真空腔测量空气折射率的方法及精度分析

空气折射率的测量及补偿效果在高精度激光干涉测量中起着“瓶颈”作用。分析了空气折射率的补偿原理 ,研究了用预抽气真空腔测量和补偿空气折射率的测量原理、方法及装置 ,分析了该方法对测量误差产生的原因。最后对测量精度作出了估计。     

Optical coherence refractometry

We introduce a novel approach to refractometry using a low coherence interferometer at multiple angles of incidence. We show that for plane parallel samples it is possible to measure their phase refractive index rather than the group index that is usually measured by interferometric methods. This is a significant development because it enables bulk refractive index measurement of scattering and soft samples, not relying on surface measurements that can be prone to error. Our technique is also noncontact and compatible with in situ refractive index measurements. Here, we demonstrate this new technique on a pure silica test piece and a highly scattering resin slab, comparing the results with standard critical angle refractometry.     

基于吸收光谱和激光干涉技术的气体压力测量方法研究

气体压力光学非接触测量是目前激光技术重要应用领域之一,其中气压测量过程中温度耦合问题是现在面临的研究难点。故而提出一种光谱测量技术与激光干涉技术组合测量方法,通过积分吸光度和折射率融合的方式实现气体压力、温度解耦的目的。分析可调谐半导体激光光谱技术(TDLAS)的直接吸收法测量原理和基于折射率的激光干涉测量原理,建立基于吸收光谱的气压测量模型和基于折射率的激光干涉气压测量模型,通过利用三次多项式拟合吸收谱线强度函数的方式,建立了基于积分吸光度和折射率的气体压力、温度解耦的数学模型。实验搭建了基于TDLAS技术和激光干涉技术的气体压力检测系统,采用中心波长为2 004 nm的可调谐半导体激光器和波长为632.8 nm的激光干涉仪,气室长度为24.8 cm,将CO₂作为研究对象,并以高精度压力控制器和温度传感器的测量结果分别作为压力温度参考值,以真空为背景信号,在室温环境中测量并计算出气体压力变化后积分吸光度值和折射率值,进而解算得到气体压力和温度值。实验结果显示：压力测量结果最大相对误差为3.61%,最小相对误差为0.5%,测量平均相对误差为1.99%;在以开尔文温度为前提下,温度解算结果最大绝对误差为7.66 K,最小绝对误差为0.78 K,测量平均绝对误差为3.29 K,测量结果与参考结果具有较高的吻合度,该研究可为以后光学法测量气体压力温度影响分析提供参考。     

紫外LED圆环阵列均匀照明的实现方法

为构造指纹荧光检测中所需的均匀照明紫外光源,选择紫外LED阵列照明。采用光电探测器检测单颗LED的辐射角分布,拟合单个LED角分布函数;用8颗LED均匀置于半径为10 mm的圆环上,在圆环上方5 mm处的中心轴上放置一个LED;在给定的观察屏上照度不均匀误差下,根据斯派罗法则,确定观测屏与圆环阵列之间的距离,从而实现LED圆环阵列的照度分布均匀化。也可以给定观测屏到圆环的距离,确定轴上LED放置点到圆环的距离。实验结果表明,观测屏到圆环距离为11.0 cm时,在半径为10.0 mm的圆域内,照度不均匀相对误差小于1.27%。     

彩色视觉装置的颜色校正对比实验研究

鉴于利用彩色视觉装置进行在线测量是颜色测量在工业应用发展的趋势,而光源的光谱分布和相机响应函数与人眼的光谱响应曲线的不一致会严重影响测量的精确性,在人工D65光源和LED阵列光源照明下,利用相同的工业相机获取校正图片,采用多项式回归方法在与设备无关空间sRGB和CIEL*a*b*空间进行校正。实验结果显示在校正前平均色差分别为27.68E和16.09E,人工D65光源照明下获取的图片色差较小,校正后不同光源下获取图片的色度趋于一致,分别为2.56E和2.39E。采用sRGB颜色空间,在校正精度、校正步骤、图片显示等方面都要优于CIEL*a*b*空间。以一幅拍摄的实际图片校正为例,显示了色度校正对彩色装置的重要性。     

Surface profilometry based on polarization analysis

We report a novel algorithm for the analysis of interferometric images for surface profiling. The algorithm can be used with any interferometric system in which the two interfering beams are orthogonally polarized. The algorithm is based on a measurement of the polarization state and gives a unique value for the path difference that is not subject to the ambiguities associated with fringe counting or phase unwrapping. A detector array allows the polarization state and hence the height of every pixel in the image to be determined simultaneously. The concept is easily extended to enable one to obtain the profiles of moving surfaces from a single pulse of illumination.     

