信息光学 光学滤波与频谱分析

O438.2∥TB92 2006032128窗口傅里叶变换的三维面形测量= Windowed Fouriertransformfor 3-Dshape measurement[刊,中]/付艳华(四川大学电子信息学院光电系.四川,成都(610064)) ,陈文静…∥激光杂志.—2006 ,27(1) .—39 ,41提出在基于频谱分析的三维面形测量中,用窗口傅里叶变换( WFT)代替传统的快速傅里叶变换(FFT)去获取三维物体面形分布。理论分析和实验结果表明,窗口傅里叶变换不但可以减小频谱混叠对测量精度的影响,并且若在窗口傅里叶变换的处理过程中,设置合理的“门限”,还能够有效地抑制噪声,从而在一定程度上保证了基于频谱…     

激光大气闪烁的高频谱特性

 采用三波长闪烁仪进行了大气边界层的光传输实验，结果表明：在相同的传播条件下，非平面波激光大气闪烁功率谱的高频部分与波长存在着一定的关系，功率谱无标度区间的斜率即标度指数是一个与湍流强度、波长等因素有关的函数，在满足弱起伏的条件下，标度指数一般与波长呈负相关，波长愈长则标度指数愈小，频谱下降的趋势愈快；波长愈短则标度指数愈大，频谱下降的趋势愈慢。     

无透镜傅里叶变换全息图在欠采样条件下的数值再现分析

在理论分析无透镜傅里叶变换全息图记录的基础上，结合CCD的结构特点，用傅里叶频谱方法具体研究了无透镜傅里叶变换全息图在欠采样条件下的再现问题.指出在无透镜傅里叶变换全息术中，对有限尺寸物体而言，在记录过程不满足申农（Shannon）采样定理的条件下，仍能完整再现出物体的像.同时对再现像的变化特点进行了理论说明.所得的实验结果与理论分析一致.     

频域干涉测量中脉冲延迟时间测定方法的研究

在基于超短激光脉冲频域干涉技术的超快激光与物质相互作用的测量实验中,束一束间的延迟时间对瞬态特性的测量至关重要。利用两束脉冲频谱干涉条纹宽度与脉冲相对延迟时间成反比关系这一特性,阐述了通过对脉冲频谱干涉图进行傅里叶变换,在干涉条纹傅里叶变换面（时间域）上测量脉冲延迟时间的基本原理,并给出了测量误差分析,数值模拟结果显示通过傅里叶变换的方式,在频谱干涉图的时间域上可以有效地提取出两束脉冲间的相对延迟时间。     

改进4f傅里叶光学系统实现平面分形的频谱放大和小波变换

设计了一种改进的４ｆ傅里叶光学信息处理系统,利用该系统实现对频谱面坐标尺度的放在和光学小波变换。其优点是有利于带通滤波器的制作和精确定位。并给出了谢尔宾斯基（Ｓｉｅｒｐｉｎｓｋｉ）分形的傅里叶变换、小波变换及分维测量的实验结果。     

结构光测量中快速相位解包裹算法的讨论

对Schofield等提出的快速傅里叶变换（采用4次傅里叶变换和4次逆傅里叶）解包裹算法和Volkov等提出的相位重建算法（仅采用两次傅里叶变换和一次逆傅里叶变换）进行了讨论,提出基于离散余弦变换的快速相位解包裹算法.指出前两种算法在处理一般带噪音的模拟相位图时具有明显的优势,其处理结果非常接近理想值,而在处理相位变化剧烈或不连续区域的实验相位图（采用四步相移法测量雕刻佛像的三维面形）时出现较大误差,甚至无法处理,而基于离散余弦变换算法能很好的解决这个问题,并且拥有比前两种算法更快的运算速度.在实际应用中,针对不同的相位图把Schofield所提出的算法与基于离散余弦变换的算法结合起来,可以解决大部分相位解包裹问题.     

小波变换轮廓术的测量范围研究

利用小波“脊”处的小波系数来提取变形条纹中的相位信息可以在很大程度上抑制条纹图中有用的基频分量与零频和其它谐波频率分量的混叠,弥补了傅里叶变换轮廓术的不足。从离散信号频域分析角度,推导了变形条纹小波变换的频谱描述形式,讨论了其测量范围,包括结构条件和抽样条件。结果表明,只有在无周期内瞬时频谱混叠,即任意位置处物体瞬时高度变化满足h/xx=b<1/3条件时,和不存在抽样引起的周期间瞬时频谱混叠的抽样条件下(即一个周期内的抽样点数m≥4时),小波变换轮廓术才能正确恢复被测物体的三维面型。计算机模拟和实验验证了该结论。     

