基于低相干光干涉的液体折射率测量

液体折射率是液体一个重要指标,介质中折射率的变化会影响光程,提出一种用低相干光干涉测量光程变化,进而测得折射率的方法。通过调节两束低相干光使它们之间的光程差在相干长度之内,将被测液体放入一束光路中,根据光电探测器得到的干涉信号可求得相应的光程变化量,进而得到待测液体的折射率。利用低相干光干涉测量折射率的方法,其测量和计算过程方便快捷,受外界限制因素小,在810nm波长下,对折射率的测量精度可以达到10-4量级以上,是测量各种液体折射率的有效方法。     

基于负折射率声透镜的亚波长分辨率光声实时成像方法

基于负折射率材料的信号处理技术为光声图像的研究提供了新的思路。光声成像是一种全新的非破坏性生物光子技术,是一种基于生物组织内光吸收差异的成像方法。然而,当前的光声成像方法主要依靠传感器扫描工作,而传感器阵列有其固有的缺点,导致实时性较差,因此,普通的光声成像方式具有一定的局限性。但是,利用具有负折射率的声透镜特性(如聚焦、滤波、定向等)构成的成像方式可以解决普通光声成像中的这些局限性问题。本文在对负折射率声透镜的负质量响应和负折射率成像进行优势分析后,提出了利用声透镜改变当前扫描成像的方法。模拟分析实验结果表明,所设计的声透镜直接成像方案达到了预期效果,透镜成像后像点的声压分布与吸收体原始的声压分布基本一致。此外,0.6倍波长的实验图像结果说明本文实现了亚波长的光声成像效果。     

光通信用自聚焦透镜的制备

制备了自聚焦透镜的基础玻璃,对其透过率进行了测试,并对由这种玻璃制成的梯度折射率(GRIN)棒的折射率分布进行了分析.结果表明,基础玻璃在可见和近红外波段的透过率大于89%;GRIN棒内部的折射率分布接近理想分布.     

折射率失配对双光子三维信息存储中信息点的影响

根据Torok的光在多层介质中传播的理论,模拟了在折射率失配情况下点扩展函数的强度分布.在介质折射率为1.48,多种物镜数值孔径NA=0.25、0.45、0.65、0.85条件下,分析了信息点轴向尺寸及读出信号强度变化趋势.选取合适的光学参数(如物镜的数值孔径NA=0.45,存储介质的折射率1.48),能够使信息点在深度200μm内轴向尺寸变化率小于4%,信号读出强度变化率小于30%,提高了存储效果.对选取各种物镜和介质折射率的情况下信息点的变化趋势分析表明,折射率失配使信息点横向尺寸随深度变化不大,而轴向尺寸及信号读出强度产生较大的变化,变化的程度与物镜NA、介质的折射率及存储深度密切相关.采用与模拟时相同的光学参数,在光致变色材料中进行了双光子三维存储实验.通过观察信息点的轴向及横向扫描图像和信号的读出强度,证实了这种变化趋势.实验结果为双光子三维存储提供了参考依据.     

Three-dimensional refractive index reconstruction with quantitative phase tomography

Optical tomography based on quantitative phase microscopy is used to determine nondestructively and with high spatial resolution the three-dimensional (3D) refractive index distributions within optical fiber devices. After obtaining a series of phase images of the fiber as it is rotated around its longitudinal axis at regularly-spaced angular positions, filtered backprojection is used to reconstruct a 3D map of the refractive index. The 3D refractive index distribution of the join region between two fusion spliced optical fibers is reconstructed with accuracy better than 10(-3).     

Nonray‐tracing determination of the 3D refractive index profile of polymeric fibres using single‐frame computed tomography and digital holographic interferometric technique

In this paper, we present a nonray‐tracing technique for evaluating the three dimensional distribution of the refractive index values inside polymeric fibres. This technique, named ‘single‐frame computed‐tomography (SFCT)’, is applied to digital holography. A comparative study between the calculated optical phase values using ordinary tomography and SFCT is carried out, and a negligible deviation is detected. The proposed technique is used to determine the three‐dimensional refractive index profile of isotactic Polypropylene fibres, IPP. The variation of the optical properties is measured before, during and after the formation of the necking phenomenon. In addition, SFCT technique is applied to the online determination of the change of the optical properties of IPP fibres. Holograms are given for illustration.     

