K-distributed spatial intensity derivatives in monochromatic speckle patterns

In a monochromatic speckle pattern the spatial derivative of the intensity obeys a laplacian distribution density. When the intensity derivative is measured with a detector of finite area, the measured distribution departs from the ideal laplacian form. Exact expressions are given for the mean and the variance of the measured signal and an approximate form for the probability density is derived consisting of a K-distribution form.     

Reconstructing a complex field from a series of its near-field diffraction patterns

We propose a method for reconstructing a complex field from a series of its near-field diffraction patterns.This method is based on the paraxial Fresnel diffraction equation without making further approximations.Numerical simulations are presented showing that a complex field can even be reconstructed with moderate qualities from its two near-field diffraction patterns and almost exact reconstructions can be obtained when three or more diffraction patterns are used.We also show by numerical simulation that the correct diffraction distances can be recovered in case only coarsely measured values are available.This method may be applied to phase imaging of weak-absorption objects.     

Fourier magnitude of the field incident on a random scattering medium from spatial speckle intensity correlations

Spatial speckle intensity correlations are used to determine the spatial Fourier magnitude of a field incident on a random scattering medium. The patterned beam is scanned across the scattering medium, and the speckle pattern on the opposite side is imaged at each beam position. A theory based on a Green's function representation is used to reconstruct the spatial Fourier magnitude of the patterned incident field.     

Moments of the intensity of a non-circular Gaussian laser speckle pattern in the diffraction field

Statistics of the intensity of a non-circular Gaussian speckle field that arises in imaging and propagation geometries was analyzed in the past but no general expressions for the moments of intensity were given. In this paper general expressions for the moments of the intensity of a non-circular speckle field are derived and their dependence on the path and beam parameters is discussed.     

Relation between statistical properties of surface roughness and the averaged speckle intensity in the diffraction field

A theoretical and experimental investigation is made on the relation between the statistical properties of a rough surface and the averaged speckle intensity in the diffraction field. The theoretical analysis is performed in some detail over a wide range of the random phase variation for various illuminated objects. The result gives an interpretation for the behavior of the averaged speckle intensity obtained experimentally for various states of rough surfaces.     

Statistical properties of speckle intensity variations in the diffraction field under illumination of coherent light

The statistical properties of speckle intensity variations produced by coherent light in the diffraction field of diffusely transmitting objects are investigated experimentally with intimate relation to their surface roughness. The probability distribution and the average contrast of intensity variations in speckle patterns are studied as a function of the surface roughness of the objects and the receiving plane in the diffraction field.     

Tuning the intensity statistics of random speckle patterns

Speckle patterns are a fundamental tool in a variety of physical and optical applications. Here, we investigate a method of precisely tuning the intensity statistics of random speckle patterns into a desirable pattern that possesses the same spatial correlation length and similar statistics distribution. This tuning mechanism relies on the derivation of the transform function and transmission matrix, which achieves different contrasts while maintaining the same average value or energy level. The statistics properties of the generated speckle patterns are further investigated by analyzing the standard deviation under different fitting parameters. Precisely tuning the intensity statistics of random speckle patterns could be useful for both fundamental research and practical applications, such as microscopy, imaging, and optical manipulation.     

基于布拉格声光衍射场的光强非均匀空间分布研究

为了保证合成孔径激光雷达测试中信号光的光束质量,从波动方程出发,推导出传统的衍射光源布拉格声光作用的耦合波方程。根据测试对光束质量的不同要求,借助有限差分方法分析衍射场光强的空间三维分布,发现声场振幅的不均匀分布会影响声光衍射场的光强分布,光强分布不均造成实验中信息光源的探测难度。通过光强空间分布研究增大有效通光孔径到3 mm,解决了声光调制器光束衍射质量问题,改进后的光束质量达到实验要求。该研究方法适用于改进声光器件工作参数。     

Determination of subpixel microdisplacements of speckle structure using the phase shift of spatial spectrum field

An experimental method for measurement of subpixel microdisplacements of speckle structure based on the parameters of the linear phase shift in the field of the complex spatial spectrum of the displaced structure is proposed and experimentally implemented. The phase shift is determined when a phase shift of spectrum is numerically added and the correlation analysis of the resulting linear phase shift in the spatial spectrum of specklegrams is performed. The method provides additional possibilities in the measurements using digital speckle photography when the period of interference fringes formed in the total spatial spectrum of specklegrams is significantly greater than the spectral width.

