Speckle shear interferometry

A number of speckle shear methods and their applications to ndt are discussed. Experiments using multiple apertures with custom-made optical elements have shown that in-plane displacement, slope and curvature patterns can be obtained by filtering through appropriate haloes.     

Speckle interferometry of phase-modulated beams

It is shown experimentally that a scatterer placed in the interference field of the signal and the reference beams can be used for detecting phase-modulated optical signals. The signal observed in this case is formed by the space-time modulation of the speckle structure of the beams. The influence of the geometry of the interferometer and the amplitude of phase modulation on the parameters of the output signal is considered.     

Speckle photography combined with speckle interferometry

By combining speckle interferometry (SI) measurements with speckle photography, the fringe visibility can be kept high despite the presence of a large bulk or rotating motion of the object. This combined technique improves the usability and measuring range of both pulsed and phase-stepped SI-methods. This paper reviews the theory of fringe formation in SI and shows some recent applications of this combined technique.     

Speckle interferometry for measurement of continuous deformations

Improvements of a method for measurement of continuous displacements and deformations with digital phase shifting speckle pattern interferometry are presented. The method is based on an algorithm that, with the knowledge of the initial phase, only needs one image at a time to evaluate continuos phase changes due to object deformations. In the improved method, the initial random phase of the speckle pattern is evaluated using a number of phase-shifted images before the deformation under study. This is used for increasing the accuracy of the initial phase estimation and reducing influences from image noise and other measurement disturbances. The phase-shifted speckle patterns are used as references for comparison with the speckle patterns of the deformed object, thereby increasing the reliability and accuracy of the phase estimations of the deformed patterns. The technique can be used for measuring deformations such as transients and other dynamic events, heat expansion as well as other phenomena where it is difficult to accomplish phase shifting during deformation.     

Speckle averaging in deformation analysis using video speckle interferometry

We show that speckle averaging in deformation analysis using video speckle interferometry increases the signal to noise ratio and improves the resolution in the resulting image. Speckle averaging in deformation analysis normally demands a very high degree of stability and repeatibility. Averaging phase gradient maps reduces these demands considerably. Experimentally, deformation details down to 2 × 2 pixels in the averaged pictures have been resolved.     

Speckle interferometry for the strain field of geologic structure model

Based on imitative experiment of structure mechanics,four-aperture defocusedspeckle shearing interferometry is used to obtain the distribution of strain field of the geologicstructure model of the Jiulong mountain in Sichuan Basin.And through the analysis of the ex-perimental data,we can give some experdriental basis for recognizing the distribution of thegeologic fracture in the district of the Jiulong Mountain. Exploration practice shows that fracture distribution predicted by theory agrees with actu-al situation.     

Speckle interferometry and Doppler diagnostics of microflows of scattering liquids

A relation for the correlation function of intensity fluctuations of the speckle field formed upon scattering of focused light radiation in blood flows in microvessels is obtained. The width of the intensity-fluctuation spectrum is shown to depend not only on the velocity of the flow, but also on its scattering characteristics. Simulation of the processes of scattering of light beams in random flows is performed by the Monte Carlo method. The expression for the first spectral moment of the Doppler signal is derived both on the basis of the theory of radiative-energy transfer and within the framework of the speckle-interference approach; comparison of the obtained results is carried out.     

Speckle interferometry methods for displacement and strain measurements using photorefractive crystal

Photorefractive crystals offer several attractive features such as high resolution and in situ processing. As the images are erasable, these crystals are suitable for read–write applications and hence find potential use in speckle photography, image processing and holography. The barium titanate (BaTiO₃) crystal as recording medium has been extensively used as a novelty filter for real-time in-plane displacement measurements employing two-beam coupling configuration. This paper presents new optical configurations in speckle shear photography to measure in-plan displacement and the strain in real time using BaTiO₃ crystal as recording medium. Speckle photography studies are made using a simple two-beam coupling configuration. In speckle shear photography, a diffused object illuminated with two parallel narrow laser beams is imaged inside the crystal, and a pump beam is added at this plane. The speckle patterns due to each beam and the pump beam produce index gratings. When the object is deformed, the speckle patterns shift consequently. We now have four speckle fields: two generated from the interaction of pump beam with the index gratings and two pertaining to deformed states directly transmitted through the crystal. Thus, the fields from respective points on the object interfere after passage through the crystal and produce the Young's fringe patterns. Due to strain, the fringes in each pattern are of different width and orientation, resulting in the generation of a Moiré pattern. The strain is obtained from the width and orientation of the fringes in the Moiré pattern. The experiments are conducted on a specimen with a notch, which is subjected to tensile loading. The in-plane displacement is measured separately in another experiment. The above studies are carried out at Nd–Yag laser.     

Speckle interferometry, fibre optic sensors and laser induced ultrasounds as solutions to industrial demands

Industrial operators have been taking interest in optical diagnostics through years. Optical methods are mainly well appreciated for their attitude to be used as non-contact and non-invasive techniques. The paper presents three examples of applications carried-out by researchers of Centro Elettrotecnico Sperimentale Italiano (CESI) in collaboration with people working in industrial fields. The first part shows the applications of speckle interferometry to measure residual stresses in association with the traditional blind-hole drilling, while the second part presents the installation of fibre optic sensors in a power plant for monitoring possible overheating to avoid fires and finally the last presentation outlines a particular application in the field of laser generated ultrasounds that is the monitoring of the variation of ultrasonic speed propagation due to residual stresses.     

