Procedure for retrieving the optical properties of a two-layered medium from time-resolved reflectance measurements

A procedure for retrieving the optical properties of a two-layered diffusive medium based on an exact analytical solution of the diffusion equation and on relative multidistance time-resolved reflectance measurements is presented. The method overcomes some limitations of previously developed procedures. Five parameters of the medium have been fitted: the absorption and the reduced scattering coefficients of both layers and the thickness of the first layer. The actual values of the parameters are correctly retrieved by the procedure. The inversion procedure does not require an initial guess for the unknown optical properties, but the starting value for the thickness of the first layer needs to be estimated with an error smaller than 50%.     

基于表观光谱反演黄东海水体固有光学量研究

水色遥感反演算法中半分析模型的建立需要已知水体同有光学量,文章基于现场实测数据建立了由遥感反射率反演同有光学量模型.对2003年春季黄东海航次所测数据进行了介绍,详细阐述了遥感反射率、颗粒物后向散射和吸收系数的测量方法.基于生物光学模型,利用单纯形优化算法由遥感反射率来反演水体同有光学量,并将反演结果与实测数据进行了比...     

Inversion of the nonlinear equations of reflection ellipsometry on film-substrate systems

We discuss an inversion procedure to determine the optical properties and film thickness of a transparent film on an absorbing substrate system. The determination of optical properties of the film and substrate are separated from that of the film thickness. An error analysis is presented for the special case of multiple-angle-of-incidence ellipsometry for the SiO₂-Si system at λ = 6328 Å.     

Negative index of refraction in optical metamaterials

A double-periodic array of pairs of parallel gold nanorods is shown to have a negative refractive index in the optical range. Such behavior results from the plasmon resonance in the pairs of nanorods for both the electric and the magnetic components of light. The refractive index is retrieved from direct phase and amplitude measurements for transmission and reflection, which are all in excellent agreement with simulations. Both experiments and simulations demonstrate that a negative refractive index n' approximately -0.3 is achieved at the optical communication wavelength of 1.5 microm using the array of nanorods. The retrieved refractive index critically depends on the phase of the transmitted wave, which emphasizes the importance of phase measurements in finding n'.     

Multivariate analysis of multiple impedance spectra

A one-step method for evaluation of multiple impedance measurements in a multivariate analysis is presented. Usually two steps are necessary to extract model parameters like activation energy from impedance measurements at two or more temperatures. First, each measurement is analyzed with CNLS (complex nonlinear least squares) software using the same equivalent circuit. Second, activation energy is obtained in a NLS fit of conductivity data. This two-step procedure could lead to doubtful results as fit errors because of noise in the first step could prevent reliable results in the second step. Error estimates of model parameters are only based on the second step, ignoring the quality of the first step. Using a one-step method, model parameters are directly obtained from multiple impedance measurements, often resulting in more reliable results and meaningful error estimates than for the two-step procedure. Similar approaches to the one proposed have been reported in literature. Although some approaches are reported to be implemented in a software package, none of these are available to the community. The aim of this paper is to clearly point out the mathematics used and the benefits of a simultaneous analysis of impedance spectra.     

Cost Optimized Non-Contacting Experimental Modal Analysis Using a Smartphone

The vibrations behavior analysis is an essential step in the mechanical design process. Several methods such as analytical modelling, numerical analysis and experimental measurements can be used for this purpose. However, the numerical or analytical models should be validated through experimental measurements, usually expensive. This paper introduces an inexpensive smartphone as an accurate, non-intrusive vibrations’ behavior measurement device. An experimental measurement procedure based on the video processing method is presented. This procedure allows the measurement of the natural frequencies and the mode shapes of a vibrating structure, simply by using a smartphone built-in camera. The experimental results are compared to those obtained using an accurate analytical model, where the natural frequencies error is less than 2.7% and the modal assurance criterion is higher than 0.89. In order to highlight the obtained results, a comparison has been done using a high quality and high frame per second (fps) camera-based measurement of material properties. Since the highest recovered natural frequency and its associated mode shape depend on the frame per second rate of the recorded video, this procedure has great potential in low frequencies problems such as for big structures like buildings and bridges. This validated technique re-introduces the personal smartphone as an accurate inexpensive non-contacting vibration measurement tool.     

