用散斑干涉光谱分布检测瞬态温度

为了提高对瞬态温度检测的灵敏度,提出了基于散斑干涉条纹光谱分析的瞬态温度反演算法.系统利用散斑干涉形成干涉条纹,由于瞬态温度的变化会使材料应变,从而使散斑干涉条纹改变.被测表面形变前后获得的干涉条纹由面阵 CCD 采集,其对应的光谱密度分布函数也会发生相应的改变,即由散斑干涉条纹反演得到的中心波长振幅发生改变.通过对两次中心波长幅值的比值的检测和计算,即可获得被测的瞬态温度.在分析计算了瞬态温度变化与材料应变、材料应变与干涉条纹变化的函数关系的基础上,推导了瞬态温度变化与干涉条纹振幅及相位函数关系.实验采用660 nm 半导体激光器,SI6600型面阵 CCD 探测器,从获得的光谱分布函数中提取中心波长处幅值比值,通过计算和标定,最终温度检测精度可达到±2℃.相比传统的直接检测干涉条纹的变化量,由被测面形变量推导温度的方法精度提高了近一个数量级,其精度更高、检测均匀性更好、稳定性更好.     

Adaptive correction to the speckle correlation fringes by using a twisted-nematic liquid-crystal display

An innovative technique for reducing speckle noise and improving the intensity profile of the speckle correlation fringes is presented. The method is based on reducing the range of the modulation intensity values of the speckle interference pattern. After the fringe pattern is corrected adaptively at each pixel, a simple morphological filtering of the fringes is sufficient to obtain smoothed fringes. The concept is presented both analytically and by simulation by using computer-generated speckle patterns. The experimental verification is performed by using an amplitude-only spatial light modulator (SLM) in a conventional electronic speckle pattern interferometry setup. The optical arrangement for tuning a commercially available LCD array for amplitude-only behavior is described. The method of feedback to the LCD SLM to modulate the intensity of the reference beam in order to reduce the modulation intensity values is explained, and the resulting fringe pattern and increase in the signal-to-noise ratio are discussed.     

Measuring the refractive indices of liquids with a capillary tube interferometer

A theoretical analysis of the fringe pattern produced by a capillary tube interferometer is presented, which is expected to be two-beam interference, and a computer program to simulate the interference fringe pattern is established. By comparing the simulated fringe pattern and the experimental fringe pattern, the refractive index of the liquid can be given when the two fringes coincide best. The results of this method are close to those of the Abbe refractometer.     

Analysis of capillary interferometry for measuring refractive indices of minute samples

A method of measuring the refractive indices of minute samples by analyzing capillary interferometry is introduced. With the interference theory of light, the intensity distribution of an interference fringe pattern formed by a cylindrical tube of a capillary is obtained, and the influence of some parameters on the fringes are discussed. The measurement accuracy and its relative problems are analyzed.     

Study on the quality of interference fringes from a pulsed UV source for application in a biprism based fiber Bragg grating writing

This paper presents a study on the quality of interference fringes formed from a pulsed UV (255 nm, 5.6 kHz, and 40 ns) source for an application in writing fiber Bragg gratings (FBGs). The interference fringes of separation of about 8 microm, formed by a biprism of apex angle 2 degrees , were studied for their contrast, evolution of contrast, and positional and intensity stability over a period of 5 min (over 10(6) pulses). Second harmonic UV (255 nm) sources of different spatial coherence and pointing stability characteristics were employed as the inputs. It is established that the UV fringes contrast and interference pattern stability with time is largely controlled by the optical resonator geometry of the fundamental wavelength (510 nm) copper vapor laser (CVL) oscillator. In particular, the generalized diffraction filtered resonator (GDFR) CVL produced the highest quality second harmonic beam with the highest fringes contrast and stability. The implications of these results were studied by employing these UV sources for the fabrication of the C-band FBGs by a 24 degrees apex angle biprism.     

Determining small angles of beam splitter rotation in optical vortex shearing interferometer

It is suggested to use a singular beam of unit topological charge in a scheme of vortex shearing interferometer intended for the observation of isoclinic fringes. In the interference pattern, the regions of fringe splitting determine the localization of wavefront dislocations and exhibit a shift that depends on the beam splitter rotation angel. Using the proposed method, it is possible to evaluate small angles of beam splitter rotation with an accuracy determined by the interference fringe width.     

一种基于Matlab的干涉条纹自动处理方法

对接触式干涉仪量块检定时产生的两种干涉条纹进行了研究,图像整体采用傅里叶级数曲线拟合法,实现干涉暗条纹大致定位.局部采用最小二乘二次曲线拟合法,确定干涉暗条纹中心的精确位置及暗条纹个数.利用Matlab和VC平台进行编程,快速有效地实现了干涉条纹中心位置的自动判读. 该方法已应用在中国计量科学研究院接触式干涉仪的量块检定中.     