啁啾脉冲频域干涉仪相位重建方法的理论研究

理论研究了啁啾脉冲频域干涉仪的时域相移重建技术,对于接近实际的频谱干涉条纹,分别采用傅里叶变换和小波变换的方法完成了时域相位扰动信号的重建。傅里叶变换方法产生的重建误差受到滤波参数的影响,相对而言,小波变换方式解谱过程中,不需要进行特意的滤波操作,从而避免了重建结果存在误差不确定性的问题。     

脉冲相干激光雷达测距信号研究

对脉冲激光雷达外差测距信号进行了研究，理论上，采用调Q激光脉冲的数值计算波形，研究了脉冲激光经远处目标漫反向后进行外差接收的波形及其傅里叶变换频谱成分。实验上，研究了可调谐电光调Q射频激励波导CO2激光器脉冲激光经目标反射后的外差波形及其傅里叶变换频谱成分，并计算了目标的距离，理论分析与实验结果一致。     

激光大气传输湍流扰动仿真技术

为了研究激光大气传输时湍流效应对激光应用技术的影响,对湍流扰动的仿真进行了分析。介绍了在实验室内进行激光大气传输湍流扰动研究的数值仿真技术和仿真系统。阐述了快速傅里叶变换（FFT）和Zernike多项式两种湍流扰动数值仿真方法,并且对比了两种方法的优劣。利用物理相位屏搭建了实物湍流仿真系统,介绍了其理论模型并进行了仿真实验,对激光经湍流系统传输后的光强能量分布进行了研究分析。结果显示,室内湍流仿真系统能够准确地模拟弱起伏条件下湍流对激光传输的影响。     

大气边界层各向异性的室内模拟研究

 边界层的各向异性研究对于了解实际大气的湍流特性和经典理论的适用范围均具有较大的意义。利用室内水槽实验模拟了实际大气边界层，使用小波变换方法分析了对数光强起伏谱的特征，将获得的标度指数与理论值进行比较，结果表明混合层在水平方向较为接近各向同性，而垂直方向则呈现一定的各向异性。     

Dynamical and spatial aspects of sandpile cellular automata

The Bak, Tang, and Wiesenfeld cellular automaton is simulated in 1, 2, 3, 4, and 5 dimensions. We define a (new) set of scaling exponents by introducing the concept of conditional expectation values. Scaling relations are derived and checked numerically and the critical dimension is discussed. We address the problem of the mass dimension of the avalanches and find that the avalanches are noncompact for dimensions larger than 2. The scaling of the power spectrum derives from the assumption that the instantaneous dissipation rate of the individual avalanches obeys a simple scaling relation. Primarily, the results of our work show that the flow of sand down the slope does not have a 1/f power spectrum in any dimension, although the model does show clear critical behavior with scaling exponents depending on the dimension. The power spectrum behaves as 1/f ² in all the dimensions considered.     

湍流折射率谱型对大气闪烁和相位起伏功率谱的影响

基于Taylor湍流冻结假设理论,在不同湍流折射率谱型条件下,推导得出了光波闪烁和相位起伏频谱的表达式;数值计算了湍流谱型中折射率标度指数、内尺度以及外尺度变化时对光波频谱的影响。结果表明:随着折射率起伏标度指数的增大,闪烁频谱的低频段不再仅为常数,高频段下降的幂率逐渐增大,同时相位频谱在整个起伏频率段下降的幂率越来越大;湍流内尺度的增加将引起光波频谱的高频段下降的幂率越来越大;而随外尺度的减小,闪烁频谱低频段的振幅减小,这种影响在大口径接收时较为明显,相位谱的低频段幂率减小。     

孔径接收下大气闪烁频谱的理论和实验研究

 基于孔径接收下的对数振幅时间相关函数，推导了弱湍流起伏条件下大气闪烁频谱的表达式，分析了接收孔径对大气闪烁频谱的影响。通过完成水平大气传输实验，实际测量了孔径接收下的大气闪烁频谱。实验结果验证了理论计算。结果表明，孔径接收下的大气频谱分为低频段和高频段两部分，低频谱为常数，高频谱呈幂指数关系变化，且幂指数为-11/3；随着接收孔径增大，频谱在各频率点上的幅值逐渐减小，其形状保持不变。     

半导体激光器低频噪声的Lyapunov指数计算和混沌状态判定

根据小波变换和混沌噪声理论,对半导体激光器低频噪声进行了实验和理论分析.应用相轨迹、功率谱、Lyapunov指数、关联维等方法,探讨了噪声混沌模型的可行性.实验证明半导体激光器低频噪声具有混沌特性.在理论上分析了产生混沌的原因,为研究其可靠性提供了理论基础. 关键词： 混沌 Lyapunov指数 小波变换 低频噪声     