基于光纤激光频率分裂效应的折射率 / 厚度 双参量测量研究

折射率作为光学系统中应用最广泛的光学参数之一,对系统的光学性能具有极其重要的影响。 厚度与折射率所组成的 光学长度直接影响双折射器件在光学系统中的时延特性。 本文提出一种基于光纤激光频率分裂效应的折射率/ 厚度双参量测 量方法。 该系统通过对插入激光腔内的双折射器件进行旋转,利用频率分裂效应对不同角度的器件的双折射参数进行测量。 基于双折射器件中的折射率椭球,建立相位延迟、折射率、厚度和旋转角度之间的关系,通过拟合计算得到器件的折射率/ 厚度 参数。 实验结果表明,通过该系统对双折射元件的厚度测量误差为 210 nm,本征折射率进行测量误差为 10 -5 ,可广泛应用于红 外波段的双折射器件的本征折射率/ 厚度双参量测量。     

透明毛细管管壁折射率的无损测量

介绍了一种无损测量透明毛细管管壁折射率的方法。该方法利用平行光经过装有不同已知折射率标准液体的毛细管后会聚焦点位置不同的原理,通过CCD对会聚焦点位置成像后的图像进行判断,计算出毛细管外轮廓位置和焦距,进而计算出毛细管管壁的折射率,其测量精度可达0.005。分析了毛细管内外径对管壁折射率测量的影响,结果表明,管壁越厚,测量精度越高;同时对毛细管管壁折射率灵敏度和成像系统的景深值进行了计算和比较,结果显示,标准液体折射率越低,标定精度越高。该方法使用设备简单,操作方便,便于对图像观察和识别,实现了对毛细管管壁折射率的无损精确测量。     

一种精确测量微量液体折射率的新方法

摘 要：本文介绍了一种用玻璃毛细管精确测量微量液体折射率的新方法。这种方法基于共轴球面光学系统的成像原理,通过读数显微镜对吸入待测液体后毛细管的焦点位置进行单一参数的测量,进而计算出待测液体的折射率。用此方法测量了纯水、乙醇、乙二醇、丙三醇的折射率,各种待测样品的需要量小于0.002 ml;对纯水和乙醇样品,折射率测量精度优于0.0003;对乙二醇和丙三醇样品,折射率测量精度优于0.0007。选用适当的毛细管参数,可以进一步提高这种测量方法的测量精度,扩展折射率的测量范围。该方法具有待测液体用量极少、使用的设备简单、操作方便和折射率测量精度高的特点。论文对实验测量误差以及进一步提高测量精度作了详细的分析和讨论。     

Interferometric technique for measuring the refractive index variation of a liquid with temperature

A technique for measuring the variation of refractive index of a liquid as a function of temperature or solute concentration using a Mach-Zender interferometer is described. The principal difficulty of obtaining a uniform temperature along the optical path in the sample liquid while simultaneously varying the temperature at a reasonable rate is overcome by heating the liquid in a separate vessel and injecting the heated fluid into the test vessel as a series of jets to encourage turbulent mixing. An equivalent resolution in the refractive index variation of 2x10(-6) was obtained. The above method was used to determine the variation of refractive index in a 0.1% NaCl/H(2)O solution in the temperature range 23 degrees -33 degrees C.     

毛细管成像法精确测量微量液体的折射率

介绍了一种用玻璃毛细管成像法精确测量微量液体折射率的方法及测量装置.该方法以充人透明液体的毛细管构成柱透镜,基于共轴球面光学系统的成像原理,对光学成像系统的放大率进行单一参数的测量,进而计算出待测液体的折射率.测量了纯水、乙醇、乙二醇、丙三醇的折射率,各种待测样品的需要量均小于0.002 mL,结果显示本试验装置的测量准确度与目前商用阿贝折射仪(±0.000 2)相当.另外,测量了不同浓度的乙二醇水溶液的折射率,并对测量的数据点进行了曲线拟合,测试结果与阿贝折射仪测量结果和理论公式计算结果所拟合曲线吻合完好.该方法具有待测液体用量极少、操作方便和折射率测量精度高的特点,适用于微量液体折射率的精确、快速测量.     

Time-resolved imaging of laser-induced refractive index changes in transparent media

We describe a method to visualize ultrafast laser-induced refractive index changes in transparent materials with a 310 fs impulse response and a submicrometer spatial resolution. The temporal profile of the laser excitation sequence can be arbitrarily set on the subpicosecond and picosecond time scales with a pulse shaping unit, allowing for complex laser excitation. Time-resolved phase contrast microscopy reveals the real part of the refractive index change and complementary time-resolved optical transmission microscopy measurements give access to the imaginary part of the refractive index in the irradiated region. A femtosecond laser source probes the complex refractive index changes from the excitation time up to 1 ns, and a frequency-doubled Nd:YAG laser emitting 1 ns duration pulses is employed for collecting data at longer time delays, when the evolution is slow. We demonstrate the performance of our setup by studying the energy relaxation in a fused silica sample after irradiation with a double pulse sequence. The excitation pulses are separated by 3 ps. Our results show two dimensional refractive index maps at different times from 200 fs to 100 μs after the laser excitation. On the subpicosecond time scale we have access to the spatial characteristics of the energy deposition into the sample. At longer times (800 ps), time-resolved phase contrast microscopy shows the appearance of a strong compression wave emitted from the excited region. On the microsecond time scale, we observe energy transfer outside the irradiated region.     

