Evaluation of photographic emulsions using speckle patterns

This communication reports the observation of a typical set of fringes in transmission, when a wet processed photographic plate, exposed to laser speckles and kept tilted with respect to normal, isscanned by a thin laser beam. A possible explanation for the fringe formation is given which is based on the speckle stretching due to swelling of the emulsion. A method has been proposed to estimate emulsion swelling due to wet processing and the rate of its shrinkage during subsequent drying process. Experimental results are presented for Kodak 649-F spectroscopic plates.     

Optical velocimetry: a method using two shifted speckle patterns

A new optical method for measuring the lateral velocity of a diffuse object is presented. The speckle pattern, originated by the surface under coherent illumination, is imaged into a linear photodiode array. The scanning time of the array is selected to detect two slightly shifted speckle patterns. By processing the intensity distributions, the velocity of the surface is derived. Some experimental results are shown.     

Correlation of speckle patterns generated by laser point source — Illuminated diffusers

In this paper it is shown that, when a ground-glass transilluminated by a diverging or converging beam is axially translated, there exists a particular plane in which the corresponding speckle pattern remains correlated. Consequently, under some experimental conditions on this incident beam and the geometry of the optical setup, a speckle pattern generated by a set of two parallel ground-glasses suffers no decorrelation when one of them is axially or laterally translated.     

The simulation of the origin and propagation of speckle field generated through a plane wave and Gaussian beam and its verification by speckle correlation method

This paper presents a simulation model of the origin and propagation of speckle field within the Fresnel approximation and verification of the model through a speckle correlation method for determination of in-plane object's translation. There is used a convolution form of the Fresnel–Kirchhoff diffraction integral in the simulation model instead of often used Fast Fourier Transform approach. A possible way of simulation of the light scattering by object's surface and in-plane translation of the illuminated surface is mentioned, whereas two types of illumination (plane wave and Gaussian beam) are used. Finally, results of numerical correlation of generated displaced speckle fields are shown and compared with the results obtained by theoretical relations.     

平面透射光栅的菲涅耳衍射

从标量场的菲涅耳衍射理论出发,研究了球面波入射平面透射光栅的衍射场,导出菲涅耳衍射场的复振幅分布,并得到光栅菲涅耳衍射角的计算公式．结果表明,在理想情况下菲涅耳衍射的每一级衍射波都是一个球面波;在对菲涅耳衍射角进行新的定义后,衍射角的计算仍然可以采用夫琅禾费衍射的光栅方程．     

Partially coherent Fresnel diffraction by a slit aperture. III. Fresnel diffraction patterns

The intensity distribution in the Fresnel diffraction pattern of a slit aperture illuminated with partially coherent light is obtained, as a function of the coherence condition across the aperture, by evaluating the formula developed in a previous paper. It is shown that the Fresnel diffraction pattern is affected by the coherence condition of illumination across the aperture and its form.     

The autocorrelation function of polychromatic laser speckle patterns near the image plane

The autocorrelation function of polychromatic speckle patterns produced near the image plane of a double diffraction imaging system is experimentally studied. The condition under which the polychromatic speckle field obeys Gaussian statistics is further investigated as a function of the numberN of scattering cells, using the average contrast of the speckle intensity fluctuations. The profile of the autocorrelation function is next investigated as a function ofN and the defocused distance from the image plane. It is found that the average contrast and autocorrelation function of the polychromatic speckle intensity fluctuations converge less rapidly with an increase inN than those of the monochromatic ones.     

Fluctuations of the fringe pattern generated by a partially developed speckle

The fluctuations of fringe pattern intensity are studied experimentally by means of Young's interference experiment. It is shown that the average contrast of the fringe intensity changes with the position in the fringe pattern. The characteristic values of the contrast are measured as a function of the separation of the pinholes. The experimental results are discussed qualitatively.     

弱散射体产生的菲涅耳极深区散斑场相位涡旋演化的实验研究

实验提取了弱散射体产生的菲涅耳极深区的散斑场.发现当散射距离一定时,弱散射体光场的相位分布特征随散射体的粗糙度的变化而变化;对于某一弱散射体,相位分布特征随散射距离的变化而变化;当弱散射体的粗糙度大到一定程度时,才产生相位涡旋现象;散射体表面上存在相位涡旋;弱散射体产生的相位涡旋的密度随散射屏粗糙度的增大而增大,还随散射距离的增大而增大.研究结果对于认识弱散射体的相位及相位涡旋分布特征随粗糙度和散射距离的演化具有重要意义,而且对于认识散斑场随散射距离的演化有一定的帮助.     

Encryption and decryption using a sandwich phase diffuser made by using two speckle patterns and placed in the Fourier plane: Simulation results

In the present paper, we describe the encryption and decryption of two-dimensional images. The encryption is done by employing a sandwich phase diffuser made by using two elongated speckle patterns, and placed in the Fourier plane of a double random phase encoding system. After encryption, the two constituent phase diffusers of such a sandwich diffuser are separated. During decryption, if the conjugate of either of the two elongated phase speckle patterns is used, the image cannot be retrieved. Correct decryption is also not possible if a sandwich diffuser with any of the phase speckle patterns is shifted in position with respect to the other. For decryption, the encrypted image is Fourier transformed and multiplied by the conjugate of the sandwich diffuser, and then the product is further Fourier transformed. It is possible to generate the image only if both the elongated phase speckle patterns are matched point-to-point and then the proper conjugate is made. The use of elongated speckle patterns in constituting a sandwich phase diffuser makes the system less complicated as compared to the use of a sandwich diffuser made with normal speckle patterns, enabling an easy alignment of the random phase diffuser at the time of rejoining the constituent diffusers for making the right key. The ease of alignment is due to the reduction of the requirement of 360° scanning at the time of rejoining these diffusers with little reduction in the security of the system. Simulation results are presented in support of the proposed idea. For optical implementation, the decrypted image may be obtained by generating a phase conjugate wave by the phase conjugation technique, and passing through the same sandwich phase diffuser. To evaluate the reliability of the technique, mean square error (MSE) between the decrypted and original image has been calculated.     

