Measuring the refractometric characteristics of optical plastics

Ten types of American, Japanese, and German optical plastic (OP) materials are examined. The principal OPs are analysed: polymethyl methacrylate, polystyrene, polycarbonate, and styrene acrylonitrile. Refractive indices are measured and calculated for the principal and some new applicable OPs, namely NAS-21 Novacor, CTE-Richardson, Zeonex E48R, Optorez 1330 and Bayer for wavelengths from 435.8 to 1052 nm. A theoretical examination was made for computer modelling of OPs indices using Cauchy's dispersion formula. The dispersion coefficients and Abbe constants are calculated. The OPs indices computed for numerous laser wavelengths 442–1060 nm are presented. A more effective device and technology for the measurement of refractive index of OPs is realized with an accuracy of ±0.001.     

热压载荷作用下气体检测光学窗口对激光传输影响

采用有限元方法研究了不同热压载荷作用下多组分气体原位激光检测系统的光学窗口变形分布情况,并根据热光效应计算得到光学窗口折射率分布。采用光线追迹法对比分析了氮气吹扫前后光学窗口折射率变化及变形对到达接收面的通光量和辐照度分布影响规律。此外,基于高温光学窗口激光透射测试平台开展了高温光学窗口对检测信号影响研究。结果表明:高温高压环境会使光学窗口折射率变化幅度增大及变形加剧,导致激光光路偏折引起透射光强损耗和探测信号条纹干涉;氮气吹扫可以有效改善激光传输条件,增加到达接收面的通光量,优化辐照分布,提高激光传输质量。     

The composition and optical absorption coefficient of atmospheric particulate matter

The optical absorption spectra of atmospheric dust as determined by transmission and diffuse reflectance spectroscopic methods is discussed in the 0.4 to 40 um wavelength range. Quantitative measurements are presented which show the imaginary refractive index to be about 0.007i, with little wavelength dependence, in the 0.4 to 1.3 μm spectral interval. The absorption coefficients of individual materials found in atmospheric dust are also given. This work suggests that atmospheric dust may be composed mainly of weakly absorbing particles contaminated with small amounts of very strongly absorbing materials such as free carbon. The implications of this are discussed from the point of view of laser beam attenuation and lidar return signals. Mie theory computations for ruby lidar wavelengths are shown which suggest that for some models of atmospheric dust, the concept of an average imaginary refractive index may be misleading. Thus, it may be necessary to consider the individual complex refractive indices and size distributions of more than one constituent material present in the dust. This implies that anthropogenic contributions to the atmospheric aerosol, such as free carbon and other strong absorbers, may be of greater optical significance than their relative concentrations might indicate.     

Size-dependent nonlinear optical properties and thermal lens in silver nanoparticles

We have investigated the nonlinear response of the silver nanoparticle samples in a low-power regime of electromagnetic field based on nonlocal thermo-optic models. In this work, the experimental investigation of the thermo-optic nonlinear response of Ag colloids containing different size of silver nanoparticles is reported. The colloidal nanoparticle samples were synthesized by nanosecond pulsed laser ablation of Ag bulk in acetone. The sample containing Ag was characterized by linear absorption spectroscopy and transmission electron microscopy. Using the z-scan technique, the behavior of thermal nonlinear refractive index of colloid was studied at different concentrations of silver nanoparticles. Observation of asymmetrical configurations of the z-scan data indicates that nonlinear refraction occurring in the Ag samples is related to the thermo-optical process. The optical limiting here is due to nonlinear refraction of the samples arising from thermal lens formation under low-power CW excitation. When the laser power is low, the self-defocusing effect is mainly dominated by surface plasmon resonance effect. Results show that with increasing concentration of nanoparticles in acetone, the nonlinear refractive index increases while the threshold power of optical limiting decreases.     

Refractive,dispersive and thermo-optic properties of twelve organic solvents in the visible and near-infrared

We report on experimental measurements of the refractive index of twelve organic solvents at five different wavelengths (450, 532, 632.8, 964 and 1,551 nm) and a temperature of 300 K. Based on these new data visible to near-infrared dispersion relations are constructed. Group-velocity dispersion (GVD) is theoretically calculated. Zero- and negative-GVD situations are identified for two common solvents in near-infrared wavelengths. Via comparison with refractive index data available in bibliography, estimated values of thermo-optic coefficients are also presented.     

A method of precise determination of the optical constants of uniaxial crystals from the compensator parameters

A method of determination of the refractive indices of uniaxial crystals from the compensator parameters is proposed. In this case, the accuracy is limited by the temperature fluctuations inside a crystal. The orientation of the optical axis with respect to the surface and the thickness and the thermal expansion coefficient of the crystal can be determined additionally. This method can be used for precise determination of the refractive indices and absorption coefficients of biaxial crystals. Experimental results of determination of the temperature coefficients of the refractive indices and of linear expansion for a plane-parallel plate cut from artificial crystalline quartz parallel to the optical axis are presented.     