Speckle interferometry through small multiple apertures: Michelson stellar interferometer and aperture synthesis in optics

The use of a Michelson stellar interferometer or multiple-hole interferometers is considered as a special case of speckle interferometry. Formulas are given for the power spectrum of the interference pattern produced by the multiple apertures. The limitation in stellar magnitude is shown to increase with the number of apertures, while it is independent of the telescope size when a large single aperture is used.     

相移干涉术及广义相移数字全息干涉术

在基础光学框架内说明了传统的相移干涉术及近年来发展的广义相移数字全息干涉术的基本原理;前者要求特殊值等步长相移,而后者则可以采用任意未知相移值.着重介绍了广义相移干涉术中的物波恢复算法,以及基于衍射场统计特性的未知相移提取算法.从一个侧面沟通了基础光学与近代光学之间的关系.     

像面散斑平均尺寸对激光散斑成像的影响

以激光散斑衬比分析为基础的激光散斑成像技术,是一种无需扫描的全场光学成像方法,在监测生理及病理状态下组织血流动态变化中的应用日益广泛.在实际应用中,像面散斑平均尺寸等多种因素影响散斑衬比值,使得该技术在反映血流变化的准确性方面受到影响.采用一种成像散斑计算机模拟方法研究了像面散斑平均尺寸对成像散斑统计特性的影响,分析了成像参数与像面散斑尺寸的定量关系,并通过物理模型实验对模拟结果进行了验证.研究结果确认了合理的像面散斑平均尺寸计算公式,证实了散斑衬比值随像面散斑平均尺寸增大而减小的现象,并为确定合理的成像参数提供了依据.     

激光散斑验光仪

本文介绍了激光散斑验光仪的验光原理,并给出了该验光仪的光学原理图,同时也给出了与Canon AutoREF R-10电脑验光仪进行验光试片比较的测试结果。     

Speckle pattern interferometer

We describe in this paper a speckle interferometer constituted by two partially diffusing plates. They are illuminated by a laser and the resulting intensity distribution is observed in the image plane of the source. Each speckle of this plane (Fourier plane) is modulated by a ring system whose interference order depends on its phase. Since the observation plane is a Fourier plane, a longitudinal or lateral shift of one of the diffusers results only into a change of the modulating fringes, the speckles themselves remaining unchanged. A photographic plate which records successively the intensity distribution lying in the Fourier plane before and after the considered shift, exhibits after processing a system of Moiré fringes, the shape of which depends on the nature of the translation given to the diffuser between the exposures.     

Programmable interferometry

The advent of automatic data-processing for interferometry greatly reduced the complexity of interferometric testing, thereby significantly increasing its usage both within and outside the optics community. A great many of these new applications require special data-processing and output data not normally used for testing lenses. To address these new measurement problems, many data-analysis programs were written, ranging from advanced analysis of wavefronts (i.e., Zernike polynominals, point-spread function, modulation-transfer function) to analysis of mechanical surfaces, such as Winchester-disk read/write heads. Some of these programs were very specific to a particular application, and some tried to be general and as such became cumbersome. Even with much of this software available for sale to the general public, most applications other than simple surface and lens measurements usually cannot be solved directly by using the available programs. In an attempt to solve this problem, we have developed software for interferometry that allows users to easily develop their own measurement routines. The solution was to take a version of the BASIC programming language and add the commands necessary to do interferometry. This software is resident in a processor that can easily be adapted to a large number of interferometry applications. By using this processor and its associated software with an appropriate interferometer, it is possible for the user to tailor the measurement to a particular application. This can be very useful in an optical-production shop, where each different testing application can have its own program. If the program is written properly, the operator will not have to set up any default conditions or format the output; the operation of the program can be reduced to the pushing of a single button, and the output will be formatted properly for that particular test. Examples of this system in actual optical shop-testing situations will be discussed.     

Kaon interferometry

2-kaon and 2-pion correlation functions for an expanding thermalized source are compared. In the Yano-Koonin-Podgoretskii parametrization of the correlation function, the HBT radius parameters are shown to obeyM _∟-scaling in the absence of collective transverse flow. This scaling is broken by transverse flow. An accurate comparison of pion and kaon correlations can thus resolve issue whether the observedM _∟-dependence of the transverse radius parameter is due to transverse collective flow or other transverse gradients. Effects from resonance decays are shortly discussed.     

Spiral interferometry

We present a surprising modification of optical interferometry. A so-called spiral phase element in the beam path of a standard microscope results in an interferogram of phase samples, for which the interference fringes have the shape of spirals instead of closed contour lines as in traditional interferograms. This configuration overrides the basic problem of interferometry, i.e., that elevations and depressions cannot be distinguished. Therefore a complete sample profile can be reconstructed from a single exposure, promising, e.g., high-speed metrology with a single laser pulse. The method is easy to implement, it does not require a spatially separated reference beam, and it is optimally stable against environmental noise.