干涉条纹快速预处理的新方法

介绍一种基于数学形态学的新方法以实现干涉条纹的快速预处理（去噪声、细化条纹等），该方法所采用的光学系统结构简单，具有图像处理的快速并行性。用它处理了三种干涉条纹，获得了很好的处理效果。     

Optical fringe multiplication in moiré interferometry

An optical method for multiplication of moiré fringes is proposed to increase the sensitivity of moireé interferometry. The process involves two recording steps. In the first step, a traditional moiré interferometry setup is used. The moiré pattern containing carrier fringes and load fringes is recorded onto a glass-based holographic plate. The carrier frequency is much lower than that of the original specimen grating. The plate is then developed. In the second step, the holographic plate, regarded as a distorted specimen grating, is further examined by a similar moiré interferometry system. The frequency of the second virtual grating is arranged to be 2n times that of the carrier fringes contained in the recorded plate. As a result, the load fringes are revealed with a multiplication factor of 2n. The interpretation of the optical multiplication method from wave-front interference theory is given and an experiment is conducted.     

Generation of carrier fringes in holography and shearography

Double-exposure holography and double-exposure shearography are often used together with the carrier fringe technique, which requires additional shifting of the light source in a prescribed manner between exposures. In the holographic carrier fringe technique, difficulty in prescribing a suitable movement of the light source may be alleviated through visualization of the moiré fringes that are reconstructed by slight displacement of two overlaid families of ellipsoids in a holodiagram. Because shearography is the first differential of holography, it is often impractical to perform two successive optical differentiations on the ellipsoids to visualize the shearographic carrier fringes. A simple method of discerning holographic and shearographic carrier fringes is described. The method is based on the hyperboloids in a holodiagram that represent Young's (interference) fringes produced by the interference of two point sources. The hyperboloids are analogous to holographic carrier fringes, whereas the moiré patterns reconstructed from two overlaid hyperboloids are analogous to shearographic carrier fringes. Use of this method for explaining the formation of deformation fringes in plate bending, as well as the effect of light-source movement on the deformation fringes, is also illustrated.     

Phase retrieval in digital speckle pattern interferometry by application of two-dimensional active contours called snakes

We propose a novel approach to retrieving the phase map coded by a single closed-fringe pattern in digital speckle pattern interferometry, which is based on the estimation of the local sign of the quadrature component. We obtain the estimate by calculating the local orientation of the fringes that have previously been denoised by a weighted smoothing spline method. We carry out the procedure of sign estimation by determining the local abrupt jumps of size pi in the orientation field of the fringes and by segmenting the regions defined by these jumps. The segmentation method is based on the application of two-dimensional active contours (snakes), with which one can also estimate absent jumps, i.e., those that cannot be detected from the local orientation of the fringes. The performance of the proposed phase-retrieval technique is evaluated for synthetic and experimental fringes and compared with the results obtained with the spiral-phase- and Fourier-transform methods.     

Compact interferometric optical tweezer for patterned trapping and manipulation of polystyrene spheres and SWCNTs

We demonstrate a simple and compact optical interferometric unit combined with a conventional optical tweezer system for simultaneous multiple trapping and micromanipulation of mono-dispersed polystyrene spheres and aggregation of small-floating clusters of single-walled carbon nanotubes (SWCNTs). The interferometric unit was made compact by means of coating a thin layer of aluminum oxide on one side of the cubic beam splitter (CBS) which works as a static reference mirror and an adjustable mirror was mounted on a XYZ translational stage facing the other adjacent side of the CBS. Thus, the developed interferometric unit is quite analogous to a Michelson interferometer but is compact. Sinusoidal interference fringes with variable carrier frequency and orientations were generated. The interference fringes were then used for multiple trapping of polystyrene spheres along bright fringes resulting in pattern formation and also the aggregation of tiny floating clusters of SWCNTs. The proposed system is compact and easy to align because of its common-path geometry.     

Approach for the evaluation of speckle deformation measurements by application of the wavelet transformation

We introduce a new, to our knowledge, method using wavelets and probability theory for the evaluation of speckle interference patterns for quantitative out-of-plane deformation measurements of rough surfaces of nontransparent solids. The experiment uses a conventional Twyman-Green interferometer setup. The speckle interference patterns are obtained by the common method of subtraction of images taken before and after a surface deformation. The data are processed by a wavelet transformation, which analyzes the image structures on different length scales. Thus it is possible to separate the interference fringes from the noise. From the locations of the interference fringes, the deformation of the surface can be reconstructed by means of probability theory.     

