一维PSD定位精度的实验研究

本文根据实验研究测试了一维(二象限)PSD的线性特性,光斑大小和光束倾斜对PSD定位精度的影响,同时分析了其它一些因素的影响。实验表明,1mm直径的He—Ne激光束定位精度2.5μm,光斑越大,倾斜角越大,PSD的定位精度越低。PSD的线性性除与入射光能量有关外,还与后续处理电路有关。     

Calculation of the power spectral density from surface profile data

The power spectral density (PSD), in its two-dimensional form, has been designated as the preferred quantity for specifying surface roughness on a draft international drawing standard for surface texture. The correct calculation of the one-dimensional PSD from discrete surface profile data is given, and problems in using fast Fourier-transform routines that are given in some of the standard reference books are flagged. The method given here contains the correct normalizing factors. Two ways to reduce the variance of the PSD estimate are suggested. Examples are shown of the variance reduction possible in the PSD's.     

Single-beam data encoding using a holographic angular multiplexing technique

We propose a novel configuration for angular multiplexing holographic encoding in which the signal beam and the reference beam are combined into a single beam. By using a spatial light modulator based on twisted nematic liquid crystals, the signal and the reference beams are modulated in amplitude mode and phase mode, respectively. The multiplexed interference patterns with the reference beams of different incident angles are recorded near the Fourier transform plane, and then the signals are selectively reconstructed by the corresponding reference beam. Both the simulation and the experiment of single-beam angular multiplexed holography are performed with consistent results. Compared with the traditional angular multiplexing holographic recording system, the single-beam configuration is more compact, easier to adjust, and less sensitive to the vibration of the environment. Therefore, it will be more attractive for potential applications in many fields, such as high-density signal recording and data encryption.     

位置敏感探测器统一结构模型的分析

基于统一的二阶RC传输线模型结构,推导出一维和二维PSD光生电势的解析解,并进行了仿真分析。仿真结果表明,一维PSD的光生等势线在没有电极的两边界垂直分布,并能够真实探测到光入射位置;而二维PSD的光生电势分布以光源照射位置为中心向四个电极递减,垂直方向互相影响,在给定参数下光的入射位置与真实值相比有60%的误差。PSD统一结构模型的分析方法和仿真结果对计算激励脉冲响应、短脉冲激励的位置精度分析、光生电势分析提供了一个理论指导。     

Calculation of the radiation trapping force for laser tweezers by use of generalized Lorenz-Mie theory. I. Localized model description of an on-axis tightly focused laser beam with spherical aberration

Calculation of the radiation trapping force in laser tweezers by use of generalized Lorenz-Mie theory requires knowledge of the shape coefficients of the incident laser beam. The localized version of these coefficients has been developed and justified only for a moderately focused Gaussian beam polarized in the x direction and traveling in the positive z direction. Here the localized model is extended to a beam tightly focused and truncated by a high-numerical-aperture lens, aberrated by its transmission through the wall of the sample cell, and incident upon a spherical particle whose center is on the beam axis. We also consider polarization of the beam in the y direction and propagation in the negative z direction to be able to describe circularly polarized beams and reflected beams.     

Reflection and refraction of narrow Gaussian beams with general astigmatism at tilted optical surfaces: a derivation oriented toward lens design

The formulas for the reflection and refraction of a narrow Gaussian beam with general astigmatism at a tilted optical surface are derived by ray-tracing techniques. The propagation direction of the reflected and refracted beams is computed by tracing the central ray of the incident beam, and the characteristic parameters of the respective wavefronts are worked out by applying the formulas developed for the generalized ray tracing. Moreover, the Gaussian form of the reflected and refracted amplitude distributions along the transverse coordinates is determined by requiring the matching of the incident, reflected, and refracted light spots on the optical surface. No limiting assumptions are made regarding the form of the optical interface or the orientation of the incident astigmatic wavefront. In the end, to illustrate a simple application of these formulas, the reflection of a Gaussian beam at a conicoid is considered, and a simple property of the conicoidal mirrors is reported.     

弹体冲击下测量光束的偏摆修正研究

光栅作为瞬态高速激光测速仪测量过程中的合作目标,其表面的技术状态决定了激光多普勒信号的质量.特别是在弹体高速冲击条件下,极易造成光栅内部结构发生损坏,导致反射光无法入射至探测器敏感部.因此,本文采用LS-DYNA仿真软件对砧体结构与光栅的连接处展开分析,并获取表面处的应力应变分布,从而为光栅结构的布置方式提供参考依据....     

