Development of a diffraction-type optical triangulation sensor

We propose a diffraction-type optical triangulation sensor based on the diffraction theorem and the laser triangulation method. The advantage of the proposed sensor is that it obtains not only the linear displacement of a moving object but also its three angular motion errors. The developed sensor is composed mainly of a laser source, two quadrant detectors, and a reflective diffraction grating. The reflective diffraction grating can reflect the incident laser beam into several diffractive rays, and two quadrant detectors were set up for detecting the position of 0- and + 1-order diffraction rays. According to the optical triangulation relationship between the spatial incident angles of a laser beam and the output coordinates of two quadrant detectors, the displacement and the three angular motion errors of a moving object can be obtained simultaneously.     

An overview and a contribution to the optical measurement of lineardisplacement

The present work is a contribution to the field of linear displacement measurements by optical means. For that purpose, a brief overview of some existing solutions is presented and two systems for axial linear displacement measurement based on light intensity detection are introduced. The systems have redundancy and were designed with the purpose of achieving identification and automatic correction of errors arising from inadvertent angular variations between the sensor and the light beam positions     

Simple three-dimensional laser angle sensor for three-dimensional small-angle measurement

A simple three-dimensional (3D) laser angle sensor for 3D measurement of small angles based on the diffraction theorem and on ray optics analysis is presented. The possibility of using position-sensitive detectors and a reflective diffraction grating to develop a 3D angle sensor was investigated and a prototype 3D laser angle sensor was designed and built. The system is composed of a laser diode, two position-sensitive detectors, and a reflective diffraction grating. The diffraction grating, mounted upon the rotational center of a 3D rotational stage, divides an incident laser beam into several diffracted rays, and two position-sensitive detectors are set up for detecting the positions of +/-1st-order diffracted rays. According to the optical path relationship between the three angular motions and the output coordinates of the two position-sensitive detectors, the 3D angles can be obtained through kinematic analysis. The experimental results show the feasibility of the proposed 3D laser angular sensor. Use of this system as an instrument for high-resolution measurement of small-angle rotation is proposed.     

Experimental and simulated angular profiles of fluorescence and diffuse reflectance emission from turbid media

Given the wavelength dependence of sample optical properties and the selective sampling of surface emission angles by noncontact imaging systems, differences in angular profiles due to excitation angle and optical properties can distort relative emission intensities acquired at different wavelengths. To investigate this potentiality, angular profiles of diffuse reflectance and fluorescence emission from turbid media were evaluated experimentally and by Monte Carlo simulation for a range of incident excitation angles and sample optical properties. For emission collected within the limits of a semi-infinite excitation region, normalized angular emission profiles are symmetric, roughly Lambertian, and only weakly dependent on sample optical properties for fluorescence at all excitation angles and for diffuse reflectance at small excitation angles relative to the surface normal. Fluorescence and diffuse reflectance within the emission plane orthogonal to the oblique component of the excitation also possess this symmetric form. Diffuse reflectance within the incidence plane is biased away from the excitation source for large excitation angles. The degree of bias depends on the scattering anisotropy and albedo of the sample and results from the correlation between photon directions upon entrance and emission. Given the strong dependence of the diffuse reflectance angular emission profile shape on incident excitation angle and sample optical properties, excitation and collection geometry has the potential to induce distortions within diffuse reflectance spectra unrelated to tissue characteristics.     

表面等离子共振双光束差分研究和数值模拟

为提高光强调制型表面等离子共振传感器的灵敏度和抗干扰能力,本文提出了一种采用双光束差分光强的SPR检测新方法.通过对该方法的理论计算和数值模拟分析,得到了不同入射角和不同金膜厚度时,反射光强差与样品折射率之间的关系曲线.研究表明,与传统的光强调制方法相比,当两束光入射角相差5°,金膜厚度在40～50 nm时,该方法是有更高的灵敏度和更宽的测量范围,并且由于采用了光强差分技术,大大提高了传感器的抗干扰性和稳定性.     