On the problem of calculating the optical film parameters from the measured transmission spectra

The procedure for calculating the dispersion of the refractive and absorption indices and thickness of an optical film, based on measurements of spectral dependence of the transmittance, is described. The film parameters are calculated using a solution of the approximation problem. The effect of the film model on the calculated values of the refractive and absorption indices is analyzed.     

Study of optical constants of PbTe and GeTe films

Results of studying the absorption coefficients and refractive indices of PbTe and GeTe films in the spectral range from 1 to 15 μm are presented. The optical constants of films were found by a technique that combines calculation methods and the presence of strong absorption bands in the spectra. The spectral intervals were determined where the film-forming materials under consideration offer promise in the production of interference coatings for the IR spectral region.     

Widely tunable asymmetric long-period fiber grating with high sensitivity using optical polymer on laser-ablated cladding

We demonstrate high-efficiency, wideband-tunable, laser-ablated long-period fiber gratings that use an optical polymer overlay. Portions of the fiber cladding are periodically removed by CO(2) laser pulses to induce periodic index changes for coupling the core mode into cladding modes. An optical polymer with a high thermo-optic coefficient with a dispersion distinct from that of silica is used on a deep-ablated cladding structure so that the effective indices of cladding modes become dispersive and the resonant wavelengths can be efficiently tuned. The tuning efficiency can be as high as 15.8 nm/ degrees C, and the tuning range can be wider than 105 nm (1545-1650 nm).     

Piezoelectric lattice vibrations at optical frequencies

A relationship is proposed between the piezoelectric coefficient and the dielectric constant (or refractive index) based on classical dispersion theory. Piezoelectric lattice vibrations are associated with ionic polarizations at optical frequencies. This relation is applied to study the piezoelectric lattice vibrations in α-quartz, and agreement is found between the calculated and the measured value of the piezoelectric coefficient. No direct experimental method for measurement of piezoelectric coefficients at optical frequencies exists; however, in terms of the proposed relation, piezoelectric coefficients at optical frequencies can be evaluated from infrared reflection measurements.     

Modeling and analysis of quadruple optical ring resonator performance as optical filter using Vernier principle

Vernier principle based modeling and analysis of an optical ring resonator structure that includes four asymmetric rings are introduced in this paper to obtain very wide free spectral range (FSR). Delay line signal processing approach in Z-domain modeling is used for analysis of waveguide based novel quadruple optical ring resonator (QORR). Two QORR architectures made of SOI and SiN waveguides have been compared, which produce FSR of 343.4 THz 264.6 THz respectively. Apart from obtaining wider FSR and adequate suppression of spurious interstitial modes close to -30 dB, this work presents group delay and dispersion characteristics for QORR made of materials with different effective refractive indices.     

Kramers-Kronig relations and sum rules of negative refractive index media

Negative refractive index media have become a hot topic in physics due to their proposed revolutionary properties, which would have drastic consequences in design of novel optical devices. We show that Kramers-Kronig relations connecting the real and imaginary parts of the complex refractive index of absorbing media are valid even though the real refractive index may take negative value at some spectral range. In addition universal sum rules for linear optical constants of negative index media are also valid. This means that negative refractive index media are not fundamentally different from regular media. Hence, any spectrum measured from negative refractive index media can be analyzed using dispersion relations and sum rules, which have so far provided information on the optical properties of materials.Received: 13 May 2004, Published online: 30 September 2004PACS: 77. Dielectrics, piezoelectrics, and ferroelectrics and their properties - 78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)     

氟化铒薄膜晶体结构与红外光学性能的关系

使用热蒸发技术在锗(111)衬底上制备了氟化铒(ErF₃)薄膜. XRD衍射结果表明，随着衬底温度的增加，氟化铒薄膜发生了从非晶状态到结晶状态的转变，薄膜的表面形貌和红外光学性能也发生了显著的变化，部分结晶的氟化铒薄膜的远红外透射谱和完全非晶的薄膜基本一致，但是与结晶薄膜则没有相似之处. 晶格常数计算表明薄膜中存在压应力. 使用洛伦兹谐振子模型对薄膜的透射率曲线进行拟合计算，得到ErF₃薄膜的折射率和消光系数. 在10μm处非晶薄膜的折射率和消光系数最小值分别为1.38和0.01，结晶薄膜的折射率和消光系数最小值分别为1.32和0.006. 关键词： 氟化铒 红外光学性质 光学常数 洛伦兹谐振子模型     

