Optic flaws detection and location based on a plenoptic camera

In this Letter,we propose an on-line inspection method based on a plenoptic camera to detect and locate flaws of optics.Specifically,due to the extended depth of field of the plenoptic camera,a series of optics can be inspected efficiently and simultaneously.Moreover,the depth estimation capability of the plenoptic camera allows for locating flaws while detecting them.Besides,the detection and location can be implemented with a single snapshot of the plenoptic camera.Consequently,this method provides us with the opportunity to reduce the cost of time and labor of inspection and remove the flaw optics,which may lead to performance degradation of optical systems.     

波前编码景深延拓与几何光学景深的关系

波前编码成像系统将模拟编码方法与数字解码技术相结合解决景深延拓问题,可以用信息光学的方法进行分析,得到波前编码系统的景深延拓扩展率。但是这种方法使用的景深概念和几何光学的景深概念有所不同。从几何光学角度研究了信息光学导出的波前编码系统的景深延拓扩展率与几何光学景深延拓的关系。最后得出结论,在F数一定的情况下,随着探测器分辨率的提高,几何光学景深延拓扩展率与信息光学给出的波前编码光学系统的景深延拓扩展率趋于一致。     

基于线性相位反演技术的自适应光学闭环实验研究

利用成像光学系统、变形镜、装有图像采集卡和D/A卡的PC机等建立了一套基于线性相位反演技术的自适应光学闭环实验系统.在Windows操作系统下用VC完成图像处理和控制算法.利用一台高测量精度的哈特曼传感器测量波前信息并评价自适应光学系统的校正效果.在不同像差大小状态下研究了这种基于线性相位反演技术的自适应光学系统的像差校正能力.收敛速度,稳定性等.实验结果表明,基于线性相位反演技术的自适应光学系统对静态小像差有较好的校正效果.     

用于活体人眼视网膜观察的自适应光学成像系统

利用自适应光学技术,研制了两套活体人眼视网膜高分辨力成像系统,在实时校正人眼波前误差的基础上,实现活体人眼视网膜细胞尺度的高分辨力成像。这两套系统分别采用19和37单元小型压电变形反射镜作为波前校正元件,哈特曼-夏克(Hartmann-Shack)波前传感器测量波前误差,用眼底反射的半导体激光作为波前探测的信标。在用计算机控制自适应光学系统实现人眼波前误差校正后,触发闪光灯照明视网膜,用CCD相机记录视网膜的高分辨力图像。校正后的残余波前误差的均方根值已分别小于1／6和1／10波长,相当于视网膜上成像分辨力分别为3．4μm和2．6μm,接近衍射极限。试验表明37单元系统的成像质量更好。     

开环双脉冲液晶自适应光学视网膜成像系统

为了获得高分辨率视网膜图像,利用液晶空间光调制器作为波前校正器建立了一套开环液晶自适应光学视网膜成像系统。与闭环模式相比,采用开环模式后,系统的能量利用率提高了1倍。系统采用双脉冲照明方式,以减少人眼曝光量,保护人眼安全。在照明光学系统中加入了大小视场切换装置使成像视场由之前的0.8°增至1.7°。同时优化了系统的时序控制流程,对人眼像差连续校正的同时快速调节成像相机的前后位置至最佳像面。对于开环模式对动态人眼像差的校正精度进行了测量,实验测得,经开环校正后,残差波面的均方根值约为0.09λ;相应的斯特雷尔(Strehl)比高于0.70,系统分辨率接近光学衍射极限的分辨率。对两名志愿者进行了实验,获得了清晰的眼底视网膜细胞图像。     

奇对称型相位板波前编码成像系统的点列图分析

基于几何光学理论利用光线追迹方法得到了适用于任意面型相位板的大视场平行光入射情况下的光线像差近似表达式,并在此基础之上分析了奇对称型相位板波前编码系统的点列图的大小、边界以及光线结构等特性,研究了大视场角平行光入射下的光线像差增强及点列图形变等现象,并且给出了相应的近似数学解析式来描述这些特性。通过对奇对称型相位板波前编码成像系统的点列图特性分析,有助于进一步的理解波前编码技术并且指导实际系统的设计。     

The fractional Fourier transform as a simulation tool for lens‐based X‐ray microscopy

The fractional Fourier transform (FrFT) is introduced as a tool for numerical simulations of X‐ray wavefront propagation. By removing the strict sampling requirements encountered in typical Fourier optics, simulations using the FrFT can be carried out with much decreased detail, allowing, for example, on‐line simulation during experiments. Moreover, the additive index property of the FrFT allows the propagation through multiple optical components to be simulated in a single step, which is particularly useful for compound refractive lenses (CRLs). It is shown that it is possible to model the attenuation from the entire CRL using one or two effective apertures without loss of accuracy, greatly accelerating simulations involving CRLs. To demonstrate the applicability and accuracy of the FrFT, the imaging resolution of a CRL‐based imaging system is estimated, and the FrFT approach is shown to be significantly more precise than comparable approaches using geometrical optics. Secondly, it is shown that extensive FrFT simulations of complex systems involving coherence and/or non‐monochromatic sources can be carried out in minutes. Specifically, the chromatic aberrations as a function of source bandwidth are estimated, and it is found that the geometric optics greatly overestimates the aberration for energy bandwidths of around 1%.     