Oblique incidence and observation electronic speckle-pattern interferometry

In this paper we discuss an oblique incidence and observation electronic speckle-pattern interferometer, in which we use an anamorphic prism in front of the object. A collimated beam traveling through the prism is partly reflected at the base of the prism. The reflected light is the reference beam and the transmitted light illuminates the diffuse object, thereby generating the object beam. In this scheme the object and the reference beams are collinear. A new scheme that uses two prisms and permits phase stepping is also presented.     

Analytical model of Doppler spectra of coherent light backscattered from rotating cones and cylinders

The interaction between a rotating object and laser beams has been studied in the field of laser Doppler velocimetry, where two incident laser beams are focused on one small spot of the rotating surface and interferometry is used. In the case of a single incident laser beam illuminating a relatively large area of the rotating surface, both the Doppler broadening and the reflected-power level are dictated by points distributed over a wide curved area at varying angles of incidence. An analytical model of spectra in backscatter from cones and cylinders rotating around their axes is presented. This analytical solution may contribute to laser Doppler velocimetry as well as ladar applications.     

Measurement of displacement and vibration by using the oblique ray method

An optical system that can measure vibrations and displacements is developed by using the oblique ray method. By employing a single convex lens that plays both roles of sending and receiving the beams that are reflected by the target surface, the optical measurement system became compact and reliable. A position-sensitive detector is used to measure the position change of the beam spot on the target surface. The resolution of the optical system can be controlled by changing the optical magnitude of the objective lens and is designed to be less than 0.1 microm for the developed system.     

Unified theory for parallel and focused beam nonspecular reflection at liquid-solid interfaces

Summary This paper presents a theoretical model based on wave mechanics for the reflection of focused and parallel ultrasonic beams from a liquid-solid interface. The incident beam is defined by a Gaussian velocity distribution along a plane emitter, and the reflected beam is described through its pressure field by means of asymptotic analysis based on the short wave hypothesis. In the case of a focused reflected beam, nonspecular phenomena are observed for any angle of incidence. However, in the case of a parallel reflected beam, nonspecular reflection only occurs if the incidence of the beam is in the neighborhood of the Rayleigh angle. The objective of this paper is to discuss in detail the physical mechanisms of nonspecular reflection for both focused and unfocused beams and to provide an understanding of the complex phenomena related to nonspecular reflection of ultrasonic beams, which plays an important role in scanning acustic microscopy for materials nondestructive characterization.     

High-Quality Brewster's Angle Polarizer for Broadband Infrared Application

We have designed and constructed a linear polarizer for use with visible and infrared radiation. The broadband polarizer consists of four germanium plates arranged in a chevron geometry. Input radiation is incident near Brewster's angle for the first plate such that the reflected beam is preferentially s-wave polarized. This reflected beam is steered subsequently to the successive plates, always intersecting near Brewster's angle. The beam polarization at the output of the device is almost completely s-wave polarized. The ratio of the paraxial flux of the nearly extinguished p-wave polarized light to the s-wave polarized light transmitted through the device is found to be less than 10(-5) for laser illumination at wavelengths of 0.633, 1.32, 3.39, and 10.6 mum. Calculations predict that extinction ratios less than 10(-5) are achievable over the wavelength range from 0.4 mum to beyond 500 mum. Alternative design geometries involving fewer plates are also described along with their advantages and disadvantages.     

Photorefractive Beam splitter for Free-Space Optical Interconnections

A photorefractive beam splitter (PRBS) is introduced as an alternative to a polarizing beam splitter (PBS) for coupling optical power into reflective modulators in a free-space optical interconnection system. The PRBS uses a single diffraction grating recorded in a photorefractive material to redirect the incident laser light into the first diffraction order and onto the modulators. Reflected interconnection light not matching the Bragg angle criteria transmits uncoupled through the beam splitter. Experimental results show that the PRBS provides better, more uniform transmission for off-axis beams than the currently used PBS.     

Device for magneto-optic signal detection with a small crystal prism

A device made of a birefringent crystal for signal detection of magneto-optic (MO) disks is presented. The light beam from a MO disk is separated into two orthogonally polarized components at the surface of a birefringent prism. After these two components are reflected by the top and the bottom surfaces of the prism inside, at the detector they become sufficiently separated from each other for discrete detection, even though the prism is small. A method for calculating the light intensities and the positions of focused beams in a birefringent prism and the results of a fundamental experiment are presented.     

Efficient deconvolution of noisy periodic interference signals

The interference signal formed by combining two coherent light beams carries information on the path difference between the beams. When the path difference is a periodic function of time, as, for example, when one beam is reflected from a vibrating surface and the other from a fixed surface, the interference signal is periodic with the same period as the vibrating surface. Bessel functions provide an elegant and efficient means for deconvoluting such periodic interference signals, thus making it possible to obtain the displacement of the moving surface with nanometer resolution. Here we describe the mathematical basis for the signal deconvolution and employ this technique to obtain the amplitude of miniature capillary waves on water as a test case.     

