Bi-directional fringe counting interference refractometer

A bi-directional fringe counting interference refractometer has been developed primarily to measure the refractive index of air so that the accuracy of laser length measuring interferometer systems used in the free atmosphere can be maintained. Two signals suitable for electronic counting in phase-quadrature and sinusoidally related to path difference are produced by a technique that does not require any form of modulation and yet has the advantages of a modulated system. This refractometer is cheap to produce and easy to set up and align. Measurement sensitivity of 2.5 parts in 10⁷ for the refractive index of air can be obtained directly from the counting signals and this has been further improved by fringe sub-division. Comparisons with calculated values indicate that the refractometer can measure ambient refractive index in a laboratory without temperature control with an uncertainty approaching 1 part in 10⁷     

基于正弦相位调制的光纤干涉位移测量系统研究

针对全光纤干涉仪工作距离短、测量范围小等问题,提出了一种基于正弦相位调制的全光纤干涉系统,在参考臂通过电光调制器引入的调制参考光,与探头接收到的目标反射光产生干涉。根据锁相放大原理从干涉信号中提取出正交分量后,首先建立由正交分量构成的观测模型,通过卡尔曼滤波对正交分量的幅值和偏置进行迭代估计和修正,降低由相位延迟、调制深度漂移、寄生干扰等导致的幅值漂移和附加偏置;然后利用反正切法对反射光与参考光之间的相位差进行解调。开展了模拟干涉信号的相位解算仿真模拟和位移测量实验。仿真和实验验证了该算法解算相位的有效性。结果表明,该位移测量系统的工作距离可达到20 cm,测量精度为10 nm。     

基于单频激光干涉仪的精密工件台定位系统设计

激光干涉仪是以稳频氦氖激光波长为已知长度,利用迈克耳逊干涉系统测量位移的工具。近年来,激光干涉仪一直作为精密测量工具为精密加工机和工件台进行定位校准工作。本文介绍了一种基于单频激光干涉仪的精密工件台测量定位系统。本定位系统采用单频激光干涉仪作为精密测量工具,采用高档8位单片机作为数据处理微控单元,并基于VC＋＋语言编写相关控制软件。实际应用证明本系统定位速度快,精度高,理论上最小分辨率为58．6pm。     

Balanced homodyning for apertureless near-field optical imaging

A quadrature optical detection technique, based on polarized balanced-homodyne interferometry, has been developed for specific application to apertureless near-field scanning optical microscopy (ANSOM). With such technique, multiplicative background interference, inficiating quantitative optical imaging in standard homodyne-based ANSOM, can be suppressed. Periodic modulation of interferometric optical phase, typically employed in heterodyne-based ANSOMs even to such purpose, is not needed in the present configuration. Homodyne detection also facilitates detection of harmonic components of the ANSOM optical signal at the probe/sample distance modulation frequency, necessary for near-field discrimination and suppression of artifacts. Furthermore, since amplitude signal is not affected by phase fluctuations generated in the optical path of the interferometer, an optical fiber could be included in one interferometer arm, to couple the ANSOM head to the detection system, obtaining improved versatility of the instrument. A demonstration of the interferometer performance is given by a test confocal optical scan of a mirror surface. This technique, as applied to near-field microscopy, is anticipated to provide absolute values of optical contrast not depending on background interference and topography artifacts.     

基于空间相移技术的平面干涉仪系统设计

时域相移技术由于需要在时域采集多幅干涉图而只擅长用于静态检测。为改善测量的动态特性,现提出了基于空间相移技术的平面干涉仪系统。采用基于偏振干涉和光栅分光的单CCD成像空间相移系统设计方案,设计了具有折叠式布局特点的干涉仪光路系统,建立了系统机械结构三维模型,结构紧凑、调整方便,并运用四步相移算法进行了模拟试验后数据处理。结果表明,所设计系统能够满足动态测量要求。     

用空间载频法测量玻璃平板的厚度均匀性

设计了一种基于迈克耳逊干涉光路的相位测量系统,将单臂作为检测端完成了对玻璃平板厚度均匀性的直接测量和分析。该系统由CCD采集干涉图样,利用傅里叶变换条纹分析术和相位解包裹技术提取干涉图中所包含的待测相位信息;对于傅里叶变换法中频谱旁瓣中心无法准确定位的问题,采用三角变换法去载频,从而不需要准确地得知频谱旁瓣的中心位置就可以计算出相位结果,消除了人为估算和垂轴方向上的微小载频分量给测量结果带来的误差。实验测量了多块玻璃平板的厚度均匀性。测量结果显示：使用像元大小为4.65 μm×4.65 μm的CCD相机,测量玻璃平板两表面在长度方向和宽度方向上的厚度均匀性的理论精度分别达到0.93%和0.92%,表明本系统基本满足玻璃平板厚度均匀性测量的要求,且对干涉图频谱旁瓣的定位精度和载频的方向精度要求较低。     

