利用Zernike多项式对湍流波前进行波前重构

分析了利用Ｚｅｒｎｉｋｅ多项式进行波前重构时模式耦合与混淆产生的原因，以及模式耦合与混淆对受大气湍流影响的光学波前进行波前重构的精度和稳定性的影响。取除去平移的前６５项Ｚｅｒｎｉｋｅ多项式构造湍流波前。针对６１单元自适应光学系统的波前传感器子孔径布局进行仿真，通过比较Ｎｓ不同取值时的湍流波前重构精度和稳定性，得出了该条件下Ｎｓ的最佳取值。     

自适应光学系统中变形镜和波前传感器共轭位置要求的分析

通过对几何光学和物理光学模型的数值计算,分析了自适应光学系统中小像差畸变波前在空间自由传播时自身的变化情况,进而给出了系统中对变形镜和波前探测器与被校正瞳面之间共轭位置关系的要求和允许范围.结果表明,波前自由传播时的变化程度决定于像差自身的类型和大小、光束的口径以及传播的距离,大口径小像差波前近距离传播时波前变化误差很小.一般来说,变形镜和波前传感器偏离被校正瞳面共轭位置距离满足菲涅尔数大于1000时,对系统校正效果的影响可以忽略.实际应用中,应该根据校正对象的特征来具体计算波前误差随传播距离的变化,从而设计波前传感器和变形镜的位置,以及选择使用4F光学系统.本文的分析可以为自适应光学系统的整体光路设计提供一定理论参考.     

自适应光学技术文献文摘与索引

本文评论了包括多元高频振动COAT、锐度函数最大化和相位共轭在内的基本自适应光学技术。叙述了自适应波前补偿系统的设计,并重点叙述了波前探测器和波前校正器。特别考虑了一种径向Ronchi光栅横向剪切千涉仪波前探测器。研究了目前正使用的自适应光学系统。     

基于MEMS技术的自适应光学系统的研究

用自适应光学系统来校正由大气湍流等产生的波前畸变,能够得到很好的效果.通过对自适应光学系统的工作原理进行研究,提出了一种基于MEMS技术的微小型自适应光学系统校正波前畸变的方法,将MEMS技术应用于变形反射镜,并构建了具体的实验平台,用来校正一种人为产生的波前畸变,且阐述了具体的实验过程.实验结果表明,基于MEMS技术的自适应光学系统能够很好地闭环校正波前畸变,且其体积小、质量轻、校正性能稳定,为自适应光学技术在星载相机上的应用提供了依据.     

相位共轭自适应光学回波算法和多目标捕获特性

本文首次用回波算法导出相位共轭自适应光学系统的三个前提条件,论证了在大气扰动中实现波前校正的可行性,并对相位共轭自适应光学系统的多目标捕获特性进行了讨论。     

基于部分岭估计的Zernike模式法人眼波前像差重建

为了提高自适应光学系统中人眼波前像差的重建精度,进而提高自适应光学图像中的点扩散函数重建精度,提出了一种基于部分岭估计的Zernike模式前重建算法。首先,基于Zernike模式波前重建模型,分析了常用的模式系数求解方法;其次,在最小均方误差意义下,将部分岭估计的概念引入到自适应光学系统的波前重建算法中,通过确定最优岭估计参数来改善最小二乘估计的奇异性,从而抑制波前探测中测量误差的进一步被放大;最后,讨论了在波前斜率误差的影响下由两种算法所产生的误差大小。仿真实验结果表明：在波前重建算法中引入部分岭估计可有效减小模式系数的均方误差,相对于奇异值分解法减小了8%~10%,在波前探测测量误差增大的情况下,部分岭估计的波前重建精度要高于最小二乘估计法,有利于自适应光学后期中基于波前探测的图像复原研究。     

微机械薄膜变形镜的闭环校正模型

介绍了微机械薄膜变形镜(MMDM)面形影响函数的意义,并测量了Oko公司37通道MMDM的面形影响函数矩阵,实验验证了镜面形变和单个驱动电极电压平方之间的线性关系,分析了变形镜的校正能力,建立了自适应光学系统闭环校正的模型.搭建基于MMDM的自适应光学实验系统,采用人眼出射波前作为原始波前进行实验,结果表明,模型能快速有效的对动态畸变波前进行校正,为基于MMDM的自适应光学系统提供了算法支持.     