Integrated Optics for Astronomical Interferometry. III. Optical Validation of a Planar Optics Two-Telescope Beam Combiner

The optical characterization of a fiber-connected planar optics beam combiner dedicated to astronomical interferometry for two telescopes is presented. The beam combiner, fully integrated on a single 5 mm x 40 mm glass chip, is tested as the central part of an astronomical instrument. The single-mode waveguides are made by silver-ion-exchange technology upon glass substrates and provide spatial filtering, which improves the visibility measurement accuracy by selecting only the fundamental mode of the beams at the telescope focal plane. A global optical throughput of 43% is measured, and the sources of losses are identified and examined in detail. Solutions for improving this throughput are proposed. High and stable contrasts are obtained with a 1.55-mum laser diode (?96%) and with a white-light source (~92%) in the astronomical H filter (1.43 mum; 1.77 mum). The need for accurate control of differential instrumental polarization is demonstrated. In this context the intrinsic polarization-maintaining property of the planar optics component is characterized. This validation of the important potential uses of integrated planar optics should be valuable for future design of optical telescope arrays.     

Multipoint laser Doppler vibrometry with single detector: principles, implementations, and signal analyses

A 20-point laser Doppler vibrometer with single photodetector is presented for noncontact dynamic measurement. A 5×4 beam array with various frequency shifts is generated by a 1.55 μm distributed feedback laser and four acousto-optic devices, and illuminating different points on vibrating objects. The reflected beams are coupled into a single-mode fiber by a pigtailed collimator and interfere with a reference beam. The signal output from a high-speed photodetector is amplified and then digitized by a high-speed analog-to-digital converter with a sampling rate of 1 gigasample per second (1 GS/s). Several methods are introduced to avoid the cross talk among different frequencies and extract the vibration information of 20 points from a one-dimensional signal. Two signal processing algorithms based on Fourier transform and windowed Fourier transform are illustrated to extract the vibration signals at different points. The experimental results are compared with that from a commercial single-point laser vibrometer. The results show simultaneous vibration measurement can be realized on multiple points using a single laser source and a single photodetector.     

Design and analysis of an optoelectronic inclinometer for simultaneous measurement of inclinations along two orthogonal directions

Conventional inclination measurement systems such as precision vials and capacitance measuring systems can measure inclination in only one direction at a time. We present what is believed to be a new optoelectronic system that can measure inclination angles along two orthogonal directions simultaneously by using a simple pendulum, two mirrors, a 2D position-sensing detector (PSD), and a laser diode. The light ray from the laser is projected onto a mirror that is fixed to a pendulum whose relative angle modifies in response to inclination changes of the inclinometer's housing. The light ray reflected by the mirror is sensed by the PSD, after which the signal can be interpreted by a PSD signal processor, recorded, or output to a computer. This study uses skew-ray tracing methodology to obtain implicit nonlinear system equations to model the relations of the relative inclination angles of the various components, PSD position, and world frame. A first-order Taylor series expansion is used to obtain a linear form of the system equations. To validate the proposed methodology, an actual prototype system is built and experimental results show that the performance of this system is excellent.     

Noncontact single-fiber-optic proximity sensor using a laser-fabricated tap

We have developed a simple, noncontact, fiber-optic proximity sensor, using a laser micromachined tap on a single multimode optical fiber. The fiber end is placed near a target surface, and a beam of light is incident from the fiber onto the target. Some fraction of this light is reflected or scattered by the target and coupled back into the fiber. The amount recoupled into the fiber is dependent on the distance between the fiber end and the target surface as well as on other parameters such as the target's surface roughness. The fiber-optic tap allows us to monitor both the initial amount of light launched down the fiber toward the target and the amount of backreflected light from the target. For a known environment and target surface, variations in source intensity can be compensated for by monitoring the ratio of the two counterpropagating beams.     

Lateral displacement and its mechanism in asymmetric layered configuration

Lateral displacement and its mechanism in asymmetric layered configuration are investigated. It is shown by the stationary-phase approach that displacements of both the transmitted and reflected beams can be positive as well as negative, and their magnitude can be greatly enhanced at transmission resonances. Numerical simulations show that for a well-collimated incident beam, if the norms of transmission and reflection coefficients are approximately constant within the peak of the angular-spectrum distribution of the beam, the transmitted and reflected beams can undergo lateral displacement without distortion, as long as the thickness of the layer satisfies a restriction. It is concluded that lateral displacement is not caused by beam distortion, but the result of reshaping the multiply transmitted (or reflected) beams.