Absolute thickness measurement of pyrolytic graphite spheroids by STEM-EELS

This paper studies the absolute thickness measurement of pyrolytic graphite spheroids (GSs) by using STEM-EELS mode with log-ratio method and Kramers-Kroning (K-K) method, taking the measured thickness from TEM image as reference that is the diameter of GSs ranging from 60 to 250 nm. The effect of collection semi-angle (β) on thickness measurement has been investigated. It is found that in general the thickness obtained by K-K analysis with surface effect corrected shows the best accuracy, followed by K-K sum rule and then log-ratio method for the three different collection semi-angles of 12.4, 17.3 and 21.1 mrad applied. Of these angles, the smallest one gives an overestimated result and the largest one gives an underestimated result, whereas between the two, the angle of 17.3 mrad that is about 2x convergence semi-angle (9.0 mrad) is identified as more appropriate for K-K analysis. The surface-scattering correction, inelastic mean free path of GS and effect of refractive index n on thickness measurement for different β angles are also investigated. Moreover, the optical property deduced from the data collected at the center of graphite spheroid, which is related to its microstructure, is characterized by K-K analysis.     

Optical and structural parameters of the ZnO thin film grown by pulsed filtered cathodic vacuum arc deposition

Transparent conductive ZnO film was deposited on glass substrate by pulsed filtered cathodic vacuum arc deposition (PFCVAD). Optical parameters such as absorption coefficient α, the refractive index n, energy band gap E_g and dielectric constants have been determined using different methods. Kramers-Kronig and dispersion relations were employed to determine the complex refractive index and dielectric constants using reflection data in the ultraviolet-visible-near infrared regions. The spectra of the dielectric coefficient were used to calculate the energy band gap and the value was 3.24 eV. The experimental energy band gap was found to be 3.22 eV for 357 nm thick ZnO thin film. The envelope method was also used to calculate the refractive index and the data were consistent with K-K relation results. The structure of the film was analyzed with an x-ray diffractometer and the film was polycrystalline in nature with preferred (002) orientation.     

块状及粒子煤灰复折射率的研究

1引言燃煤锅炉内的粒子（如焦碳、碳黑、飞灰粒子）及块状的燃烧产物（如积灰、结渣等）参与炉内辐射换热。这些固态物质的辐射特性，是炉内辐射换热计算的重要参数，而复折射率（。一n－7幼是确定这些参数的基本物性数据。复折射率不能直接测量，需要通过测量其它量，用反问题计算方法才能得到。目前；国际上求煤灰粒子复折射率的计算方法主要有两类：（1）直接利用煤灰粒子做实验［‘头（2）利用块状煤灰实验求其复折射率，认为它等于煤灰粒子的复折射率［’－‘］。D．R．Huffman问在理论上证明，二者的复折射率将会有所不同。本文分别…     

Determination of refractive indices of liquids by Fresnel diffraction

We demonstrate an easy, reliable, applicable, and sensitive method to measure refractive index of liquids by using Fresnel diffraction. In this method a cylindrical glass rod, in general, or an optical fiber in special case, is immersed into a liquid. Physical parameters of the rod, like radius and refractive index, should be well known. Then, the normalized intensity distribution on the Fresnel diffraction pattern of a plane wave diffracted from the immersed fiber is measured. Thereafter, refractive index of the liquid is evolved by the least-square method. This method applied to determine the refractive index of four liquids; pure water, 2-propanol (isopropanol), acetone and methanol. Index of refraction of each one has been acquired for four visible wavelengths. A theoretical approach and experimental results is presented.     

Temperature-dependent optical properties of GaSe layered single crystals

Optical properties of GaSe single crystals have been investigated using temperature-dependent transmission and room temperature reflection measurements in the wavelength range of 380–1100 nm. The analysis of the absorption data at room temperature showed the existence of indirect transitions in the crystal with energy band gap of 1.98 eV. Temperature dependence of the transmission measurements revealed the shift of the absorption edge toward lower energy as temperature is increased from 10 to 280 K. The rate of change of the indirect band gap was found as γ = ?6.6 × 10^?4 eV/K from the analysis of experimental data under the light of theoretical relation giving the band gap energy as a function of temperature. The absolute zero value of the band gap energy and Debye temperature were calculated from the same analysis. The Wemple–DiDomenico single-effective-oscillator model applied to refractive index dispersion data was used to determine the oscillator energy, dispersion energy, oscillator strength and zero-frequency refractive index values.     

Light propagation in porous ceramics: porosity and optical property studies using tunable diode laser spectroscopy

By integrating gas in scattering media absorption spectroscopy and frequency domain photon migration a new method is developed for the study of optical porosity and optical properties of porous media, in our case ceramics. The optical porosity is defined as the ratio of the path length through the gas-filled pores and the physical path length through the whole medium. The effective refractive index of the porous ceramics is also retrieved based on the optical porosity, which is then used to evaluate the reduced scattering coefficients of the porous ceramics. The combined method provides a new way to study light propagation in porous media. A modified Looyenga model is proposed to study the relationship between the physical porosity and the effective refractive index of the porous medium, which also connects the optical and physical porosities, and provides the possibility to use the present method for porosimetry analysis.     