Review of the characteristic effective medium approximation: Fundamentals and use in calculating the optical properties of ultrathin layer structures

This article presents a review of several aspects of the characteristic effective medium approximation that has been used to calculate the optical properties of ultrathin multilayer systems treated as one uniform layer with a single set of effective optical constants. The method, applied for normal incidence, enables one to represent any layer stack by one characteristic matrix whose elements are functions of the structure effective optical constants, stack thickness, and wavelength of the incident light wave. The error between values of the optical properties of a layer system calculated by the standard characteristic matrix technique and those calculated by the characteristic effective matrix approximation can be used as a criterion for establishing a limit beyond which the validity of the approximation could be compromised. As part of this grand review, calculations of the optical properties for normal incidence for numerous layer systems that were reported earlier in separate communications, are reviewed and analyzed.     

Improved contrast polymer light-emitting diode with optical interference layers

An improved contrast polymer light diode based on the destructive optical interference layers deposited between the glass substrate and ITO anode is fabricated. It is unnecessary to be considered that the additional optical interference structure will impede carrier injection from the electrode to the carrier-transporting layer. Due to the quarter-wavelength thickness of medial ITO layer, the reflected light from first Cr layer is inverted 180° out of phase with the reflected light from second Cr layer, resulting in the destructive interference. It is evident that the contrast ratio of the device with the optical interference structure is about three times higher than that of the conventional device.     

基于O2-O2吸收的非相干宽带腔增强吸收光谱浓度反演方法研究

针对传统非相干宽带腔增强吸收光谱浓度反演方法的定量结果易受镜片反射率标定误差的影响问题, 提出了一种基于测量大气O₂-O₂吸收的浓度反演方法. 该方法是将非相干宽带腔增强吸收光谱技术的光学增强腔等效成吸收光程不随波长变化的多次反射池, 首先根据测得的宽带腔增强大气吸收谱和参考谱计算出光学厚度, 并应用差分光学吸收光谱算法拟合修正后的气体吸收截面到光学厚度, 反演得到大气中O₂-O₂以及被测气体的柱浓度, 然后根据O₂-O₂在大气中的含量已知且相对稳定这一特性, 确定出等效多次反射池的吸收光程, 最后从被测气体的柱浓度中扣除吸收光程信息得到被测气体的浓度值. 以监测大气中NO₂实验为例, 应用该方法在454-487 nm波段反演得到了大气NO₂的浓度(1-30 ppbv范围内), 并将反演结果与传统浓度反演方法的结果进行了对比, 发现两者的不一致性在7%以内. 实验结果表明, 非相干宽带腔增强吸收光谱技术可以利用大气O₂-O₂的吸收来定量其他被测气体的浓度, 而且定量结果对镜片反射率的标定误差不敏感.     

Aerosol extinction coefficient profile retrieval in the oxygen A-band considering multiple scattering atmosphere. Test case: SCIAMACHY nadir simulated measurements

A multiple scattering inversion procedure for the aerosol extinction coefficient profile retrieval and error assessment in the oxygen A-band, for passive remote sensing instruments, has been developed. The procedure has been applied to SCIAMACHY nadir simulated measurements to investigate its effectiveness in the troposphere.The inversion procedure consists of a multiple scattering Forward Model, an inversion method and a complete sensitivity and error assessment tool. The Forward Model is based on LIDORT code; the inversion method, the sensitivity study and the complete error assessment are based on Optimal Estimation. The sensitivity and error analysis has been derived to investigate the profile retrieval errors due to the uncertainty of different aerosol optical properties, molecular and surface parameters.The analysis confirms that the profile retrieval accuracy and vertical resolution are strongly dependent on the oxygen A-band spectral resolution. The moderately high SCIAMACHY spectral resolution (0.4 nm in the oxygen A-band) results in distinguishing a maximum of three aerosol layers in troposphere. The SCIAMACHY tropospheric aerosol profile retrieval is shown to be highly sensitive to aerosol optical properties as phase function and single scattering albedo. The sensitivity study reveals an improvement of information content increasing the solar zenith angle and decreasing the surface albedo. As regards the forward model, negligible errors occur as the number of streams exceeds 6.     

