Measurement of aerosol absorption using photothermal low coherence interferometry

研究了气溶胶粒子的光热敏效应和热感应光致折射率变化,提出了通过增加光热作用区个数来提高探测灵敏度及用低相干干涉法降低成本的方法.建立了光热低相干干涉法测量大气气溶胶吸收系数的数学模型,分析了干涉仪正交状态测量和干涉条纹细分探测两种方式下的探测灵敏度,讨论了低相干偏振干涉情况下的探测限.结果显示,在典型条纹细分情况下理论探测灵敏度可达1×10-6m-1;增加光热作用区m个,探测灵敏度理论值可提高m倍.理论和方法研究证明光热低相干干涉法具有可直接测量大气气溶胶吸收系数、在线原位、低成本,易于进行温度修正等优点.     

应用于眼轴参数测量的光学相干层析系统

生物测量在眼科疾病的诊断和治疗中越来越重要,对儿童和青少年的眼轴长度进行监测有助于预防和治疗近视及其引发的眼科疾病,眼轴参数的准确测量也是影响眼病患者术后视觉质量的重要因素。为了测量眼轴参数,本文研究了基于时域低相干技术的眼轴测量方法,研制了高精度、非接触式眼轴测量的原理样机,并开展了相应的实验研究。利用低相干干涉技术与长相干干涉测距技术结合的方法,采用时域的机械扫描方式,搭建一套光纤型低相干层析测量系统。通过对标准透镜厚度和镜面间隔的测量实验,重复测量精度优于0.3μm。最后对鱼眼眼轴参数进行测量,清晰得到鱼眼的角膜、晶状体和视网膜等结构。实验结果表明,该系统的稳定性及重复性均能达到设计要求,可以用于动物眼轴参数的测量。     

CFBG色散特性低相干干涉测量的误差分析

CFBG(Chirped Fiber Bragg Grating)是一种光纤无源器件,在光通信系统的色散补偿以及传感技术等方面具有广阔的应用前景,其色散特性对其推广应用具有至关重要的作用。本文介绍一种CFBG色散特性测量的光纤低相干干涉系统,并说明其测量原理。进行了相关的实测实验并对所采集的干涉图进行数据处理。实验表明该系统测量精度高,达到皮秒(群时延)量级,并且测量速度快。并对系统进行了误差分析。     

基于逆向蒙特卡洛法的溶液葡萄糖浓度低相干测量

提出了基于蒙特卡洛逆运算的葡萄糖含量低相干干涉测量方法,理论研究了葡萄糖含量与光学参数的相关性.通过正向蒙特卡洛数值模拟说明了从干涉曲线中同时求解散射系数和吸收系数的条件和可行性.以脂肪乳悬混溶液Intralipid作为实验对象,研究了糖浓度变化对深度相关干涉信号的影响.利用低相干干涉测量系统配合逆向蒙特卡洛计算提取了散射和吸收系数,进而通过散射和吸收系数的变化量间接获得了溶液葡萄糖含量.对实验结果与双积分球测量结果进行了比较验证,并对存在的系统误差进行了修正.实验结果显示,在加入修正值后,测量的散射和吸收系数的最大相对误差分别为2.52％和3.11％.研究结果表明,葡萄糖含量与散射系数和干涉曲线存在高度相关性,在非前向散射条件下,可以同时测量吸收和散射系数.经过校准后的测量结果满足了实际要求.     

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。     

基于低相干光干涉原理的眼轴测量研究

眼轴长度测量的精确度对近视防控及白内障患者术后视力恢复治疗等具有重要意义。本文介绍一种非接触光学测量技术,利用低相干光干涉原理研究相比传统测量及其他光学测量的新的系统,通过两路回光产生的干涉,达到无接触、精度更高的测量,达到20μm的误差,并进行模拟眼重复性测试,与现有IOL Master进行多组数据对比,验证其良好的准确性与精确度。     

光干涉法显微镜测量三维表面形貌研究

本文介绍了利用光干涉法显微镜测量三维表面形貌.利用计算机对在光干涉法显微镜下拍摄的零件表面轮廓条纹图象进行图象识别与处理,自动寻找条纹和计算,直接获得三维表面轮廓形貌.测量结果与触针式轮廓仪的测量结果进行了比较.     