Coherent beam combination of 137 W fiber amplifier array using single frequency dithering technique

We demonstrate coherent beam combination of 137 W fiber amplifier array using single frequency dithering technique. Four polarization-maintained fiber amplifiers are tiled into 2×2 array and the output power of each amplifier is about 35 W. Single frequency dithering algorithm is run on a signal processor based on field programmable gate array (FPGA) for phase control on the fiber amplifiers. When the phase control system goes into closed-loop, the fringe contrast of far-field intensity pattern is improved by more than 87% from 0 in open-loop, and the residual phase error is less than λ/20.     

Particle Imaging Using a Transmission Wide‐Field Phase Confocal Microscope

A phase‐sensitive wide field transmission microscope, combining the advantages of both interferometric and confocal techniques, has been developed and applied to analysis of particulates, both in dry powder form and in suspensions. The microscope has also been used in detecting defects in crystals. Confocal operation is achieved by superimposing speckle illumination of a reference beam in a Mach‐Zehnder interferometer with a matched speckle pattern of the object beam. It is shown that the phase measurement enables particle size to be determined even when the particle is smaller than the focal spot size. The data acquisition time is below 1ms, making the system suitable for dynamic process measurement. The experimental results are in good agreement with modelled results giving rise to the possibility of simultaneous determination of both the size and refractive index of small particles.     

A refractive index interferometry method based on the X-ray crystallography

The absorption contrast image is very low for those weakly absorbing materials or weak phase object, such as the soft biological tissues, however, the phase item value of refractive index is a thousand larger than the absorption item, therefore the refractive index interferometry method is expected to be a new imaging tool for them. An interferometry method based on the X-ray crystallography is explored to the measurement of refractive index in this paper. The theoretical foundation, the optical design, the crystal transistor performance are the key parts to this interferometry method based on the X-ray crystallography. We give out a special refractive index detection scheme, using a laboratory hard X-ray source, and four single Si crystals. With this instrument, refractive index profile of those weak phase object can be unfolded accurately using this method. This refractive index interferometry method based on the X-ray crystallography will provide a new research tool for those special material properties or biological tissues study.     

平面LED阵列远场条件研究与实验验证

平面LED(light-emitting diode)阵列远场条件是实现其光度学参数正确测量的前提,为了确定不同平面LED阵列的远场条件,基于点光源发光强度的测量原理建立了面光源光轴上的不同距离下照度与距离平方乘积的函数关系模型,用其表征面光源光轴上光场的分布规律.在此基础上利用照度平方反比定律,以及平面LED阵列远场...     

Comparative study between interferometric and Z-scan techniques for thermal lensing characterization

This work presents an original, comparative study between two optical techniques for the analysis of thermal lensing induced by a low-power, cw laser beam focused onto a sample cell containing a weak absorbing medium. It deals with an interferometric technique and a Z-scan technique in real time. The interferometric method permits the determination of the spatial profile of the thermal lens. The development of the work puts in evidence the high sensitivity of both techniques for the detection and measurement of low absorption coefficients and refractive index changes in dye solutions at very low concentrations. Improvements in the sensitivity of both methods can make possible the measurement of very small phase shift distortions of the wavefront. One shows also the mutual complementary character of two techniques for the characterization and measurement of linear and nonlinear properties of materials.     

Measurement of air refractive index based on surface plasmon resonance and phase detection

A method for refractive index of air measurement is presented based on surface plasmon resonance (SPR) and phase detection using a dual-frequency laser interferometer. Theoretical analyses indicate that the phase-difference variation of the measurement signal versus the reference signal is linear with refractive index of air (RIA) fluctuation, and the calculation formula of RIA is derived. The structure design of the self-adaptive SPR sensor greatly reduces the measurement error resulting from the incident angle shift and improves the sensitivity. The experiments show that measurement uncertainty of 10(-6) order has been achieved when phase detection precision is 0.1°. The phenomenon of sudden phase variation during air pumping and air filling, which is caused by temperature fluctuation, is discussed.     

