Measurement of surface figure of plane optical surfaces with polarization phase-shifting Fizeau interferometer

A Fizeau interferometer based set up for measurement of surface forms of plane optical surfaces has been discussed. Phase shifting interferometry has been applied using polarization phase shifter. A linearly polarized (632.8 nm) He–Ne laser has been used as the source. Light reflected from the object and the reference/master surfaces are made circularly polarized in opposite senses by means of two properly oriented quarter wave retardation plates placed at appropriate positions, one inside and other outside the interference cavity of the interferometer, and phase shifts are introduced between the object and the reference/master waves by varying angular orientation of a polarizer/analyzer. Final result is made free from any residual wave-front aberrations introduced by the (intra-cavity) wave plate by subtracting phase values obtained by PSI technique between a high optical quality master surface and the reference surface from that obtained for the test object surface with respect to the same reference surface for each point of the interference field. Results are shown for a plane surface.Advantages of the technique presented are linearity and high accuracy in phase stepping, no perturbation of the interference cavity during the phase shifting and possibility of real time or dynamic interferometry.     

基于多光束干涉原理的相移算法研究

针对多光束干涉原理的相移算法包括算法误差及步长优化等问题，以菲索干涉仪精密测长为 应用背景进行了研究.利用干涉光学的基本原理导出了在多束光干涉(经光学面多次反射、透 射)的情况下干涉光强随相位分布的精确公式；在此基础上，通过数值分析的方法得出了利 用菲索干涉仪精密测长的相移步长的优化取值范围和干涉光束最佳初相位差的范围；对余弦 依赖算法所引起的光强误差分别就四步法、五步法得出了不同的依赖关系；并对多光束干涉 算法中几种主要的误差来源进行了不确定度评估. 关键词： 相移算法 多光束干涉 精密测长 不确定度     

Coherent optical measurement techniques in profilometric determination of local mass transfer coefficients

Some measurement techniques using a coherent light source in profilometric determination of local mass transfer coefficients are described in this paper. Different optical setups for holographic interferometry coupled with the two basic profilometric techniques: the swollen polymer technique and the sublimation technique, are described in detail. Finally, the application of electronic speckle pattern interferometry to profilometric measurements is also discussed.     

无衍射特殊光束的产生与三维表征

无衍射光束(如贝塞尔光束、艾里光束)因具有无衍射、自愈合的特性, 在很多领域都有广泛的应用. 本文提出使用纯相位型空间光调制器对光场的复振幅进行调控, 从而可以产生多种复杂模式的无衍射光束, 如强度可独立调控的多个零阶贝塞尔光束, 两个高阶贝塞尔光束干涉生成的花瓣状无衍射光束, 具有多个主瓣的加速光束等特殊的无衍射光束. 通过在待测焦场附近放置一个平面反射镜, 使其沿光轴快速扫描光场, 并由数字相机同步拍摄反射回来的一系列二维光场强度分布信息, 可实现对无衍射光束三维光场强度分布的快速测量和表征. 本实验方法和技术可以快速产生各种复杂的特殊光场并获得其精确的三维可视化重建效果, 在光学显微、光学俘获、光学微加工等领域有潜在的应用价值.     

相干贝塞尔光产生具有塔尔博特效应的局域空心光束

提出一种由轴棱锥产生的贝塞尔光干涉整形得到具有自成像塔尔博特效应的近似无衍射局域空心光束的新方法。详细分析了两束相干同频率贝塞尔光的相互作用原理及其如何控制局域空心光束的空间尺寸。数值模拟了干涉叠加后光场沿传输距离变化的光强分布及一个完整周期内光强的演变和局域空心光束的形成过程,给出了相干贝塞尔光产生局域空心光束的个数及局域空心光束最大无衍射距离的表达式。     

Numerical analysis of one-shot full-range FD-OCT system based on orthogonally polarized light

Full-range Fourier domain optical coherence tomography (FD-OCT) is generally achieved using a phase shifting algorithm. A novel design is presented for a one-shot full-range Fourier domain optical coherence tomography (FD-OCT) system utilizing orthogonally polarized light. The phase-shifted interferograms required to reconstruct the sample structure are obtained using an apochromatic quarter-wave retarder rather than a mechanical scanning operation, and thus the imaging results are free of vibrational-induced errors. The numerical analysis shows that it enhances the quality of high resolution FD-OCT and reduces the acquisition time. Moreover, the simulation results show that the proposed system is robust toward both the presence of noise in the power spectrum of the super luminescent diode (SLD) and a slight non-orthogonality of the two light beams incident on the spectrum analyzers, respectively.     

