大气气溶胶粒子折射率虚部反演方法研究

提出了反演折射率虚部的方法.以光散射为原理的粒子计数器测量光学等效直径,其结果受折射率虚部的影响较大;以粒子飞行时间为原理的粒子计数器测量空气动力学直径,其结果不受折射率虚部的影响.利用两种仪器的测量结果受折射率影响的差异来反演大气气溶胶的折射率虚部.通过与其它独立的测量结果对比表明,该方法反演气溶胶折射率虚部是合理的.     

大气气溶胶粒子折射率虚部反演方法研究

提出了反演折射率虚部的方法.以光散射为原理的粒子计数器测量光学等效直径,其结果受折射率虚部的影响较大;以粒子飞行时间为原理的粒子计数器测量空气动力学直径,其结果不受折射率虚部的影响.利用两种仪器的测量结果受折射率影响的差异来反演大气气溶胶的折射率虚部.通过与其它独立的测量结果对比表明,该方法反演气溶胶折射率虚部是合理的.     

OCT图像法测量折射率

基于光程匹配原理提出了一种用光学相干断层成像(OCT)系统获得的图像测量样品折射率的方法。通过分析光程匹配原理,给出用OCT图像法测量样品折射率的原理及过程。以玻璃载波片和黄瓜组织为样品进行实验。实验结果表明,用OCT图像法获得的载玻片和黄瓜组织的折射率测量值分别为1.499和1.353,与发表或已知的折射率结果相吻合,测试结果的随机误差可小于0.01。另外,使用OCT图像法通过短时间所采集的两幅图像可对横向扫描任意位置的折射率同时进行测量。该方法进一步简化了基于光程匹配原理的折射率测量法的过程,缩短了测量时间,是一种快速测量样品折射率的实用方法。     

用掠入射法测量透明介质折射率的探讨

本文介绍了掠入射法测量各种透明介质折射率的实验过程与方法,并用钠光源掠入射法测量乙醇、纯净水和丙三醇的折射率,在实验拓展中对空气、三棱镜的折射率测量进行了探讨。     

用M-Z干涉仪对空气折射率的定量测量与理论探讨

用自行组建的M-Z干涉仪测量空气在不同压强下的折射率,得到恒定温度下折射率随压强变化的具体关系,并从理论上对空气折射率的成因进行了分析,较好地解释了实验结果.     

棱镜耦合法测量负折射率材料光学特性理论研究

对于在光频波段的负折射率介质材料,从理论上提出了测量其光学参量的棱镜耦合法,给出了测量原理、装置,同时给出了棱镜耦合法测量系统的精确理论模型.用转移矩阵方法推导出其满足的色散方程,从理论上分析了空气层厚度对测量结果的影响.用传输矩阵法进行了模拟论证,得到了模拟反射率曲线,同时模拟分析了空气间隙对测量结果的影响.     

圆形双芯微结构色散补偿光纤的色散特性分析

提出了一种圆形双芯微结构光纤,用频域有限差分法(FDFD),并对其色散特性进行了分析,并与前人提出的六边形双芯微结构色散补偿光纤进行了比较。结果表明:当圆形双芯微结构色散补偿光纤的高折射率区半径保持不变时,改变沿水平直径方向相邻空气洞中心点间的距离和空气洞的直径,能够控制有效模折射率的转折点,并在该处产生较大的负色散。由于圆形双芯微结构色散补偿光纤比六边形双芯微结构色散补偿光纤的有效模折射率对参数变化较为敏感,故前者更易于精确地控制转折点,达到色散补偿的目的。     

基于迈克耳孙干涉仪及双空气劈尖测量液体折射率

折射率是介质的一个重要光学参数,对折射率的测量是光学实验中一个重要的组成部分.本实验利用双棱镜和平板玻璃制成的双空气劈尖作为盛放液体的容器,并在迈克耳孙干涉仪上增加了横向传动装置来控制双空气劈尖的移动,设计了一种测量液体折射率的实验装置.该实验方法避免了复杂的元器件加工,操作简便且测量结果较精确.     