H—S法波前探测的高速图象采集系统

自适应光学系统中有两种方法用于测定波前的局部斜率：剪切干涉测量法和哈特曼法（以下简称Ｈ－Ｓ法）。由于Ｈ－Ｓ法运用较简单的光学系统，无需任何活动组件，具有较高的光效率，并能很好地用于探测器阵列，因此它更普遍地用于自适应光学系统中。本文介绍了一种应用于Ｈ－Ｓ法波前探测的高速图象采集系统，提出了应用本图象采集系统解决高帧频探测器阵列与数据处理机之间的同步协调的方法。     

H－S法波前探测的高速图象采集系统

自适应光学系统中有两种方法用于测定波前的局部斜率：剪切干涉测量法和哈特曼法（以下简称Ｈ－Ｓ法）。由于Ｈ－Ｓ法运用较简单的光学系统，无需任何活动组件，具有较高的光效率，并能很好地用于探测器阵列，因此它更普遍地用于自适应光学系统中。本文介绍了一种应用于Ｈ－Ｓ法波前探测的高速图象采集系统，提出了应用本图象采集系统解决高帧频探测器阵列与数据处理机之间的同步协调的方法。     

用Hartmann—Shack传感器测量激光束的波前相位

Ｈａｒｔｍａｎｎ－Ｓｈａｃｋ传感器已经用于自适应光学系统。它可以同时探测出一束光的振幅和相位信息。通过一个位置传感器，比如ＣＣＤ，它就可以成为一种对光学系统和光束的静态和动态质量诊断的有力工具。从Ｈ－Ｓ波前传感器的输出（波前斜率和近场强度分布），就可以推算出远场特点，如ＰＳＦ和ＯＦＴ。本文将介绍波前重构的理论分析和远场特征评估。同时也给出了光束质量的静态和动态的测量结果。     

Correctability limitations imposed by plane-wave scintillation in multiconjugate adaptive optics

Plane-wave scintillation is shown to impose multiconjugate adaptive optics (MCAO) correctability limitations that are independent of wavefront sensing and reconstruction. Residual phase and log-amplitude variances induced by scintillation in weak turbulence are derived using linear (diffraction-based) diffractive MCAO spatial filters or (diffraction-ignorant) geometric MCAO proportional gains as open-loop control parameters. In the case of Kolmogorov turbulence, expressions involving the Rytov variance and/or weighted C(2)(n) integrals apply. Differences in performance between diffractive MCAO and geometric MCAO resemble chromatic errors. Optimal corrections based on least squares imply irreducible performance limits that are validated by wave-optic simulations.     

Layer-oriented adaptive optics for solar telescopes

First multiconjugate adaptive-optical (MCAO) systems are currently being installed on solar telescopes. The aim of these systems is to increase the corrected field of view with respect to conventional adaptive optics. However, this first generation is based on a star-oriented approach, and it is then difficult to increase the size of the field of view beyond 60-80?arc sec in diameter. We propose to implement the layer-oriented approach in solar MCAO systems by use of wide-field Shack-Hartmann wavefront sensors conjugated to the strongest turbulent layers. The wavefront distortions are averaged over a wide field: the signal from distant turbulence is attenuated and the tomographic reconstruction is thus done optically. The system consists of independent correction loops, which only need to account for local turbulence: the subapertures can be enlarged and the correction frequency reduced. Most importantly, a star-oriented MCAO system becomes more complex with increasing field size, while the layer-oriented approach benefits from larger fields and will therefore be an attractive solution for the future generation of solar MCAO systems.     

Modeling and correction of incoherent wavefront distortion

There are two types of wavefront distortion inside the female breast: incoherent scattering and coherent interference. Adaptive wavefront compensation algorithms developed so far are useful for correction of incoherent distortion caused by scattering. The performances of these algorithms differ according to the extent of wavefront amplitude distortion. It is shown analytically and experimentally in this article that the matched filtering approach, while optimal for detection, is not so for imaging when the wavefront amplitude is distorted in addition to phasefront distortion. Matched filtering algorithms increase wavefront amplitude variance and therefore decrease image contrast. The inverse filtering approach, while ideal for fidelity, is not stable when the signal-to-noise ratio is low. An approach toward inverse filtering, amplitude compression operation in addition to phase deaberration, is introduced in this article. Analysis and experiments show that its performance is superior to matched filtering algorithms and to time-delay type correction algorithms without introducing stability problems. © 1996 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 8, 322–335, 1997     

Multiconjugate adaptive optics results from the laboratory for adaptive optics MCAO/MOAO testbed

We report on the development of wavefront reconstruction and control algorithms for multiconjugate adaptive optics (MCAO) and the results of testing them in the laboratory under conditions that simulate an 8 meter class telescope. The University of California Observatories (UCO) Lick Observatory Laboratory for Adaptive Optics multiconjugate testbed allows us to test wide-field-of-view adaptive optics systems as they might be instantiated in the near future on giant telescopes. In particular, we have been investigating the performance of MCAO using five laser beacons for wavefront sensing and a minimum-variance algorithm for control of two conjugate deformable mirrors. We have demonstrated improved Strehl ratio and enlarged field-of-view performance when compared to conventional AO techniques. We have demonstrated improved MCAO performance with the implementation of a routine that minimizes the generalized isoplanatism when turbulent layers do not correspond to deformable mirror conjugate altitudes. Finally, we have demonstrated suitability of the system for closed loop operation when configured to feed back conditional mean estimates of wavefront residuals rather than the directly measured residuals. This technique has recently been referred to as the "pseudo-open-loop" control law in the literature.     