Intensity and phase distribution in deep Fresnel diffraction region generated by multi-pinhole aperture

The Kirchhoff diffraction theory is applied to the multi-pinhole aperture diffraction screens, and the intensity, the zero-contour of the real and imaginary parts of complex amplitude and the phase distribution in deep Fresnel diffraction region are simulated. It is found that the number of bright spots, the zero-contours of the real and imaginary parts of complex amplitude and the phase singularities are all related to number of pinholes in diffraction screens. The brightness of bright spots in center of each pattern would become larger with increasing number of pinholes. In addition, there are many lines, on which the intensity value is close to 0.     

Phase extraction in speckle interferometry by a circle fitting procedure in the complex plane

In speckle interferometry (SI), temporal signals are amplitude- and frequency-modulated signals and exhibit a fluctuating background. Prior to phase computation, this background intensity must be eliminated. Here our approach is to build a complex signal from the raw one and to fit a circle through the points cloud representing its sampled values in the complex plane. The circle fit is computed from a set of points whose length is locally adapted to the signal. This procedure-new to our knowledge in SI-yields the background and the modulation depth and leads to the determination of the instantaneous frequency. The method, applied to simulated and experimental signals, is compared to empirical mode decomposition (EMD). It shows great robustness in the computation of the sought quantities in SI, especially with signals close to the critical sampling or, on the contrary, highly oversampled, situations where the background elimination by EMD is the most prone to errors.     

固体表面菲涅尔阵列产生的声束聚焦的研究

在固体表面上菲涅尔阵列可实现聚焦声束的B扫描。此阵列产生的弹性波场的分析是固体中会聚声束B扫描成像的物理基础.给出此聚焦声场的全面分析,包括:纵波和横波会聚声束的频率扫描特性;纵波声场沿对称轴和在焦面上的分布;在主焦点的频率响应;纵波场的全空间分布以及阵列参数对会聚声场的影响.最后还讨论了横波的分布.     

Form of Fringes of an Interference Pattern Localized in the Plane of a Double-Exposure Fresnel Hologram for Wave-Front Control

Russian Physics Journal -     

Field generated by an anisotropic conducting plane in a half-space with chiral properties

This article inaugurates theoretical studies on a new class of composite structures that are a combination of anisotropically conducting surfaces and media possessing chiral properties. To test the mathematics, we solved the simplest model of the problem in which an in-phase electric current filament excites a plane formed by a layer of straight conductors at the interface of two isotropic media, one of which is chiral. The solution is given as a Fourier integral. As shown by analysis, one retarded wave of a discrete spectrum and three waves of a continuous spectrum are excited in the given structure. The first one exists only because of the anisotropically conducting plane and does not exist without it, while the latter three are associated with plane waves of corresponding homogeneous media, magnetodielectric and chiral.V. D. Kuznetsov Siberian Physicotechnical Institute, Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 34–38, September, 1994.     

微粗糙圆柱的各向异性散斑特性研究

分析了高斯光束照射微粗糙圆柱在菲涅尔衍射区形成的散斑图像统计特性,给出了强度起伏自相关函数与表面曲率及粗糙程度等参数之间的关系.根据强度起伏自相关函数的离散化定义,实验并计算了圆柱轴向与径向结构有差异情况下的散斑强度起伏相关函数.结果表明,对于C1和C2圆柱沿垂直于圆柱轴向的散斑尺寸变长,强度起伏自相关函数沿平行和垂直于圆柱轴两个方向的波动相差较大;对于C3和C4圆柱两个方向上的散射特性基本相同;测量C1和C3的结果表明,散斑尺寸和形状依赖于圆柱表面的皱褶和圆柱表面曲率两个因素.研究结果对于如柱型管道、轴承等方面的机械制造的质量控制有重要的应用价值.     

3D Reconstruction of Large-Depth Objects Using Fresnel Diffraction of a Ronchi Grating and Simultaneous Recording of Reference and Object Fringes

We propose an active triangulation based range-finding system that, besides its simplicity, has two advantages over similar existing systems. First, the system can acquire range data for large-depth objects since it generates an illumination pattern with large-depth of focus using Fresnel diffraction from a Ronchi grating projected over the entire object surface. Secondly, the system does not need preliminary recording of reference fringes since it displays simultaneously, on a single image, both reference and object deformed fringes. This system offers other properties: it is mechanically simple, uses everyday optical components, is low cost, can be operated via a PC and uses relatively simple image analysis software. Three dimensional reconstructions are illustrated for various objects having 10 cm maximum depth variations. The depth accuracy (typically 0.5 mm for an object located at 350 mm from the camera) is comparable with other systems, but a certain compromise has to be accepted in acquisition time (typically 1 minute). This system can find applications in research laboratories as a tool to provide range data with relatively good depth accuracy.     

Sound generated by vortices in the presence of a porous half-cylinder mounted on a rigid plane

The sound generated by a single vortex and by two identical vortices in the presence of a half-cylinder made of porous material mounted on a rigid horizontal plane is studied theoretically using the acoustic analogy and the matched asymptotic expansion method. Both longitudinal and transverse dipoles are observed upon the introduction of the porous cylinder, but the former is considerably stronger than the latter in all the cases studied. Results suggest that the amplitudes of the dipoles and the overall acoustical energy radiated can be higher than that in the rigid cylinder case under some suitable combinations of flow parameters, especially when the flow resistance inside the porous material seen by the vortices is very small.