圆锥量规锥度的高精度光学干涉法测量

针对超精密数控机床对圆锥量规锥度高精度测量的需求,研究了一种将“大数”和“小数”相结合,准确测量圆锥量规锥度的方法.介绍了锥度测量系统的基本原理及组成,给出了实验测量结果,分析了测量系统的不确定度.该测量方法利用最大分度间隔误差为0.10〞的多齿分度台构成高准确度分度系统保证测量“大数”部分的准确性,采用激光偏振干涉装...     

干涉法表面形貌测量使用的扩展深度测量范围的方法

系统归纳了在干涉法表面形貌测量中使用的用来扩展深度测量范围的各种方法,分析了这些方法的原理、特性及性能指标,比较了这些方法的优越性。     

双孔载频剪切散斑干涉法测量表面动态形变

为了精确地测量物体表面的动态形变并得到形变高度和梯度信息,提出了一种基于双孔衍射结构的空间载频剪切散斑干涉法.该方法采用双孔产生固定的载频条纹,利用双旋转光楔实现剪切量的连续调节,采用正弦拟合算法进行相位计算.首先,分析了双孔调制的相位载频与双孔距和像距之间的关系,讨论了双旋转光楔得到线性剪切量调整的实验参数.然后,设计了测量光路参数;采用孔距为3.8 mm的双孔径配合焦距为80 mm的成像镜头在物距为300 mm时得到了载频为π/2的散斑场.最后,对动态形变的薄金属板进行了测量.实验结果表明:配合实时图像处理系统,该方法可以在帧率为15 frame/s的采集速度下实现动态形变的测量与显示,可测形变峰值为0.11～1.15 μm.本系统结构简单,易于集成,适用于动态形变的实时检测.     

Vacuum measurement using total-internal-reflection heterodyne interferometry

Based on the effect that the phase difference between s- and p-polarizations at the total-internal-reflection is changed with the variation of the air refractive index, which is related to the air pressure, a new optical method for measuring the air pressure of a vacuum cavity is proposed. From the experimental curve of the phase difference variation measured by the heterodyne interferometry and the calibrated pressure measurement of a vacuum cavity, an empirical formula is derived. With this empirical formula, the measurable range of this new optical method is 760 to 0.1 torr.     

Measurement optimum condition of speckle interferometry based on dual-camera technique

The speckle interferometer based on multi-camera technology using two cameras is applied to a dynamic deformation measurement of the package of an electronic device. To perform high precise measurement by this method, the optimum conditions for measurements are discussed concerning the size of speckle and the frequency of carrier signals. Under the optimum conditions, the deformation process of the package during the operation of an operational amplifier is measured. Then, the local maximum deformation can be estimated as 150 nm from experimental results. From the results, it can be also confirmed that electronic devices are deformed by the stress of a heat by an operation every second during the operating time.     

Multiplexing optical fiber low coherence and high coherence interferometric system with large range and high resolution for on-line measurement

A novel optical fiber sensing system multiplexing low coherence interferometry and high coherence interferometry that is endowed with large range and high resolution and is stabilized for on-line measurement is presented. An optical fiber Michelson interferometer performing measurement task in the system works in both modes of low coherence interferometry and high coherence interferometry simultaneously by employing a broadband light source and a fiber Bragg grating as an in-fiber reflective mirror. The amplitude of the measurand is determined by the low coherence interferometry while the value of the measurand is measured by the high coherence interferometry. Another optical fiber Michelson interferometer which is incorporated with the one performing measurement task stabilizes the sensing system for on-line measurement by exploiting an electronic feedback loop to reduce the influences that are resulted from environmental disturbances. The measurement range is 6 mm and the measurement uncertainty is less than 2 nm.     