用改进的瑞利干涉仪精确测量空气折射率

用激光干涉仪进行精密测长时,需要同时知道准确的空气折射率。由于测量环境的空气成分经常会偏离标准空气成分,使用公式计算空气折射率往往会产生较大的误差。所以在精密的测量中,必须用干涉仪直接测定测量环境的空气折射率。     

测量光纤折射率分布还原算法的研究

用透射式微分干涉法测量光纤内部折射率分布,其原理是利用旋转检偏器对测量光束进行调制,从相位分布和光程分布中计算出折射率分布。其中,从光程分布中解算出折射率分布的算法是关键。讨论了该算法的数学模型,推导了测量公式,并对算法的稳定性和误差进行了分析。利用自行研制的系统对渐变折射率分布光纤进行实测,与在NR 9200光纤测量仪上的结果进行了比较,对主要误差源进行了分析和计算机模拟。实测和模拟计算结果表明,该算法原理正确,系统稳定,测量精度优于10-3,完全可以用来测量光纤折射率分布。     

Terahertz multi-metal-wire hybrid-cladding hollow waveguide for refractive index sensing

We propose a design of terahertz refractive index sensing based on the multi-metal-wire(MMW) hybrid-cladding hollow waveguide. The proposed terahertz hybrid-cladding hollow waveguide comprises one air core in the center surrounding MMW surrounded dielectric. The central air core is used for filling lossless measurands and transmitting terahertz light. In particular, the refractive index sensing is realized by measuring the mode field area(MFA) variation of radially polarized mode. The modal effective refractive index, mode field intensity distribution, and mode field area properties responding to the measurand refractive indexes for different operating frequencies and structure dimensions are investigated, respectively.Simulations show that the proposed terahertz refractive index sensor can realize easily the measurement of the measurand refractive index. Meanwhile, the effects of operating frequency and structure parameters on sensitivity and measurement accuracy are also studied. In view of the trade-off between sensitivity and measurement accuracy, the reasonable choice of the operating frequency and structure parameters can optimize appropriately the sensitivity and measurement accuracy, and the sensitivity can reach approximately 0.585 mm~2/RIU(RIU is short for refraction index units) with the proper frequency and structure parameter.     

Direct measurement of the complex refractive index of thin foils in the XUV spectral range by point diffraction interferometry

In this paper, we demonstrate the application of point diffraction interferometry to determine the complex refractive index of thin foils in the extreme ultraviolet spectral range. Results are cross-checked by an independent interferometric measurement of the refractive index and a direct transmission measurement of the foils. As the light source, we apply high-order harmonics of a titanium-sapphire laser generated in a gas jet. This interferometric method has the advantage to simultaneously and directly deliver the refractive and absorptive part of the refractive index without relying on the Kramers–Kronig relations or the Fresnel equations. We present results for a set of materials (aluminum, silicon, germanium, boron, and parylene), which are of interest for the design of bandpass filters or multilayer coatings.     

Accurate measurement of the refractive index of CO2, N2, He, O2, and air at 10.57 μ and T = 23 °C

The refractive index of carbon-dioxide, nitrogen, helium, oxygen and air have been measured at 23 °C temperature by means of a tunable CO₂ laser at 10.57 μm and of a differential interferometric technique. As the gas refractive index depends on the pressure P as n = 1 + _PP, the pressure coefficients _P has been measured with 5e–3 accuracy.     

“干涉逼近法”测量液体折射率

提出了一种高精度测量液体折射率的新方法一“干涉逼近法”.这种方法可以在测量过程中监视被测液体温度不均匀性给测量带来的误差.由于受温度测量的限制,其测量液体折射率的不确定度在1×10~(-6)到4×10~(-5)(2σ)之间,具体值取决于液体折射率的温度系数.     