     

Velocity measurement of the diffuse object based on time-differentiated speckle intensity fluctuations

This paper proposes a new velocity measuring method for a moving diffuse object on the basis of the autocorrelation of time-differentiated speckle intensity fluctuations. The theoretical background and experimental verification of this method are given. The correlation length of time-differentiated speckle intensity fluctuations is defined by the point at which the correlation becomes zero. By means of the correlation length the object velocity is found to be accurately measured.     

Wavelength dependence of intensity fluctuations in laser speckle patterns from biological specimens

Speckle patterns obtained when botanical specimens are illuminated with laser light are observed to fluctuate at a rate which depends on the wavelength of the light used. It is suggested that this wavelength dependence may be of value as an additional degree of freedom in some applications of intensity fluctuation spectroscopy.     

Fringe analysis and phase reconstruction from modulated intensity patterns

A novel method of determining phase from a modulated intensity pattern is described. A line integral of the gradient of the phase is used to reconstruct the phase, eliminating the necessity for complex methods of phase unwrapping. The new algorithm can be used with any technique that experimentally or theoretically yields the cosine and sine or the tangent of the phase. This phase-reconstruction process works effectively even in the regions of high-intensity gradients and is insensitive to the profile of the illuminating beams and to the shape of the domain boundaries.     

菲涅耳深区散斑强度统计特性及演化

利用直透光波和高斯散斑场的叠加理论和基尔霍夫近似研究了菲涅耳深区散斑的构成,给出了菲涅耳深区散斑场及其强度概率密度和对比度的表达式.利用原子力显微镜测量的随机散射表面高度分布数据模拟菲涅耳深区不同散射距离处散斑,并计算绘出其强度概率密度和对比度曲线.理论与模拟相结合研究这两个统计函数的特征和直透光强所占比例的影响,以及它们随散射距离的演化规律.     

用衍射屏平移相因子计算夫琅禾费衍射场强分布

用Fresnel-Kirchhoff衍射积分求解夫琅禾费衍射场分布时引入衍射屏平移相因子,可简化对较复杂衍射屏夫琅禾费衍射的讨论,加深对衍射、干涉现象的理解．     

Image multiplexing and color images with theta modulation of the speckle patterns

We describe a technique of image multiplexing which employs theta modulation of the speckle patterns using the same diffuser to modulate all the signals. This technique is applicable for binary signals. The basic advantage of this technique is that a great number of signals can be stored without cross-talk, because each area of the film is exposed only once. In addition to this, if the development film is processed with white light, color images of the signals will be retrieved.     

Partially coherent speckle patterns of weak phase plates

We examine speckle patterns created by weak diffusers in imaging systems that utilize partially coherent light. Their Wiener spectra generally emphasize low spatial frequencies more than the corresponding coherent light Wiener spectra.     

基于物体像的干涉条纹图像中散斑噪声的识别方法

散斑噪声是激光干涉时的普遍现象,其覆盖被测表面对应区域的形状信息,造成测量误差。针对斜入式激光干涉测量中散斑噪声的特点,提出一种基于物体像的散斑噪声的识别方法。该方法通过统计物体像中有效测量区域和背景区域内灰度分布的特点,自动计算出判定散斑噪声的上下阈值。基于物体像与干涉条纹图像间微米级的映射关系,得到干涉条纹图像中散斑噪声的位置。设计了相关实验,对干涉条纹图像中识别出的散斑噪声区域进行修补,消除了包裹相位图中一个条纹周期内相邻像素点间大于π的相位突变。     

A simple method to simulate diffraction and speckle patterns with a PC

A simple, intuitive and pedagogical method is proposed in order to simulate the phenomenon of light diffraction in simple cases. A diffracting plane obstacle is simulated by means of a model with a variable transmittance from one point to another. A numerical matrix is built with transmittance values at those points taken as samples. The matrix is handled with the Matlab program, and the Fraunhofer approximation is used. The method is applied to variable module and constant phase transmittance obstacles in single slit, double slit, square window and round window cases. The method is also applied to an obstacle with a constant reflectance module and random variable phase with Gaussian statistics, which gives rise to speckle phenomenon.     

Experimental evidence of the phase reversal in diffraction patterns

In a diffracted wavefield occurs in patterns phase variations. The most familiar example is the Fraunhofer diffraction pattern through a single slit: the theory predicts that the side bands of the diffraction pattern alternate in phase. This paper deals with phase reversal phenomenon in diffraction patterns. Two interesting systems are recognized: the diffraction through a half plane and the diffraction through a single slit.     

Stochastic optimization of quantized diffraction optical elements to form longitudinal intensity distributions

A stochastic approach to optimization of quantized diffraction optical elements (DOEs) intended to form specified longitudinal intensity distributions is considered.