角度位置自动识别的红外折射率测量

为准确快速获得块体硫系玻璃红外波段的折射率,搭建了基于类准直测量法的折射率测量系统。该系统采用液氮制冷的碲镉汞探测器和特殊的光路实现了光强信息的高分辨采集,使用高分辨数据采集卡将角度信息数字化,利用精密步进电机传动控制系统实现了光强信号与位置信号的同步记录。开发的测量软件可自动判别光强峰位信息,自动计算获得待测样品的折射率。对比测试Ge_(20)Sb_(15)Se_(65)、Ge_(28)Sb_(12)Se_(60)、As_2S_3和As_2Se_3商用硫系玻璃在3.39μm和4.8μm处的折射率。实验结果表明,该装置系统测量折射率的标准偏差为10~(-3),测量不确定度为0.002 9,可快速、准确测量块体材料红外波段的折射率。     

食用油品质的光学低相干外差干涉检测法

液体的折射率是一个重要的物理参数,在外界一定的条件下,掌握液体折射率及其变化,则可以了解其纯度、浓度等参数及品质。提出一种用低相干光外差干涉方法测量反复使用食用油的折射率,进而鉴别油的品质。实验以改进的迈克尔逊干涉仪为基础,将样品油放入测量臂光路中,当两束分别来自测量臂与参考臂的低相干光的光程接近相等时,会出现光外差干涉现象。利用光电探测器得到此干涉信号,根据前后相应的光程变化量,进而得到待测样品的折射率。食用油经反复加热1、2、3、5、7次后,葵花油的折射率分别为1.469 5、1.469 7、1.470 1、1.470 7、1.471 3,玉米油的折射率分别为1.468 8、1.469 1、1.469 4、1.470 1、1.471 1。结果表明,该方法可以准确测量出不同加热次数食用油的不同折射率,测量稳定性较高,能快捷、有效地鉴别反复使用的食用油品质。     

测量自聚焦光纤透镜聚焦常数的曲线拟合算法

提出了基于曲线拟合的光纤透镜聚焦常数的测试方法,用于超小自聚焦光纤探头研制过程中聚焦常数的直接测试。基于自聚焦光纤透镜模型及其折射率分布特征,研究了测量自聚焦光纤透镜聚焦常数的二次多项式拟合和线性化拟合算法。论述了聚焦常数对超小自聚焦光纤探针传光性能的影响。利用光纤端面折射率测试仪测试自聚焦光纤的折射率分布轮廓曲线,根据二次多项式拟合和线性化拟合算法分别求得聚焦常数和中心折射率。实验结果显示,利用二次多项式拟合算法和线性拟合算法求出的聚焦常数分别为5.587mm-1和5.513mm-1,与厂家的标称值5.5mm-1基本吻合,表明曲线拟合算法适用于对自聚焦光纤透镜聚焦常数的测量与分析。     

聚焦法测量梯度透镜剖面折射率分布的讨论

聚焦法能较好地用梯度透镜剖面折射率分布的测量中是一种装置简单测量迅速的测试方法.     

Measuring the refractive index in a wave excited in water by a laser pulse

The problem of measuring the refractive index in a spherical wave using the Toepler method with a two-sectional photodetector is considered. A technique for determining the width and amplitude of a wave perturbation from the measured time dependence of a schlieren signal is presented. It is shown experimentally that when a water surface is irradiated with an HF-laser pulse (the pulse energy is 50 mJ, the duration is 60 ns), an elastic wave with a width of ~2 mm and an amplitude that is inversely proportional to the travelled distance is excited. The minimum recorded value of the refractive-index gradient is ~3 × 10–8 mm–1; the absolute measurement error of the refractive index is 1.5 × 10–8. The obtained sensitivity and accuracy exceed the results that were previously published. The proposed approach is characterized by the extreme simplicity of the equipment, as well as by the easiness of the experimental implementation and processing of the measurement results.     

Measurement error in prism coupling method and refractive index profile reconstruction in ion-exchanged waveguides

Measurement error in prism coupling method is studied and an analytic expression for the uncertainty of mode effective index measurement in an ion exchanged surface waveguide is derived. A novel algorithm to determine the profile of refractive index for ion-exchange waveguides is proposed. This method takes the values calculated by anti-WKB and linear segment interpolation as approximation and then uses the least squares fitting to eliminate the measurement error. Numerical results show that the proposed algorithm can effectively reconstruct the transverse refractive index profile of graded ion-exchange planar waveguides.     

A procedure to determine the correct thickness of an object with confocal microscopy in case of refractive index mismatch

A difference in refractive index (n) between immersion medium and specimen results in increasing loss of intensity and resolution with increasing focal depth and in an incorrect axial scaling in images of a confocal microscope. Axial thickness measurements of an object on such images are therefore not exact. The present paper describes a simple procedure to determine the correct axial thickness of an object with confocal fluorescence microscopy. We study this procedure for a specimen that has a higher refractive index than the immersion medium and with a thickness up to 100 µm. The measuring method was experimentally tested by comparing the thickness of polymer layers measured on axial images of a confocal microscope in case of a water–polymer mismatch to reference values obtained from an independent technique, i.e. scanning electron microscopy. The case when the specimen has a lower refractive index than the immersion medium is also shown by way of illustration. Measured thickness data of a water layer and an oil layer with the same actual thickness were obtained using an oil-immersion objective lens with confocal microscopy. Good agreement between theory and experiment was found in both cases, consolidating our method.