基于磁流体填充微结构光纤的温度特性研究

利用毛细现象将磁流体完全填充到六角形微结构光纤的空气孔中, 分析了磁流体填充长度、浓度对其传导特性的影响. 结合磁流体独特的热光效应, 并对一定浓度、长度下填充的光纤进行了温度特性的研究. 结果表明, 随着温度的升高, 透射谱1460 nm处磁流体的吸收峰逐渐变浅. 基于磁流体载液与表面活性剂对温度的不同敏感性, 吸收峰左右两个边沿表现出不同的温度响应; 在波长为1100–1700 nm之间透射损耗与温度变化成线性关系, 对于填充长度为10 cm的微结构光纤, 敏感度达到0.06 dB/℃, 且液体填充长度越长, 灵敏度越高. 该研究将微结构光纤与磁流体材料有机地结合起来, 并利用填充材料自身的热光特性, 实现了对透射谱的单边调谐, 将其作为热光可调谐器件、滤波器等相关可调谐光子器件在光通信、 光传感等领域将具有很大的应用潜力. 因此, 基于材料填充微结构光纤的研究可为探索新型全光纤光子器件的新技术和新结构提供有效的方法. 关键词： 微结构光纤 磁流体 热光效应 温度传感     

Polaron effects on the optical absorption coefficients and refractive index changes in a square quantum well

The linear and nonlinear optical absorption coefficients and refractive index changes are obtained by using the compact density-matrix approach and an iterative procedure. With typical semiconducting GaAs materials, the linear, third-order nonlinear, total optical absorption coefficients and the optical refractive index have been examined. We find that the polaron effect has an important influence on the linear, third-order nonlinear, and total absorption coefficients as well as the refractive index changes.     

Dispersion modified slot optical waveguides

Advent of slot waveguide structures had opened a new era where light can be confined in low index slot guarded by high index slabs. Already in use SOI slot waveguides (contrast ratio is 2.42) have two distinct properties over the conventional waveguides, i.e. high E-field amplitude, optical power, optical intensity in low index materials, and strong E-field confinement localized to nanometer-size low index regions. We hereby propose a low refractive index contrast ratio slot waveguide structure (ratio is 1.18) comprising of commercially available glass material. Novelty lies in showing high E-field amplitude, optical power, optical intensity, and strong E-field confinement in low index slot regions despite of lowest ever reported contrast ratio. A systematic numerical study on the higher order dispersion characteristics of the widely studied SOI-based slot structure and of our proposed low refractive index contrast slot structure is carried out. It has been demonstrated that low refractive index contrast ratio slot optical waveguide GVD properties are quite different than SOI slot optical waveguide. The less normal dispersion existing in this kind of waveguide could have an impact on their applications in various nonlinear or linear applications.     

基于透射光谱确定溅射Al2O3薄膜的光学（已撤稿）

基于反应磁控溅射Al₂O₃薄膜的紫外—可见—近红外透射实验光谱,采用Swanepoel方法结合Wemple-DiDomenico色散模型,方便地导出了Al₂O₃薄膜在200—1100 nm波长范围内的光学常数,包括折射率、色散常数、膜层厚度、吸收系数及能量带隙.研究发现反应磁控溅射Al₂O₃薄膜具有高折射率(1.556— 1.76,测试波长为550 nm)、低吸收和直接能量带隙(3.91—4.20 eV)等光学特性,而且其光学常数对薄膜制备过程中的重要工艺参数——膜层后处理温度表现出强烈的依赖性.此外,在膜层的弱吸收和中等吸收光谱区域内,计算得到的折射率色散曲线与分光光度法的测试结果基本符合,说明本实验中所建立的计算方法在确定反应磁控溅射Al₂O₃薄膜光学常数方面的可靠性. 关键词： 光学常数 Swanepoel方法 2O₃薄膜')" href="#">Al₂O₃薄膜 热处理     

玻璃基板中热光效应折射率分布的研究和测定

几乎所有的光学材料都具有热致折射率变化的特性,当光束经过局域热源作用下折射率呈梯度分布的介质时会发生偏向,利用这种特性可做成各种热光器件.本文在玻璃基板表面上制备了条形Ti薄膜热源,通过测定出射光束的偏向角,利用解折方法,得出基极截面的折射率分布.根据能量守恒,得到该材料的折射率温度系数,与公布值比较,验证了本方法的正确性.本文对研究和分析热光材料和器件提供了一种有益的方法.     

Measurements of Building Construction Materials at Ka-Band

Millimeter waves is expected to be used for indoor broadband wireless access for its rich frequency spectrum resources. To implement the indoor MMW wireless system, it is important to know its propagation characteristics in building, which are governed by the transmission properties of construction materials. This paper focuses on the measurements of reflection characteristics and refractive indices of some interior construction materials (such as glass, brick, plasterboard, silencing board, etc.) at Ka–band. The free–space reflection method was used to measure the reflection and transmission coefficients. Then the complex refractive indices of various materials could be calculated by using the Fresnel's formula.