Geometrical-optics approximation of forward scattering by gradient-index spheres

By means of geometrical optics we present an approximation method for acceleration of the computation of the scattering intensity distribution within a forward angular range (0-60 degrees ) for gradient-index spheres illuminated by a plane wave. The incident angle of reflected light is determined by the scattering angle, thus improving the approximation accuracy. The scattering angle and the optical path length are numerically integrated by a general-purpose integrator. With some special index models, the scattering angle and the optical path length can be expressed by a unique function and the calculation is faster. This method is proved effective for transparent particles with size parameters greater than 50. It fails to give good approximation results at scattering angles whose refractive rays are in the backward direction. For different index models, the geometrical-optics approximation is effective only for forward angles, typically those less than 60 degrees or when the refractive-index difference of a particle is less than a certain value.     

Simple wide-range method for angle measurement with a point fiber-optic output

We propose a simple optical method for precise, wide-range angle measurement based on the use of a single-mode optical fiber as a registration scheme output. Because of its micrometric core dimensions, the fiber serves as a point receiver that is highly sensitive to angular displacements of focused laser emission. The method allows the independent photoelectric measurement of both rotation and spatial angles of various optical elements, combining a wide angular dynamic range (from 0 degrees to 360 degrees ) with high accuracy (exceeding 3 arcsec).     

Straightness measurements by use of a reflection confocal optical system

Straightness measurement is a very important technique in the field of mechanical engineering. A particular application for straightness measurement is high-accuracy machining on a diamond-turning lathe. We propose a novel, to our knowledge, optical method for measuring the straightness of motion, and its mathematical analysis is outlined. The technique is based on measurement of the lateral displacement of point images by use of reflection confocal optical systems. The advantages of this method are that (i) the lateral displacements in the direction of the two axes perpendicular to the optical axis can be measured, (ii) the rotation angles around all three axes can be measured, and (iii) reflection optical systems are more compact in length than are transmission optical systems.     

Design of angle-tolerant multivariate optical elements for chemical imaging

Multivariate optical elements (MOEs) are multilayer optical interference coatings with arbitrary spectral profiles that are used in multivariate pattern recognition to perform the task of projecting magnitudes of special basis functions (regression vectors) out of optical spectra. Because MOEs depend on optical interference effects, their performance is sensitive to the angle of incidence of incident light. This angle dependence complicates their use in imaging applications. We report a method for the design of angle-insensitive MOEs based on modification of a previously described nonlinear optimization algorithm. This algorithm operates when the effects of deviant angles of incidence are simulated prior to optimization, which treats the angular deviation as an interferent in the measurement. To demonstrate the algorithm, a 13-layer imaging MOE (IMOE, with alternating layers of high-index Nb2O5 and low-index SiO2) for the determination of Bismarck Brown dye in mixtures of Bismarck Brown and Crystal Violet, was designed and its performance simulated. For angles of incidence that range from 42 degrees to 48 degrees, the IMOE has an average standard error of prediction (SEP) of 0.55 microM for Bismarck Brown. This compares with a SEP of 2.8 microM for a MOE designed by a fixed-angle algorithm.     

Ellipsometry of anisotropic (sub)nanometric dielectric films on absorbing materials

A new ellipsometric method was developed for determining optical parameters of ultrathin uniaxially anisotropic dielectric films. It is based on the phase conversion measurements of polarized reflected light at different incident angles. The elaborated technique possesses very high sensitivity and is successfully applicable even for sub-nanometric layers because the phase changes for such layers on absorbing substrates are generally markedly greater than the measurement error. Another interesting facet of this method lies in the fact that the traditional model-based regression analysis is not used for data handling. The inversion problem is resolved on the basis of an original analytical approach, which has no need of initial guesses for the desired parameters. The presented method is tested using a numerical simulation.     

Transmission-type angle deviation microscopy

We present a new microscopy technique that we call transmission angle deviation microscopy (TADM). It is based on common-path heterodyne interferometry and geometrical optics. An ultrahigh sensitivity surface plasmon resonance (SPR) angular sensor is used to expand dynamic measurement ranges and to improve the axial resolution in three-dimensional optical microscopy. When transmitted light is incident upon a specimen, the beam converges or diverges because of refractive and/or surface height variations. Advantages include high axial resolution (approximately 32 nm), nondestructive and noncontact measurement, and larger measurement ranges (+/- 80 microm) for a numerical aperture of 0.21 in a transparent measurement medium. The technique can be used without conductivity and pretreatment.     