平晶检定时干涉条纹的快速调整方法与平面度计算

在平面等厚干涉仪上检定平晶工作面平面度时,需要在被检区域调整出3到5条干涉条纹,依据测量原理和计算公式求出被检平晶工作面的平面度.文章重点分析干涉条纹的快速调整方法与标准平晶平面度的正确引用方法.     

Study of adaptive elliptical ideal low-pass filters used for denoising of digital speckle interferograms obtained in phase-shifting digital speckle pattern interferometry

Ideal low-pass filtering methods were studied in detail and adaptive elliptical ideal low-pass filters proposed for the first time. The proposed adaptive elliptical ideal low-pass filters can be used effectively for denoising of digital speckle interferograms obtained in phase-shifting digital speckle pattern interferometry. The shape of adaptive elliptical ideal low-pass filters is determined according to the spectrum distribution of interference fringes by using the adaptive method. Theoretical analysis, simulation calculation, and experimental results are presented, and are in good agreement.     

Interference of Three Electron Waves and Its Application to Direct Visualization of Electric Fields

We present a method for the interference of three electron waves and its application to direct visualization of pure-phase objects such as electromagnetic microfields. Using a transmission electron microscope equipped with a field-emission electron gun and two electron biprisms, an object wave and two reference waves at either side of the object wave are superposed to produce a new type of interference pattern. In this pattern, equal-phase lines of the object wave are directly displayed as intensity modulation of periodic interference fringes. An electric field around a latex particle, induced by electron-beam irradiation, has been observed. The electric charge of the particle is estimated, from an observed phase shift, to be 6.4 × 10⁻¹⁷C, which is equal to about 400 electrons. A change of the electric field around charged alumina particles at high temperatures has been observed dynamically.     

Fluorescence correlation spectroscopy with patterned photoexcitation for measuring solution diffusion coefficients of robust fluorophores

Patterned fluorescence correlation spectroscopy is developed as a new technique for measuring diffusion coefficients of photostable fluorescent probe molecules. In this method, interference between two intersecting, coherent laser beams creates an excitation fringe pattern from which fluorescence emission is monitored. Spontaneous concentration fluctuations of fluorescent molecules within the excitation volume are detected as excess noise on a fluorescence transient; concentration fluctuations are driven primarily by diffusion of these molecules between interference fringes although contributions from photobleaching and diffusion over the entire pattern dimensions can also be observed. Autocorrelation of the fluorescence transient allows analysis of the temporal characteristics of the fluctuations, which were used to determine solution diffusion coefficients; the method was applied to study the diffusion of Rhodamine 6G (R6G) in water/methanol solutions containing added electrolyte and in pure ethanol. The method can be used to characterize the diffusive transport of fluorescently labeled species, which is an important issue in designing small-volume detection experiments.     

Far-field interference from a sphere and its applications

A theoretical model of far-field interference from a sphere has been established, and its applications have been investigated. When two coherent parallel laser beams shine on a smooth sphere surface from opposite directions, the reflected lights form interference fringes at far field. The fringes have hyperbolic shapes and are not uniformly distributed. This paper derives a method for calculating the path-length difference between two parallel reflected lights, analyzes the interference field, and discusses reasons that cause the fringe density variations. A formula for calculating the highest orders of interference fringes is also provided. A method for using a spectrometer, CCD camera, and computer to measure the sphere diameter is demonstrated. The results agree with those from an Abbe comparator. The theory and methods are also suitable for measuring diameters of smooth cylinders.     

Theory of Ultra-high-resolution Optical Raman Ramsey Spectroscopy

A non-perturbative theoretical analysis of Ramsey interference lineshapes in three-level lambda systems excited by laser fields has been developed for the general case of several interaction regions. In conventional Ramsey excitation, two laser fields excite the lambda system each in two separate spatial interaction regions. Here we examine how increasing the number of interaction regions or altering the interaction times change and improve the lineshape characteristics such as fringe visibility. For short interaction times the fringe pattern is strongly dependent on the number of interaction regions, with the n = 2 sinusoidal fringes replaced by sharper fringes of greater visibility. With larger interaction times, the fringe pattern is virtually unchanged on increasing the number of interaction regions. The optimum fringe pattern is obtained with short interaction times and a larger (n a 9) number of regions.     

Strange interference blots in the interferometry of inhomogeneous birefringent objects

We show both experimentally and by numerical simulation that in the polarization interferometry of inhomogeneous birefringent objects, besides the usual interference fringes, interference blots may appear. In a light-field circular polariscope, interference blots are dark areas that may expand through a number of interference fringes. In a dark-field circular polariscope, interference blots are bright. In the vicinity of the interference blots interference fringes are deformed and their bifurcation may occur. It is shown that the cause of the interference blots is rotation of the principal birefringence axes.