聚乙烯醇/二氧化硅复合增透膜的制备和可清除性

 用溶胶-凝胶法制备了易清洗的聚乙烯醇/二氧化硅(PVA/SiO₂)复合增透膜。先在K9玻璃基片上镀制PVA薄膜,然后在PVA薄膜上镀上二氧化硅增透膜。用紫外可见光分光光度计、椭偏仪、光学显微镜、扫描探针显微镜和静滴接触角测量仪分别分析了膜层和基片的透射率、膜层厚度和折射率、表面形貌、水接触角等性质,用去离子水作溶剂对复合膜层进行清洗。结果表明：聚乙烯醇/二氧化硅复合增透膜峰值透射率达到99.8％,峰值透射率位置可以随SiO₂厚度而调节。复合膜层能够被热水清除,清除后基片完好,其透射率、表面形貌和水接触角与镀膜前一致。     

Evaluation of dual differential absorption lidar based on Raman-shifted Nd:YAG or KrF laser for tropospheric ozone measurements

Based on Raman-shifted Nd:YAG or KrF laser, a method of three-wavelength Dual DIfferential Absorption Lidar (DIAL) for tropospheric ozone measurements is proposed. A theoretical analysis and numerical simulations of the measurement error have been performed. The results show that this method can reduce the error in ozone measurements caused by the aerosol layer in the troposphere by a factor of ten. The proposed method is also shown to be insensitive to aerosol optical properties, and therefore, one does not need to know the wavelength dependence of aerosol scattering. The dual-DIAL with 277.1, 291.8, 313.2 nm radiation based on a Raman-shifted KrF laser can be used both during day- and night-time. The dual-DIAL with 289.0, 299.1, 316.1 nm radiation based on Raman-shifted Nd:YAG laser can only be used during night-time.     

Pulse‐shape instabilities and their measurement

Multi‐shot pulse‐shape measurements of trains of ultrashort pulses with unstable pulse shapes are studied. Measurement techniques considered include spectral‐phase interferometry for direct electric‐field reconstruction (SPIDER), second harmonic generation frequency‐resolved optical gating (FROG), polarization gate FROG, and cross‐correlation FROG. An analytical calculation and simulations show that SPIDER cannot see unstable pulse‐shape components and only measures the coherent artifact. Further, the presence of this instability cannot be distinguished from benign misalignment effects in SPIDER. FROG methods yield a better, although necessarily rough, estimate of the pulse shape and also indicate instability by exhibiting disagreement between measured and retrieved traces. Only good agreement between measured and retrieved FROG traces or 100% SPIDER fringe visibility guarantees a stable pulse train.     

On initialization,error and flux conservation in the doubling method

Truncation errors and flux conservation errors in the doubling method are examined. The error properties of five different initial-layer approximations are compared as a function of initial-layer size, layer optical depth, single-scattering albedo, and phase function asymmetry parameter. The “diamond” initial-layer approximation is found to be orders of magnitude more accurate than the others for fixed initial-layer size, or of equivalent accuracy starting from a very much larger initial layer. The commonly used single-scattering initialization is shown to lead to serious flux conservation errors. Analytic error estimates, based upon a new derivation of the single-scattering initialization directly from doubling, are shown to be useful when the layer optical depth is on the order of 10 or less. Finally, questions of round-off error, calculation of an “exact” answer using Richardson extrapolation, and computational efficiency are all addressed briefly.     