Optical refractometry based on Fresnel diffraction from a phase wedge

A method that utilizes the Fresnel diffraction of light from the phase step formed by a transparent wedge is introduced for measuring the refractive indices of transparent solids, liquids, and solutions. It is shown that, as a transparent wedge of small apex angle is illuminated perpendicular to its surface by a monochromatic parallel beam of light, the Fresnel fringes, caused by abrupt change in refractive index at the wedge lateral boundary, are formed on a screen held perpendicular to the beam propagation direction. The visibility of the fringes varies periodically between zero and 1 in the direction normal to the wedge apex. For a known or measured apex angle, the wedge refractive index is obtained by measuring the period length by a CCD. To measure the refractive index of a transparent liquid or solution, the wedge is installed in a transparent rectangle cell containing the sample. Then, the cell is illuminated perpendicularly and the visibility period is measured. By using modest optics, one can measure the refractive index at a relative uncertainty level of 10(-5). There is no limitation on the refractive index range. The method can be applied easily with no mechanical manipulation. The measuring apparatus can be very compact with low mechanical and optical noises.     

Finite-bandwidth effects on the causal prediction of ultrasonic attenuation of the power-law form

Kramers-Kronig (K-K) relations exist as a consequence of causality, placing nonlocal constraints on the relationship between dispersion and absorption. The finite-bandwidth method of applying these relations is examined where the K-K integrals are restricted to the spectrum of the experimental data. These finite-bandwidth K-K relations are known to work with resonant-type data and here are applied to dispersion data consistent with a power-law attenuation coefficient (exponent from 1 to 2). Bandwidth-restricted forms of the zero and once-subtracted K-K relations are used to determine the attenuation coefficient from phase velocity. Analytically, it is shown that these transforms produce the proper power-law form of the attenuation coefficient as a stand-alone term summed with artifacts that are dependent on the integration limits. Calculations are performed to demonstrate how these finite-bandwidth artifacts affect the K-K predictions under a variety of conditions. The predictions are studied in a local context as a function of subtraction frequency, bandwidth, and power-law exponent. The K-K predictions of the power-law exponent within various decades of the spectrum are also examined. In general, the agreement between finite-bandwidth K-K predictions and exact values grows as the power-law exponent approaches 1 and with increasing bandwidth.     

色散、群速与群折射率

本文讨论了群折射率存在的物理意义,指出群折射率不仅包含了折射率概念而且还体现了折射率的色散性质,同样能作为材料本身的光学性质参量.接着指出在折射率的白光干涉法测量中存在着忽视色散作用而导致的将群折射率误认为折射率的情况.将群折射率与折射率区别开来,不仅可以消除折射率测量中所存在的错误,而且可以突出色散现象在光传播时间特性上的意义.为此建立了折射率与群折射率的相互变换关系,通过对于典型物质的折射率与群折射率变换关系的计算,说明二者在数值上的差别甚至对于气体介质来说也是不能忽略的.     

梨花粉红外波段复折射率测定与分析

花粉是生物气溶胶重要的组成部分,复折射率是研究花粉光学特性以及探测、识别生物气溶胶成分的重要参数。采用压片法对梨花粉2.5~15 μm波段的反射光谱进行了测量,利用Krames-Kronig(K-K)关系计算了复折射率,并就傅里叶红外光谱仪测试压片的入射角和复折射率长波长、短波长区外推两方面对结果作了误差分析。结果表明,测试时18°入射角以及长波长、短波长区外推对梨花粉复折射率的计算结果影响不大,利用反射光谱计算花粉复折射率的方法是可行的。计算得到的复折射率谱对梨花粉光学特性的研究以及生物气溶胶成分的探测、识别有一定的参考价值。     

微生物远红外波段复折射率测定及模型构建

选择枯草芽孢杆菌、黑曲霉孢子和黑曲霉菌丝体等3种典型微生物制备生物样品, 采用显微红外光谱仪对3种微生物样品在2.5—15 μm波段的红外反射光谱进行测定, 基于Kramers-Kronig (K-K)关系计算得到了微生物样品在6—14 μm波段的复折射率. 以水、蛋白质和核酸的红外吸收特性为基础,根据微生物样品的 红外吸收谱线计算了微生物样品含水量. 在3种微生物远红外波段复折射率和含水量的实测数据基础上, 构建了生物颗粒在6—14 μm远红外波段的复折射率模型, 分析了模型的可靠性. 模型的构建对发展生物样品的快速分析、鉴定方法, 进而推动生物气溶胶探测、识别技术进步具有重要意义. 关键词： 光学参数 微生物复折射率模型 远红外波段     