Fabrication of large-area 3D photonic crystals using a holographic optical element

A holographic technique for fabricating 3D photonic crystal is presented. The key element in the fabrication system is a holographic optical element (HOE) consisting of three gratings. Used in combination with a mask, the HOE can generate four beams under single illuminating beam, and 3D lattice structures can be formed by the interference of the four beams. Holographic approach is used to make HOE, so large area lattice structures can be fabricated. Numerical simulations indicate that beam intensity ratio of central beam to outer beam is one of the factors that affects the structures fabricated in photoresist, and high diffraction efficiency of the gratings in HOE is favorable when using cw laser with relatively low power as light source. Experimental results show clear 3D lattice structures fabricated using the HOE, verifying the effectiveness of the technique.     

相移法获取三维光弹特征相位差的方法

对于三维光弹模型,次主应力及其方向沿入射光连续变化,根据光学等效的原理,可以将三维光弹模型等效为一个包含线性相位延迟器和旋光器的光学模型。在集成光弹法中,对于每一个测量点,研究者必需通过实验获取三个特征参数。提出了一种用于确定集成光弹中全场特征相位差的五步相移法,给出了偏振光场中元器件的设置方法,并运用Jones算子推导出相移法得出的光强公式。最后使用斜射法对径向受压圆盘进行实验,验证了方法的有效性。     

用于实现散射介质中时间反演的数字相位共轭的相干性

抑制散射介质对光的散射,调控光在散射介质中的传输,是光通信、生物光子学、光镊等领域的重要课题.设计并实现了基于宽谱光源和数字相位共轭的可调控光在散射介质中传输的时间反演实验系统.实验获取了不同相干长度下物光和参考光束之间的光程差与干涉图样、相位图及时间反演信号之间的关系,分析了光源相干性对调控光在散射介质中传输的影响.实验结果表明,基于宽谱光源的相干特性和数字相位共轭技术,通过调节光程差能选择性获取同一散射角度及相同传输路径的光束的相对相位,再利用空间光调制器对参考光束进行调控,实现光束的反向传播,从而选择性实现对同一散射角度及相同传输路径的光的时间反演.     

Optical waveguide effect of thermally tampered sheet and plate glasses—application to surface stress measurements

Sheet and plate glasses have refractive index inhomogeneity parallel with their surfaces. Refractive index maxima near the surfaces behave as optical waveguides. Light waves can be excited in the guides from outside and can be extracted non-destructively, using the technique popular in optical integrated circuits. Stress birefringence, caused by surface stress in thermally tempered glasses, gives different effective indices for two linearly polarized light beams which vibrate in directions vertical to and in parallel with the surfaces. Effective index observation by two polarized light beams allows non-destructive surface stress determination.     

Estimating topological charge of propagating vortex from single-shot non-imaged speckle

Encoding information using the topological charge of vortex beams has been proposed for optical communications. The conservation of the topological charge on propagation and the detection of the topological charge by a receiver are significant in these applications and have been well established in free-space. However, when vortex beams enter a diffuser,the wavefront is distorted, leading to a challenge in the conservation and detection of the topological charge. Here, we present a technique to measure the value of the topological charge of a vortex beam obscured in the randomly scattered light. The results of the numerical simulations and experiments are presented and are in good agreement. In particular, only a single-shot measurement is required to detect the topological charge of vortex beams, indicating that the method is applicable to a dynamic diffuser.     

Analysis of low intensity square wave modulated light beams by measuring the Laplace or squared cosine transform of the time-interval probability

In this paper we study the possibility of analyzing a low-intensity light signal modulated by a square wave by measuring the Laplace or the squared cosine transform of the time interval probability. The error in the determination of the period of the signal is studied and compared with that obtained from the correlation function g⁽²⁾ (τ). We conclude that measurement of the squared cosine transform is a more advantageous method than measurement of g⁽²⁾ (τ) for low intensity light beams, the advantage increasing as the intensity of the light beam decreases. This technique can, for instance, be applied to the fields of laser Doppler velocimetry and optical communications.     

Pixel size and pitch measurements of liquid crystal spatial light modulator by optical diffraction

We present a simple technique for the determination of pixel size and pitch of liquid crystal (LC) based spatial light modulator (SLM). The proposed method is based on optical diffraction from pixelated LC panel that has been modeled as a two-dimensional array of rectangular apertures. A novel yet simple, two-plane measurement technique is implemented to circumvent the difficulty in absolute distance measurement. Experimental results are presented for electrically addressed twisted nematic LC-SLM removed from the display projector.     