半导体双波长透射式红外干涉仪的研制及应用

采用635nm波长半导体可见光激光和10.5μm波长半导体红外激光作为干涉光源,设计了635nm和10.5μm双波段共光路透射式红外干涉仪,实现了可见光波段干涉测试与红外光波段干涉测试共光路,且双光路共用可见光对准。双波段共用机械式相移系统,并采用635nm测试光分段驻点标定10.5μm测试时相移器的长行程误差。研制的双波长红外干涉仪系统的红外测试精度达到PV优于0.05λ,RMS优于0.02λ,系统重复性RMS优于0.001λ。采用该干涉仪测试口径为400mm×400mm,离轴量为800mm的离轴非球面,得到边缘最大偏差值为21.9μm,能够实现大口径离轴非球面从粗磨到精磨高精度加工面形的全过程干涉测试。     

Development of CO2 laser dispersion interferometer with photoelastic modulator

A dispersion interferometer is one of the promising methods of the electron density measurement on large and high density fusion devices. This paper describes development of a CO(2) laser dispersion interferometer with a photoelastic modulator for phase modulation. In order to make the dispersion interferometer free from variations of the detected intensity, a new phase extraction method is introduced: The phase shift is evaluated from a ratio of amplitudes of the fundamental and the second harmonics of the phase modulation frequency in the detected interference signal. The proof-of-principle experiments demonstrate the feasibility of this method.     

具有隔离器功能的激光干涉仪的研究

提出了一种具有隔离器功能的激光干涉仪.既可以进行干涉测量,又具有隔离器功能,可以防止反射光回到光源,使光源保持稳定,确保了测量精度.该干涉仪由常规干涉仪和双级隔离器的结构有机的结合起来,其中某些元件合二为一,使一个元件起到双重功能的作用,同时使干涉光路和隔离光路也相互重合起来.理论分析和实验研究表明:该方案是可行的.隔离度与双级隔离器的隔离度相同,达到了48dB.该装置的干涉测量精度与一般干涉仪一样取决于激光波长,但该装置结构紧凑,简化了测量系统,实际使用更为方便.     

A signal interpolation method for Fabry–Perot interferometer utilized in mechanical vibration measurement

In this investigation, a self-developed signal processing method for Fabry–Perot interferometer is proposed which can be utilized for high-speed dynamic displacement measurements, e.g. mechanical vibration measurements. The lookup table (LUT) integrated with the interference intensity equation has been employed for the interpolation processing of interference signals. With the aid of this method, the interpolation error has been reduced by 40% in comparison with that resulting from the commercial sinusoidal signal processing module. By operations of Fast Fourier Transform (FFT), the displacement measurement distribution can be converted into the frequency spectrum diagram. The interpolation resolution of the proposed interferometric displacement measurement system is about 0.1 nm. Experimental results demonstrate that this interferometer system is available for measuring frequencies till 2 kHz where its corresponding amplitude is 0.15 μm.     

基于圆偏振光合成的动态干涉仪同步移相技术研究

动态干涉仪是一种高精度的测量仪器,为了研究动态干涉仪的同步移相技术,论文通过建立两束旋向相反的圆偏振光合成的数学模型,更加清晰的表现了合成光束的传播状态,分析了合成光束经过起偏器后其干涉图像相位与起偏器摆放角度的关系.以此为基础,设计动态干涉仪光路并搭建试验台,最终用四个CCD同步采集到四幅相位依次相差90°的干涉图像,实现对被测镜面的动态测量,为提高干涉仪测量结果的准确性奠定了基础.     

全相位谱分析在自混合干涉位移测量中的应用

提出基于全相位谱分析的自混合干涉信号处理方法,用于减小激光自混合干涉位移测量的误差。首先,基于三镜法布里-珀罗腔模型介绍了自混合干涉系统的数学模型,分析了自混合干涉信号的产生机理和特性。然后,研究了弱反馈条件下自混合干涉位移测量方法,采用全相位谱分析算法进行相位测量,重构外部反射体位移曲线;讨论了信号处理算法原理并进行了算法仿真。最后,进行自混合干涉位移测量实验,并给出压电陶瓷位移测量实验结果。结果表明,全相位谱分析算法可将自混合干涉位移测量误差减小到4.4nm;应用全相位谱分析算法分析自混合干涉信号,可在不增加外部光学元件的前提下将位移测量误差减小到纳米量级。     

基于倾斜入射的直角棱镜大面测量装置研究

针对直角棱镜大面测量中可以消除多重干涉背景干扰的倾斜入射测量系统,设计了一种能直接进行直角棱镜大面测量的正置式倾斜入射干涉仪装置.该装置包括相移干涉仪主机、一体化载物工作台以及一对参考平晶.讨论了直角面参与反射带来的光线簇造成的多重干涉背景误差,采用3D偏折的方法来避免全内反射光干扰直角棱镜大面测量.实验部分,组装了基...     