Holographic common-path interferometer for angular displacement measurements with spatial phase stepping and extended measurement range

A novel technique for extending the unambiguous measurement range for differential measurements of angular deflections is presented. The technique utilizes a common-path interferometer that simultaneously probes the out-of-plane displacement of three points on the object surface. The system is based on a single laser diode, and all the optical functions of the system are implemented in a dedicated holographic optical element (HOE). The HOE automatically provides spatially phase-stepped interference signals for real-time phase measurement. It is therefore not necessary to employ any polarizing optics or active elements to introduce the phase stepping. The common-path scheme combined with the HOE provides a system that is inherently stable, since the HOE operates as both transmitter and receiver in the system. The system is compact, is robust, and has the potential for being mass-produced at a low cost and is thus well suited for industrial use, such as in commercial vibrometers. The technique is demonstrated in a system for measuring angular deflections of a plane mirror. The technique, however, is not restricted to this use alone and can easily be configured to probe other types of surface displacements, e.g., the deflection of a diaphragm. In the present configuration, the system can measure angular deflections with a sensitivity of 2.5 x 10(-7) rad over a measurement range that is approximately 3.5 x 10(-3) rad, i.e., a dynamic range of approximately 1:14,000. Furthermore, the system can easily be reconfigured for a desired angular sensitivity and measurement range.     

Uncertainty analysis of displacements measured by in-plane electronic speckle-pattern interferometry with spherical wave fronts

Displacement measurements by optical interferometry depend on the induced phase difference and on the interferometer's sensitivity vector; the latter depends in turn on the illuminating sources and on the geometry of the optical arrangement. We have performed an uncertainty analysis of the in-plane displacements measured by electronic speckle-pattern interferometry with spherical incident wave fronts. We induced the displacements by applying a uniaxial tensile load on a nominally flat elastic sample. We approached the displacement uncertainty by propagating the uncertainties that we considered reasonable to assign to the measured phase difference and to the characteristic parameters of the interferometer's sensitivity vector. Special attention was paid to evaluating contributions to the displacement uncertainty. Moreover, we observed that the uncertainty decreases if the angles of incidence and the source-target distances are increased.     

Alignment of an interferometric gravitational wave detector

Interferometric gravitational wave detectors are designed to detect small perturbations in the relative lengths of their kilometer-scale arms that are induced by passing gravitational radiation. An analysis of the effects of imperfect optical alignment on the strain sensitivity of such an interferometer shows that to achieve maximum strain sensitivity at the Laser Interferometer Gravitational Wave Observatory requires that the angular orientations of the optics be within 10(-8) rad rms of the optical axis, and the beam must be kept centered on the mirrors within 1 mm. In addition, fluctuations in the input laser beam direction must be less than 1.5 x 10(-14) rad/ radicalHz in angle and less than 2.8 x 10(-10) m/ radicalHz in transverse displacement for frequencies f > 150 Hz in order that they not produce spurious noise in the gravitational wave readout channel. We show that seismic disturbances limit the use of local reference frames for angular alignment at a level approximately an order of magnitude worse than required. A wave-front sensing scheme that uses the input laser beam as the reference axis is presented that successfully discriminates among all angular degrees of freedom and permits the implementation of a closed-loop servo control to suppress the environmentally driven angular fluctuations sufficiently.     

Instantaneous spatially resolved acquisition of polarimetric and angular scattering properties in optical coatings

A CCD angular resolved scattering setup is presented. This new high sensitivity instrument allows both spatial and angular resolved measurement of scattered field intensity and polarimetric features. Applications to the comprehensive characterization of optical coatings are given.     