测量原子里德堡态的新方法——双光子共振非简并四波混频

本文介绍了一种测量原子里德堡态的新方法--具有中间态的双光子共振非简并四波混频,与现代实验方法不同,该方法是纯光学的方法,其光路简单,检测的是相干光,而不是电子或离子信号.当用窄带宽的激光时,该技术对里德堡能级的窄光谱结构可以获得消多普勒的分辨率.     

Interference comparative analysis of the shape of wavefronts of incoherent light beams

A technique of interference comparative analysis of the shape of wavefronts that can be applied to incoherent light beams is proposed. The difference in the shape of the wavefronts of the incoherent light beams under study is visualized by using the moire pattern appearing upon superposition in real time of the lateralshear interferograms or their photographs. The possibility of producing the interference pattern that visualizes the difference in the shape of the wavefronts of incoherent beams with an enhanced measurement sensitivity is shown. The results of experimental testing of this technique in visualization of the difference between the shapes of the wavefronts of two light beams emitted by different lasers are presented.     

Chaotic Walking of Cold Atoms in a 2D Optical Lattice

Journal of Experimental and Theoretical Physics - Coherent dynamics of cold atoms in a 2D optical lattice with interfering laser beams is studied with account for internal and external degrees of...     

Error analysis for a Mach-Zehnder type speckle interferometer

A phase shifting speckle interferometer based on a Mach-Zehnder geometry is presented. The displacement field is measured using an electro-optic phase shifting technique. An analytical investigation of the accuracy of the interferometer is performed by considering the most contributing error sources. It is shown that in the case of the use of a low power laser source, the geometrical aberration of the optical component is the main contribution to the systematic errors. The case of the sampling of a full measurement is investigated. It is demonstrated that the systematic error of the full measurement has the same statistics as those given by a simple acquisition. Experimental results are reported in the case of the measurement of the deformation of industrial connectors submitted to a crushing test. It is found that for a peak to valley of 32 μm, the trueness of the measurement appears higher than 160 nm.     

Digital speckle pattern interferometry (DSPI) with increased sensitivity: Use of spatial phase shifting

This paper presents a real-time digital speckle pattern interferometry system with twofold increase in sensitivity for the measurement of in-plane displacement and first order derivative of out-of-plane displacement (slope). Spatial phase shifting technique has been used for quantitative fringe analysis. The system employs a double aperture arrangement in front of the imaging system that introduces spatial carrier fringes within the speckle for spatial phase shifting. For in-plane displacement measurement, the scattered fields from the object are collected independently along the direction of illumination beams, and combined at the image plane. For slope measurement, a shear is introduced between the two scattered fields. Experimental results on an edge clamped circular plate subjected to in-plane rotation for in-plane displacement measurement and central loading for slope measurement are presented.     

Micro-vibration model and parameter estimation method of a reaction wheel assembly

Reaction wheel assemblies (RWAs) are a source of disturbance in satellites, and they are regarded as the largest jitter contributor in optical payloads. In order to ensure a stringent jitter requirement, the wheel disturbance effects on spacecraft should be predicted precisely prior to launch through analytical or experimental approaches. For this purpose, the wheel disturbance should be identified and modeled accurately. In the present study, a micro-vibration model of the RWA is introduced through coupling an analytical wheel model and an empirical disturbance model; furthermore, a parameter estimation process of the coupled model from the micro-vibration disturbance data is proposed. In order to verify the modeling and estimation techniques, a micro-vibration model of a numerical RWA is established and its estimation error is validated. Then, the micro-vibration model is extended to consider an axial disturbance and a measurement offset effect. Finally, the micro-vibration model is applied to a commercial RWA and the model parameters are extracted from the disturbance test data of the RWA using the parameter estimation process. The analytical and experimental results demonstrate that the proposed micro-vibration model and parameter estimation process are effective in the dynamic disturbance modeling of RWAs.     

数字图像技术的数字滤光方法在图像测温中的应用

针对在比色测温法中由CCD光谱响应带宽引起的误差,提出了数字滤光的误差校正方法。该方法利用数字图像技术将光谱曲线离散化,采用离散化数据模型展开比色测温计算,在540±10nm绿光段和640±10nm红光段分别加入数字滤光算法,测温误差与外光路搭载滤光片效果接近。该方法简单实用,精度较高,在无外置滤光光路情况下实现了彩色CCD摄像设备的辐射测温,可为图像测温产品的便携性和适用化带来便利。