Shape measurements of mirror surfaces with a lateral-shearing interferometer during machine running

A common path lateral-shearing interferometer with a minimum number of optical components has been developed. Because the interferometer is little affected by mechanical vibrations and air turbulence, it can be mounted on an ultraprecision lathe and can be used to measure the shapes of workpieces. A plane parallel glass plate is used to shear the wavefront under test in the interferometer. To analyze the interference fringes obtained by the interferometer precisely, a fringe-scanning method using a slight tilt of the glass plate is used. Zone plates that are computer-generated holograms are used to measure spherical and aspherical surfaces with the interferometer. A spherical and a parabolic concave mirror were measured with the interferometer. The spherical mirror was also measured by a Fizeau interferometer to compare the error with that measured by the lateral-shearing interferometer. The experimental results agreed well with those measured by the lateral-shearing interferometer.     

Subnanometric calibration of a differential interferometer

A novel self-calibration method is proposed for calibrating differential interferometers with subnanometer resolution, and the basic characteristics of the method are discussed. Analysis shows that without using any external reference, the calibration accuracy approaches the resolution limit of the interferometer, which is determined by the signal-to-noise ratio (SNR) and the stability of the measurement system. A compact differential interferometer that uses a laser diode as the light source has been developed in order to demonstrate the viability of the proposed calibration method. The conventional fringe-counting and phase modulation methods are combined in order to extend the measurement range and improve the resolution of the interferometer. The developed interferometer was calibrated using the new method, and the calibration results were compared to those obtained by a comparison calibration method that uses a capacitance displacement sensor as the reference.     

A proposed design for a polarization-insensitive optical interferometer system with subnanometric capability

A bidirectional, fringe-counting, two-beam interferometer system is described that can be used for precision length measurement with any laser source that is adequately coherent for the application. The two electrical phase-quadrature signals required for bidirectional electronic counting are obtained from photodetectors at the two interferometer outputs. A thin metal film design for the beam-splitter coating introduces the required phase difference of nearly 90° for both the perpendicular and parallel polarization components. Electronic alignment and control are performed by a system used to continuously monitor the signals produced from the outputs and automatically process these signals to achieve the optimum performance from the interferometer. Interferometers using the technique require a limited amount of optical alignment and all of the electronic adjustments are automatically controlled by the electronic system. These instruments are economical to manufacture and easy to apply in practice, readily achieving subnanometric accuracy in the measurement of changes in optical path.     

白光干涉表面结构测量仪的优化设计与应用

为测量微机电系统的表面结构,研制了一种基于白光干涉法的表面结构测量仪。设计了显微干涉仪,通过实验分析了显微干涉仪关键设计参数中的光源带宽、物镜数值孔径、孔径光阑大小对垂直扫描白光显微干涉测量中干涉条纹光强分布的影响;设计了Z向一维位移工作台,提出了一种以显微干涉图像灰度值归一化标准方差为依据的白光干涉测量条纹自动搜索定位方法。相关实验结果为白光干涉表面结构测量仪的优化设计提供了参考依据。     

激光干涉仪数字测角的新方法及其应用

介绍了一种基于迈克耳孙干涉仪的精密角度测量系统,该系统利用迈克耳孙干涉仪在几何量测量中的干涉测量技术,通过转换将角位移转换为可以反映干涉光路中光程差变化的线位移,并通过相应电路对干涉条纹进行处理,从而实现了对大转角的精密测量。与以往类似系统相比,该系统具有结构简单、误差恒定、测量精度高、测角范围大、易于数字化等特点。同时,文章还对系统的构成原理、设计注意事项和精度等作了有关的理论分析。     

Volumetric phase-measuring interferometer for three-dimensional coordinate metrology

We present a volumetric interferometer that has been specially designed to improve the measurement accuracy of the three-dimensional coordinate metrology by reducing excessive Abbe offsets. The interferometer is composed of two main parts; one is a three-dimensionally movable target and the other is a stationary two-dimensional array of photo-detectors. The target made of point diffraction sources emanates two spherical wavefronts, of which interference intensity is monitored by the photo-detectors. Applying phase shifting allows the phases of the photo-detectors to be precisely obtained, and the measured phases are fitted to a geometric model of multilateration so as to determine the xyz-location of the target by minimizing least square errors. A prototype built on a CMM demonstrates that the proposed interferometer is capable of measuring the xyz-coordinates of the probe with a volumetric uncertainty of less than 1.0 μm.     

Fringe counting method for synthetic phase with frequency-modulated laser diodes

Fringe counting method with laser diodes (LDs) for displacement measurement has been constructed. Two LDs are frequency modulated by mutually inverted sawtooth currents on an unbalanced two-beam interferometer. The mutually inverted sawtooth-current modulation of LDs produces interference fringe signals with opposite signs for respective wavelengths. The two fringe signals are fed to an electronic mixer to produce a synthetic fringe signal with a reduced sensitivity to the synthetic wavelength. Synthetic fringe pulses derived from the synthetic fringe signal make a fringe counting system possible for faster movement of the tested mirror.