Digital double-pulse holographic interferometry using Fresnel and image plane holograms

Different arrangements for digital double-pulse holographic and speckle interferometry for vibration analysis are described. In the case of digital double-pulse holographic interferometry, two separate holograms of an object under test are recorded within a few microseconds using a CCD camera and stored in a frame grabber. The phases of the two reconstructed wave fields are calculated from the complex amplitudes which are obtained by digital reconstruction of the wavefront produced by the hologram. The deformation is obtained from the phase difference. In the case of ESPI (or image plane hologram) the phase can be calculated by using the sinusoid-fitting method or the Fourier method. Using three directions of illumination and one direction of observation, all the information necessary for the reconstruction of the three-dimensional deformation vector can be recorded at the same time. Applications of the method for measuring rotating objects are discussed, together with the derotator needed.     

Measurement of specimen-induced aberrations of biological samples using phase stepping interferometry

Confocal or multiphoton microscopes, which deliver optical sections and three‐dimensional (3D) images of thick specimens, are widely used in biology. These techniques, however, are sensitive to aberrations that may originate from the refractive index structure of the specimen itself. The aberrations cause reduced signal intensity and the 3D resolution of the instrument is compromised. It has been suggested to correct for aberrations in confocal microscopes using adaptive optics. In order to define the design specifications for such adaptive optics systems, one has to know the amount of aberrations present for typical applications such as with biological samples. We have built a phase stepping interferometer microscope that directly measures the aberration of the wavefront. The modal content of the wavefront is extracted by employing Zernike mode decomposition. Results for typical biological specimens are presented. It was found for all samples investigated that higher order Zernike modes give only a small contribution to the overall aberration. Therefore, these higher order modes can be neglected in future adaptive optics sensing and correction schemes implemented into confocal or multiphoton microscopes, leading to more efficient designs.     

Study of lubricated impact using optical interferometry

An experimental study of lubricated impacts between a steel ball and a flat glass surface has been performed. The experimental set-up consists of a Ø70 mm ball mounted on a pendulum which impacts onto a lubricated glass disc. The contact region is studied by means of optical interferometry using a monochromatic light source, a microscope and a high-speed video recording equipment.

The lubricants are of PAO type and the viscosity ranges from 27 to 2600 mm² s⁻¹ at the test temperature. The impact velocity is varied between 0.08 and 0.29 m s⁻¹.

A dimple occurs at the centre of the contact where the lubricant is trapped. The influence of viscosity and impact velocity on the dimple's depth and diameter is studied.     

剪切散斑干涉术中剪切量的测量

由于采用剪切散斑干涉术测量离面应变和面内应变都与剪切量有关,所以剪切量的测量精度决定了应变场分布测量的准确性.本文论述了公式法、成像法、莫尔条纹法和相关法等4种剪切量测量法的测量原理,定性分析了它们的测量范围.搭建了一套剪切量测量系统,利用成像法、莫尔条纹法、相关法测量剪切散斑系统的剪切量,并以公式法计算的结果为准,比较其他3种方法的测量结果.结果表明:剪切量＞3 mm时,利用相关法测量具有较高的测量精度;剪切量＜3 mm时,奠尔条纹法测量效果会更好.因此,实际应用中,应该先根据实际测量条件估算剪切量的大致范围,然后依据估算范围选择合适的测量方法.     

Nanoscale surface deformation inspection using FFT and phase-shifting combined interferometry

In this paper, a flexible optical interferometer incorporated with both fast Fourier transform (FFT) and phase-shifting method is developed for three-dimensional (3D) testing of micro-components. Using light interference, microscopic optics, piezoelectric transducer (PZT) nanoscanning and a CCD camera, the proposed system can detect deformation and surface contour in the order of nanometers. An application of the proposed technique is demonstrated using two micro-components: a micro-beam in an accelerometer and a micromirror. The resulting interference fringes that are related to the deformation and surface contour are analyzed using FFT method or three-step phase-shifting method depending on the test surface features. Experimental results show the feasibility of the proposed method for 3D deformation and surface contour measurement of micro-components.