the simulations: these can only be explained by upwelling tropospheric radiation scattered into the line-of-sight by the cloud ice particles.     

Scattering of Solar and Atmospheric Background Radiation from a Target

Light scattering property of environment is very important in theoretical study and application of the remote sensing. What's more, it is valuable for infrared radiation, imaging, and the detection of target and tracking. In this paper, solar and atmospheric background radiation, and their scattering property from target are discussed. BRDF (Biodirectional Reflectance Distribution Function) is a very important quantity that shows the radiation and reflection feature of target. According to electromagnetic radiant and scattering theories, the relationship between laser radar scattering cross section (LRCS) and BRDF is introduced. LOWTRAN model is an effective method of calculating the spectral distribution of solar and atmospheric radiation. Here it is applied to compute solar and atmospheric background radiation scattered from a target. The relative equations are deduced. Thus, the spatial and spectral distribution of scattering light is given. As a special example, for the Lambert's surface, the equations are simplified. As a result, the spatial and spectral distributions scattering radiation of solar and atmospheric background from a rough painted surface are present. The scattering of solar radiation plays a primary role in MIR region, but scattering of atmospheric background radiation is higher in LIR region. At the same time, there is obviously specular reflectance for solar radiation due to coherent scattering from rough surface.