Low Earth orbit satellite-to-ground optical scintillation: comparison of experimental observations and theoretical predictions

Scintillation measurements of a 1064 nm laser at a 5 kHz sampling rate were made by an optical ground station at the European Space Agency observatory in Tenerife, Spain while tracking a low Earth orbit satellite during the spring and summer of 2010. The scintillation index (SI), the variance of irradiance normalized to the square of the mean, and power spectra measurements were compared to theoretical predictions based on the Kolmogorov spectrum, the Maui3 nighttime turbulence profile, weak scintillation finite-beam wave theory, included receiver, and source aperture averaging with no free-fitting parameters. Good agreement was obtained, not only for the magnitude of the observed fluctuations, but also for the corresponding elevation angle dependence and shape of the power spectra. Little variation was seen for the SI between daytime and nighttime links. For all elevation angles, ascending and descending, the observed scintillation over extensive regions of the atmosphere is consistent with log-normal statistics. Additionally, it appears from the results presented here that the nighttime turbulence profile for the atmosphere above the observatory in Tenerife is similar to that above Haleakala in Maui, Hawaii.     

On Scaling in Relation to Singular Spectra

This paper relates uniform α-H?lder continuity, or $\alpha$-dimensionality, of spectral measures in an arbitrary interval to the Fourier transform of the measure. This is used to show that scaling exponents of exponential sums obtained from time series give local upper bounds on the degree of H?lder continuity of the power spectrum of the series. The results have applications to generalized random walk, numerical detection of singular continuous spectra and to the energy growth in driven oscillators. Received: 3 July 1996 / Accepted: 11 September 1996     

复杂传播路径条件下激光光强起伏特性研究

对复杂地形情况下实际湍流大气中的激光强度起伏进行了系统的实验观测,分析了光强起伏统计特征的周日及全年变化规律。结果发现：复杂地形情况下实际湍流大气中的激光光强起伏,不论是概率密度分布还是其功率谱等统计特征均与理论上的偏离很大。     

Power-Law Behavior in Geometric Characteristics of Full Binary Trees

Natural river networks exhibit regular scaling laws in their topological organization. Here, we investigate whether these scaling laws are unique characteristics of river networks or can be applicable to general binary tree networks. We generate numerous binary trees, ranging from purely ordered trees to completely random trees. For each generated binary tree, we analyze whether the tree exhibits any scaling property found in river networks, i.e., the power-laws in the size distribution, the length distribution, the distance-load relationship, and the power spectrum of width function. We found that partially random trees generated on the basis of two distinct types of deterministic trees, i.e., deterministic critical and supercritical trees, show contrasting characteristics. Partially random trees generated on the basis of deterministic critical trees exhibit all power-law characteristics investigated in this study with their fitted exponents close to the values observed in natural river networks over a wide range of random-degree. On the other hand, partially random trees generated on the basis of deterministic supercritical trees rarely follow scaling laws of river networks.     

Influence of non-kolmogorov turbulence on intensity fluctuations in laser satellite communication

Satellite laser communication holds the potential for high-bandwidth communication, but the atmosphere can significantly affect the capability of this type of communication systems for satellite-toground and ground-to-satellite data links to transfer information consistently and operate effectively. Usually the influence of atmosphere on satellite laser communication is investigated based on the Kolmogorov turbulence model. However, both increasing experimental evidence and theoretical investigations have shown that the Kolmogorov theory is sometimes incomplete to describe the atmospheric statistics properly, in particular, in some portions of the atmosphere. Considering a non-Kolmogorov turbulent power spectrum with power law −5 that describes the refractive-index fluctuations in the atmosphere above 6 km, we calculate the scintillation index of a lowest-order Gaussian-beam wave under the weak-fluctuation condition. Then, considering a combined power spectrum of refractiveindex fluctuations and using the expression obtained, we analyze the joint influence of the Kolmogorov turbulence from the ground to 6 km and non-Kolmogorov turbulence above 6 km on the scintillation indices of laser beams used in ground-to-satellite and satellite-to-ground laser communication links. We show that the scintillation index in satellite laser communication is equal to the sum of the scintillation indices induced by the Kolmogorov turbulence from ground to 6 km and that caused by the non-Kolmogorov turbulence above 6 km. Also we investigate variations of the scintillation index with the beam radius on the transmitter, wavelength, the radial distance, and zenith angle. Finally, comparing the scintillation index induced by these two turbulences with the conventional results, we show that the scintillation index induced by these two turbulences is a bit smaller than the conventional results.