Tomographic reconstruction of sound fields in air using TV-holography

A vibrating sound source causes periodic pressure variations in the air. The pressure variations lead to corresponding variations in the refractive index of the air which can be measured using full field interferometric techniques like TV-holography. Each measurement maps a cross-section of the integrated sound fields. To obtain a complete map of the volume distribution of sound field, we record cross-sections from different directions. Using tomographical backprojection of these recordings, we reconstruct the amplitude and phase of the sound field in any plane of the volume.     

Optical diffraction tomography microscopy with transport of intensity equation using a light-emitting diode array

Optical diffraction tomography (ODT) is an effective label-free technique for quantitatively refractive index imaging, which enables long-term monitoring of the internal three-dimensional (3D) structures and molecular composition of biological cells with minimal perturbation. However, existing optical tomographic methods generally rely on interferometric configuration for phase measurement and sophisticated mechanical systems for sample rotation or beam scanning. Thereby, the measurement is suspect to phase error coming from the coherent speckle, environmental vibrations, and mechanical error during data acquisition process. To overcome these limitations, we present a new ODT technique based on non-interferometric phase retrieval and programmable illumination emitting from a light-emitting diode (LED) array. The experimental system is built based on a traditional bright field microscope, with the light source replaced by a programmable LED array, which provides angle-variable quasi-monochromatic illumination with an angular coverage of ±37 degrees in both x and y directions (corresponding to an illumination numerical aperture of ∼0.6). Transport of intensity equation (TIE) is utilized to recover the phase at different illumination angles, and the refractive index distribution is reconstructed based on the ODT framework under first Rytov approximation. The missing-cone problem in ODT is addressed by using the iterative non-negative constraint algorithm, and the misalignment of the LED array is further numerically corrected to improve the accuracy of refractive index quantification. Experiments on polystyrene beads and thick biological specimens show that the proposed approach allows accurate refractive index reconstruction while greatly reduced the system complexity and environmental sensitivity compared to conventional interferometric ODT approaches.     

A review on refractive index and temperature profile measurements using laser-based interferometric techniques

In this review we have discussed laser-based interferometric techniques for measurement of refractive index, temperature and temperature profile of burners with special emphasis on laser speckle techniques and Talbot interferometric technique.     

Group refractive index measurement by fringes of equal chromatic order

Fringes of equal chromatic order in transmission across a thin liquid or a thin solid sample inside a wedge interferometer, followed with a grating spectrograph, are produced. A single-shot interferogram of the air and sample regions is recorded. Locations of fringes maxima in the air region are fitted in a numerical procedure based on Cauchy's dispersion function. Then it is used for measuring the interferometric gap thickness. The order of interference in the sample region is represented by a third-order polynomial in the wavenumber for deducing the sample group refractive index. An error analysis of the measured group refractive index is given. The method is applied for measuring the group refractive index of water and mica samples across the visible spectrum. The method measures both the sample thickness and its group refractive index. It is static with no moving parts and suitable for thin liquid or solid samples without immersion liquids.     

Determining the refractive index of liquids using a modified Michelson interferometer

An accurate method for measuring the refractive index of liquids is proposed, modeled, and experimentally verified. The experimental setup is a modified Michelson interferometer employing a novel liquid chamber that allows the optical pathlength to be continuously varied without moving a mirror. This experiment allows determining the refractive index of a given liquid to high precision, with an accuracy limited only by the normal random variables encountered in interferometric measurements and ultimately the accuracy to which the wavelength of the laser light is known.     

高精度V棱镜折射仪光机结构设计

针对传统V棱镜折射仪采用光学度盘,目视对准方式无法满足现代光学玻璃生产线以及高精度折射率测量的需求。提出一种新型的高精度基于CCD 机器视觉对准的V棱镜折射仪的总体设计方案,并对准直光管、传动机构、锁紧和微调机构以及轴角编码测角机构等主要组成部分进行了光机结构设计。在考虑空气折射率影响因素的修正公式的基础上,分析了仪器的检测误差。实验结果表明:其折射率检测精度可达 310-6,满足了高精度V棱镜折射仪的技术指标要求。