光纤干涉成像阵列全息相位校正研究

针对光纤传输和干涉成像阵列中的相位误差, 提出了一种基于特殊光子晶体的全息相位校正方法。首先分析了光纤干涉阵列成像的基本原理和相位信息的传输过程, 以一维线性阵列建立成像系统相位误差模型, 通过对参考光束和探测器前的快门交替打开和闭合, 来分别实现在晶体上写入由光纤阵列的出射光束与参考光束干涉形成的含有相位误差的光栅函数, 和光纤中出射光束被该光栅衍射和相位偏移以消除相位误差, 从理论上分析了上述基于光子晶体的全息法相位校正原理。最后采用所建立的含有相位误差的干涉阵列进行成像仿真, 对未加校正、采用本文方法和采用冗余基线校正的结果进行了对比分析。     

干涉型表面等离激元显微术成像的研究

运用Matlab系统地模拟了信号光相位与样品的厚度和折射率之间的对应关系,为干涉型表面等离激元显微术提供了理论依据,同时证明了基于相位探测的干涉型表面等离激元显微术相比基于强度探测的表面等离激元显微术具有更高的纵向分辨率,而且为生物化学方面的动态变换过程的实时监测提供了一种新方法.     

Measurement of small differences in refractive indices of solutions with interferometric optical method

Based on the principles of both surface plasmon resonance (SPR) and heterodyne interferometry, an optical method for measuring small differences in refractive indices of solutions was proposed. On a specially designed probe, two light beams are incident on both reference and test solutions. The phase differences between the p- and s-polarizations of each reflected light under SPR condition are measured simultaneously with heterodyne interferometric technique. The phase values are substituted into special equations derived from Fresnel's equations. Finally, the difference between the refractive indices of these two solutions can be estimated. The feasibility of this method was demonstrated and the measurement sensitivity of refractive index can reach a value of at least 8.57×10⁻⁷. This method should bear the merits of a simple structure, easy operation, high sensitivity and rapid measurement.     

基于近场均匀照明的LED阵列的优化设计

基于几何光学与辐射照度理论,对菱形、环形和蜂窝状等3种典型LED阵列光源在近场上的照度分布进行研究,推导了不同阵列光源照射到目标面上的总辐射照度表达式,并依据斯派罗法则确定了LED间的最优化距离。进而根据照度公式,对LED阵列进行了仿真和对比分析,得出了不同阵列的光照度分布特点。菱形阵列可以得到较大范围的平坦度,环形阵列的平坦范围较小,能量集中分布在一个圆形范围内,有良好的集光效果,蜂窝状阵列的照度比较集中且占用的面板空间较小,可在一定程度上降低设计成本。     

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.     

厚度误差对THz-TDS的测量不确定度分析

阐述了基于菲涅尔公式的透射式太赫兹时域光谱系统提取样品光学常数的方法和原理,分析了样品厚度误差对THz-TDS测量不确定度的影响,并建立了相应的不确定度模型。进行太赫兹时域光谱测量实验,提取硅片在太赫兹波段的折射率,并计算了误差对提取样品折射率的影响。结果表明,随着厚度误差的增大,系统测量偏差也随之增大。对于较厚样品,相同厚度误差对其测量结果影响较小。样品厚度为994μm时,在厚度存在1μm的测量误差情况下,系统测量折射率的偏差为0.001 2,接近模型的仿真值。实验结果验证了厚度误差对测量不确定度模型的有效性,了解了厚度误差对系统测量结果的影响情况,对测量过程及结果分析具有一定的指导意义。     

高折射玻璃微珠粒径与折射率关系的研究

利用激光照射高折射率玻璃微珠下形成的二次彩虹现象,以艾里的虹理论为基础对玻璃微珠折射率进行了测量。推导了玻璃微珠尺寸对折射率影响的计算公式,表明半径差异在10μm时,折射率的测量误差为10^-3数量级。此外,通过软件模拟计算玻璃微珠的二次彩虹现象,并对微珠的折射率进行了测量,验证了二次彩虹方法的正确性,同时也表明玻璃微...     

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.