中红外散射的基质折射率效应研究

本文利用Mie散射理论对中红外波段三种不同类型散射体的散射和消光进行了研究,发现基质在三种不同类型散射体的散射和消光中所起作用完全不同。对于无吸收的高折射率散射体,基质折射率越大面积散射比(或面积消光比)越低;对于反常色散散射体,基质折射率越大面积散射比和面积肖光比越高;而对于金属散射体,基质折射率的大小对于散射和消光影响极小。     

Cauchy's dispersion equation reconsidered: Dispersion in silicate glasses

We formulate a novel method of characterizing optically transparent substances using dispersion theory. The refractive index is given by a generalized Cauchy dispersion equation with coefficients that are moments of the uv and ir absorptions. Mean dispersion, Abbé number, and partial dispersion are combinations of these moments. The empirical relation between index and dispersion for families of glasses appears as a consequence of Beer's law applied to the uv spectra.     

Influence of spatial dispersion of the first and the second orders simultaneously on the parameters of natural waves in a uniaxial crystal

It is found for the first time that the coexistence of two principal and two additional natural waves and only one additional wave (in the absence of the second one) is impossible in the exact solution and in the approximate solution, respectively, of the problem formulated in the title, because Fresnel’s general equation beaks up into two independent equations for two principal and two additional waves. A probable relationship is found between the small parameters of spatial dispersion of the first (γ) and the second (α₀) orders (α₀/γ≈1) for the spectral region far from resonances, for which the refractive index of the third additional wave for α₀=0 is approximately equal to the refractive index of one of two additional waves for α₀≠0 and γ≠0, when the wave normal is directed along the optical axis of a uniaxial crystal.     

发光光弹性涂层折射率测量方法

涂层的折射率是发光光弹性涂层方法采用斜射法应变分离时不可缺少的参数之一. 通过对发光光弹性涂层受斜入射光波激发时, 发射光波沿入射光波原路径返回振幅变化的理论分析, 提出一种基于发光涂层光学菲涅耳响应的折射率在线测量方法. 实验测量了罗丹明B为发光染料的发光光弹性涂层在入射角为60°、波长为465 nm光波激发下的涂层折射率. 测量结果表明: 新的折射率测量方法是可行的, 对于其他用途的发光涂层折射率测量同样适用. 关键词： 折射率 光学测量 光学涂层 光致发光     

同轴电介质-金属-电介质结构表面等离激元色散研究

从平面电介质-金属薄膜-电介质对称结构中表面等离激元的色散方程出发,建立模型推导得到了同轴电介质-金属薄膜-电介质结构中表面等离激元的色散方程,在这种结构中各阶模式都发生了分裂,形成了高折射率高损耗和低折射率低损耗的两种模式,该模型为理解同轴电介质-金属薄膜-电介质结构表面等离激元模式的传播提供了直观的图像。用色散方程计算了0.5～1.5μm波长范围内各阶模式的等效折射率以及传输损耗,并将该结果与有限元方法数值模拟得到的结果进行对比分析,分析表明,两者吻合得很好。并分析了计算结果以及色散方程的适用范围。     

Turbidity Spectra of Polymeric-Monomeric Particles Formed on Emulsion Polymerization of Acrylates

The possibility of applying the turbidity-spectrum method and the conditions of its application in kinetic investigations of emulsion polymerization are discussed. The necessity of taking into account the spectral dependence of the refractive index of polymeric-monomeric particles and of a dispersion medium and multiple secondary light scattering as well as of using approximating analytical expressions for the characteristic functions of light scattering is noted, because the refractive index of scattering centers depends on the polymerization depth. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 3. pp. 313–316, May– June, 2005.     

Determination of the effective refractive index of porous silicon/polymer composite films

The equation for calculating the effective refractive index of porous silicon inserted polymer was obtained by three-component Bruggeman effective medium model. The dependence of the effective refractive index of porous silicon/polymer composite films on the polymer fraction with various initial porosity was given theorically and experimentally respectively. The porous silicon and polymer polymethylmetacrylate based dispersive red one (PMMA/DR1) composite films were fabricated in our experiments. It is found that the measured effective refractive index of porous silicon inserted polymer was slightly lower than the calculated result because of the oxidization of porous silicon. The effective refractive index of oxidized porous silicon inserted polymer also was analyzed by four-component medium system.     

有机材料在各种波长的折射率计算

使用Vogel方法和介质的色散关系,计算有机化合物在各波长的折射率n(λ).用Vogel方法把化合物分子分解成碎片,加和得到化合物在某几个波长的折射率.假设化合物在所计算的波长范围内为正常色散关系,使用Voyel方法得到的两个折射率,通过Cauchy公式得到色散曲线,从而得到各波长的折射率n(λ).通过对有机化合物芪盐和高分子材料聚苯乙烯的各波长折射率进行计算,并与材料在某一特定波长的实际折射率对比,证明了计算结果比较准确.并对双折射液晶材料的折射率计算进行了探索.