折射率正负交替的光子晶体的光学特性研究

介绍了负折射率现象及其优良的光学性能,并从麦克斯韦方程出发推导了正负折射率介质薄层的转移矩阵,经模拟计算发现:正负折射率交替的一维光子晶体有很宽的光子禁带和狭窄的透带,而且无论是TE波还是TM波在中心波长光学特性几乎都不受角度的影响,可用作宽带全方位反射镜,可望在在光路集成、光通信领域得到广泛地应用。     

SU(3) symmetry operational approach to measuring amplitude and phase parameters for an optical field

We consider a new approach to the SU(3) symmetry polarization in Hilbert space for a quantum-optical Bose system with internal Gell-Mann symmetry. The operational determination of the SU(3) amplitude and phase characteristics for a three-mode optical field is discussed for the first time. An original twelve-port interferometer for simultaneous measurements of both the Gell-Mann and the phase parameters is proposed. The quantum properties of various W-class qutrit states under the measurement procedure for quantum information purposes are examined.     

Variational assimilation in combination with a regularization method for sea level pressure retrieval from QuikSCAT scatterometer data II: simulation experiment and actual case study

The sea level pressure field can be computed from sea surface winds retrieved from satellite microwave scatterometer measurements, based on variational assimilation in combination with a regularization method given in part I of this paper. First, the validity of the new method is proved with a simulation experiment. Then, a new processing procedure for the sea level pressure retrieval is built by combining the geostrophic wind, which is computed from the scatterometer 10-meter wind using the University of Washington planetary boundary layer model using this method. Finally, the feasibility of the method is proved using an actual case study.     

Single Telephoto Lens for Focus Error Detection with Astigmatic Method

An astigmatic method for focus error detection has been integrated into a singlet. The first convex and the second concave surfaces compose a telephoto system with a telephoto ratio of about 0.4. The first surface of the lens is rotationally symmetrical asphere and the second surface is a toric shape whose aspherical profiles correct spherical aberration. We implemented our optical design using a molded glass process. Its performance was confirmed using the optical head of a magneto-optical disk system.     

A new approach to the retrieval of surface properties from earthshine measurements

Instruments such as the MODIS and MISR radiometers on EOS AM-1, and POLDER on ADEOS have been deployed for the remote sensing retrieval of surface properties. Typically, retrieval algorithms use linear combinations of semi-empirical bidirectional reflectance distribution function (BRDF) kernels to model surface reflectance. The retrieval proceeds in two steps; first, an atmospheric correction relates surface BRDF to top-of-atmosphere (TOA) reflectances, then regression is used to establish the linear coefficients used in the kernel combination. BRDF kernels may also depend on a number of physical or empirical non-linear parameters (e.g. ocean wind speed for a specular BRDF); such parameters are usually assumed known. A major source of error in this retrieval comes from lack of knowledge of planetary boundary layer (PBL) aerosol properties.In this paper, we present a different approach to surface property retrieval. For the radiative transfer simulations, we use the discrete ordinate LIDORT model, which has the capability to generate simultaneous fields of radiances and weighting functions in a multiply scattering multi-layer atmosphere. Surface-atmosphere coupling due to multiple scattering and reflection effects is treated in full; the use of an atmospheric correction is not required. Further, it is shown that sensitivities of TOA reflectances to both linear and non-linear surface BRDF parameters may be established directly by explicit analytic differentiation of the discrete ordinate radiative transfer equations. Surface properties may thus be retrieved directly and conveniently from satellite measurements using standard non-linear fitting methods. In the fitting for BRDF parameters, lower-boundary aerosol properties can either be retrieved as auxiliary parameters, or they can be regarded as forward model parameter errors. We present examples of simulated radiances and surface/aerosol weighting functions for combinations of multi-angle measurements at several different wavelengths, and we perform some examples of self-consistent non-linear fitting to demonstrate feasibility for this kind of surface property retrieval.     

Accurate density functional calculations of near-edge x-ray and optical absorption spectra of liquid water using nonperiodic boundary conditions: the role of self-interaction and long-range effects

An integrated theoretical approach based on a discrete-continuum solvent model combined with molecular dynamics and time-dependent density functional theory leads to near-edge x-ray and optical absorption spectra of liquid water in excellent agreement with experiments. For quantitative results both self-interaction and long-range effects should be properly corrected. While scaling with respect to a monomer effectively compensates the self-interaction error, long-range effects require inclusion of exact exchange. Further, new physical insights on the not fully elucidated nature of the first optical band are provided.