Analysis and correction of ultrasonic wavefront distortion based on a multilayer phase-screen model

A model is introduced that incorporates the cumulative wavefront distortion effects caused by spatial heterogeneities along the path of propagation, and a corresponding model-based wavefront distortion-correction method is presented. In the proposed model, a distributed heterogeneous medium is lumped into a series of parallel phase screens. The distortion effects can be compensated-without a priori knowledge of the distorting structure-by backpropagation of received wavefronts through hypothetical multiple phase screens located between the imaging system and targets, while each pointwise time shift is adjusted iteratively to maximize a specified image quality factor at the final layer. Theoretical analyses indicate that the mean speckle brightness decreases monotonically with the root-mean-square value of distributed phase distortions; therefore, the speckle brightness can be used as an image quality factor. Experimental one-dimensional (1-D) array data with simulated distortion effects based on a real 2-D abdominal-tissue map were used to evaluate the performance of the proposed method and existing aberration-correction techniques. The simulated characteristics of wavefront distortion and relative performance of existing correction techniques were similar to reports based on abdominal-wall data and breast data. This investigation shows that the proposed method provides better compensation for wavefront distortion.     

Preconditioned conjugate gradient wave-front reconstructors for multiconjugate adaptive optics

Multiconjugate adaptive optics (MCAO) systems with 10(4)-10(5) degrees of freedom have been proposed for future giant telescopes. Using standard matrix methods to compute, optimize, and implement wavefront control algorithms for these systems is impractical, since the number of calculations required to compute and apply the reconstruction matrix scales respectively with the cube and the square of the number of adaptive optics degrees of freedom. We develop scalable open-loop iterative sparse matrix implementations of minimum variance wave-front reconstruction for telescope diameters up to 32 m with more than 10(4) actuators. The basic approach is the preconditioned conjugate gradient method with an efficient preconditioner, whose block structure is defined by the atmospheric turbulent layers very much like the layer-oriented MCAO algorithms of current interest. Two cost-effective preconditioners are investigated: a multigrid solver and a simpler block symmetric Gauss-Seidel (BSGS) sweep. Both options require off-line sparse Cholesky factorizations of the diagonal blocks of the matrix system. The cost to precompute these factors scales approximately as the three-halves power of the number of estimated phase grid points per atmospheric layer, and their average update rate is typically of the order of 10(-2) Hz, i.e., 4-5 orders of magnitude lower than the typical 10(3) Hz temporal sampling rate. All other computations scale almost linearly with the total number of estimated phase grid points. We present numerical simulation results to illustrate algorithm convergence. Convergence rates of both preconditioners are similar, regardless of measurement noise level, indicating that the layer-oriented BSGS sweep is as effective as the more elaborated multiresolution preconditioner.     

Wavefront error caused by centroid position random error

The wavefront error caused by centroid position random error is derived in detail, and an exact formula, which evaluates the wavefront error associated with the centroid position random error, is obtained when the Zernike modes are used as the basis for wavefront reconstruction. The formula is proved by two Shack–Hartmann wavefront sensors with different wavefront reconstruction matrices, and it can precisely describe the wavefront measuring error caused by centroid position random error.     

Real time diagnosis of transient pulse laser with high repetition by radial shearing interferometer

Transient, high repetition pulse laser can be applied to test numerous physical parameters, where in situ, real time measurement and isolation of vibration is highly demanded. Because of its short half-width, high power, high repetition, and even large distortion, the laser presents unique challenges to conventional diagnosing methods. A system based on a novel cyclic radial shearing interferometer is proposed to diagnose the transient, high repetition pulse laser with common path, no reference plane, and high precision. With the spatial-carrier methods, the system needs only one interferogram to reconstruct amplitude and wavefront of the laser. The theories of amplitude and wavefront reconstruction have been validated by computer simulation, and errors less than 1/1000lambda are obtained for both. Comparing with the results of the ZYGO interferometer, an error less than 1/20lambda for both peak-valley and root-mean-square values is gained with good repeatability for the wavefront. The calibration process and real time diagnosis of a high repetition pulse laser are presented then. Finally, the error consideration and system optimization are discussed in detail.     

基于B样条函数的快速波前复原

从斜率复原波前是夏克-哈特曼波前传感器这一类斜率采样探测器的核心流程.传统的复原算法中,区域法对局部波前的复原效果好,但易受斜率噪声的影响,同时空间分辨率较低;模式法抗噪能力强,但没有精确复原局部波前的能力.本文提出了基于B样条函数的快速复原算法,将波前展开为B样条曲面的线性组合,并将复原问题从斜率最小二乘问题转化为泊...