半光斑成像式多功能激光瞄准测头的研究

运用半光斑成像原理设计了一种用于三坐标测量机的多功能激光瞄准测头。详细介绍了测头的光学系统工作原理和设计思路,采用自适应控制方法实时调节激光光强使其可以适应不同光学特性表面的瞄准测量,并进行了多功能测头的重复性瞄准测量、灵敏度测量、倾角跟踪实验。实验结果表明,该测头重复性瞄准测量不确定度优于1 μm,测量灵敏度可达30 mV/μm,激光跟踪瞄准被测曲面倾角可达25°,能满足三坐标测量机的使用要求。该测头具有检测速度快、自动化程度高、瞄准精度高的特点,结合三坐标测量机或者其它测长仪器,能够实现对自由曲面进行快速精确瞄准及轮廓图像瞄准测量,具有广泛的应用前景和实用价值。     

基于机器视觉的光纤准直器自动耦光系统

针对以往无源光器件自动耦光系统耦光耗时长的问题,提出一种基于机器视觉的准直器自动粗对光解决方案。应用工业相机采集待调准直器图像;结合改进后的OTSU二值化算法与概率霍夫直线检测算法,提取待调准直器的轮廓线并计算两准直器之间的角度位置差;根据角度位置差,控制系统会发送相应数量的脉冲控制自动平台实现运动控制。以上3个环节相互配合形成闭环控制,通过多次反复调节完成准直器自动粗对光。实验结果表明,使用机器视觉直接定位准直器可以在较短时间内完成粗对光,实际对光时间少于15 s,对光完成后两准直器各角度夹角均小于0.5°,各方向位移差均小于100μm,接收端插损小于30 dBm。     

远距离高精度多普勒位移测量

通过泛函、激光散斑理论和随机过程各态遍历的研究,导出激光多普勒信号强度与聚焦光斑直径、接收透镜通光口径、光电接收器响应等参数间的关系,在此基础上设计出一种适用于远距离处面内位移测量的光路。此光路将高斯光束束腰聚焦在被测体上,实现最小聚焦光斑和平面波叠加,此外采用大口径透镜接收散射光,用响应度高的光电接收器转换光电信号等措施获得高强度高信噪比的测量信号。将此光路用于 100m 处面内位移(49.70mm)测量,其精度可达 2%。此设计方法能用于振动或地震波的高精度检测。     

基于线激光传感器的工件尺寸测量系统的误差补偿方法

提出了一种基于线激光传感器的工件尺寸测量系统的误差补偿方法,利用坐标系投影和图像处理技术进行误差补偿。设定传感器坐标系OM-XMYMZM和设备坐标系O-XYZ,分析坐标轴夹角φ、δ、γ对工件尺寸坐标值X、Y、Z的误差,建立了基于φ、δ、γ在XOY、YOZ、XOZ平面上的投影角α、β、θ的误差补偿模型。利用图像处理技术测得α、β、θ,计算经过误差补偿的工件尺寸坐标值X′、Y′、Z′。对尺寸100mm×100mm×10mm的长方体工件进行测量实验,分别测量了长度、宽度、圆心距、圆直径、圆线距、台阶高度。测量结果表明:经误差补偿后的工件尺寸测量误差在40μm以内,优于未补偿前的520μm;均方根误差低于40μm,优于未补偿前的580μm。其中,圆心距误差补偿效果最显著,测量误差减小了560μm;圆直径误差补偿效果最不明显,测量误差减小了10μm。     

A Method for the Optical Characterization of Thin Uniaxial Samples

An optical characterization procedure for small fragments of uniaxial materials is described involving the simple use of crossed polarizers with one polished face of the material. The reflectance at a fluid-uniaxial slab boundary beyond, but near, the critical angle of incident light is examined for linear incidence polarization using an orthogonal output polarizer. It is found that, as the crossed incident and output polarizers are rotated together, there are, for a given angle of incidence, particular polarization angles for which the reflectivity is a minimum. These angles give information on the optical tensor of the crystal under study. Further the intensity of the reflected light, for incidence angles beyond critical with the input and output polarizers crossed, has as a function of the incident polarization angle an oscillatory form which, when fitted to theory, can also yield the full uniaxial tensor of the material under study. This is confirmed experimentally for a thin single crystal of calcite with one polished face.