A modified phase diversity diffraction wavefront sensor with a grating

The phase diversity wavefront sensor is one of the tools used to estimate wavefront aberration, and it is often used as a wavefront sensor in adaptive optics systems. However, the performance of the traditional phase diversity wavefront sensor is limited by the accuracy and dynamic ranges of the intensity distribution at the focus and defocus positions of the CCD camera. In this paper, a modified phase diversity wavefront sensor based on a diffraction grating is proposed to improve the ability to measure the wavefront aberration with larger amplitude and higher spatial frequency. The basic principle and the optics construction of the proposed method are also described in detail. The noise propagation property of the proposed method is also analysed by using the numerical simulation method, and comparison between the diffraction grating phase diversity wavefront sensor and the traditional phase diversity wavefront sensor is also made. The simulation results show that the diffraction grating phase diversity wavefront sensor can obviously improve the ability to measure the wavefront aberration, especially the wavefront aberration with larger amplitude and higher spatial frequency.     

A modified phase diversity wavefront sensor with a diffraction grating

Phase diversity wavefront sensor is one of the useful tools to estimate the wavefront aberration, and it is often used as a wavefront sensor in adaptive optics system. However, the performance of the traditional phase diversity wavefront sensor is limited by the accuracy and dynamic ranges of the intensity distribution at focus and defocus positions of the CCD camera. In this paper, a modified phase diversity wavefront sensor based on a diffraction grating is proposed to improve the ability to measure the wavefront aberration with larger amplitude and higher spatial frequency. The basic principle and the optics construction of the proposed method are also described in detail. The noise propagation property of the proposed method is also analysed by using the numerical simulation method, and comparison between the diffraction grating phase diversity wavefront sensor and the traditional phase diversity wavefront sensor is also made. The simulation results show that the diffraction grating phase diversity wavefront sensor can obviously improve the ability to measure the wavefront aberration, especially the wavefront aberration with larger amplitude and higher spatial frequency.     

Experimental validation of closed-loop adaptive optics based on a self-referencing interferometer wavefront sensor and a liquid-crystal spatial light modulator

A closed-loop adaptive optics system based on a self-referencing interferometer wavefront sensor (SRI WFS) using phase-shifting point-diffraction technique and an electrically addressed phase-only liquid-crystal spatial light modulator (LC SLM) is built and validated experimentally. The wavefront aberration of incoming beam is directly measured by analyzing four frames phase-shifted interferograms captured by a single CCD camera in two camera shots, and then by loading the conjugate function onto the SLM the wavefront aberration is corrected. The proposed scheme does not rely on any complicated control algorithm or wavefront-reconstruction algorithm and can achieve high-resolution and high-accuracy correction. Closed-loop correction results of single order Zernike aberrations and a Kolmogorov turbulence phase screen show that considerable improvements in the Strehl ratio (of greater than 0.94) is achieved.     

大气湍流畸变对空间目标清晰干涉成像仿真研究

本文利用功率谱反演法分别展开对符合 Kolmogonov 统计规律和修正后的Von Karmen 统计规律的大气湍流畸变波前相位屏进行了数值模拟研究. 得到各种模型下相位屏对该成像系统干涉成像图. 仿真结果表明, 采用闭合相位原理, 基本可以消除大气湍流对光束波前的影响, 验证了采用相位闭合技术的优势.     

The analysis of ray aberration of arbitrary phase mask in the wavefront coding system

The analyses of the imaging performance of the wavefront coding system are always based on the Fourier optics. In this paper, geometrical optics is used to analyze the imaging characteristics of arbitrary phase mask in the wavefront coding system. The characteristics of the spot diagrams created by odd and even symmetrical phase masks, including the size, upper and lower boundaries, ray structure, and the stability, are analyzed by the ray aberration theory. These characteristics are also compared with those obtained by Fourier optics, and the two sets of characteristics are proved to be consistent with each other quite well.     

对Talbot自成像和几何成像关系的分析

针对Talbot自成像与几何光学成像毫无关系的传统观点,本文提出了一种用于几何光学成像原理和物理光学成像原理对光栅成像进行对比分析的方法,发现在某一特殊的Talbot成像距离处,光栅自成像和几何成像有相同的成像规律,当光源为单色光照射时可以认为光栅的几何成像实际上是某一个特殊位置的Talbot像.     

光子计数成像技术及其应用

介绍光子计数实时图像采集实验系统，其中的高亮度增益的光子成像头通过超强光力中继透与高帧频电荷耦合器摄像机耦合；分析和介绍了单光子成像模式下系统工作的受限条件和多光子工作模式下系统的主要综合性能指标－读出噪声的测定方法。文中给出在自适应光学弱光波前传感中的应用，光子噪声分布规律以及光的波粒二象性实验验证等例子。     

一种基于全息术的光学系统闭环像差补偿方法

提出了一种基于21单元变形镜与全息波前传感器的全息自适应光学系统, 并对其像差校正能力进行了分析. 首先描述了全息波前传感器基本原理, 并在薄全息图近似下给出基于快速傅里叶变换算法的全息波前传感器数值模型; 然后基于21单元变形镜的数值模型, 分析了该变形镜的波前校正能力; 在此基础上, 数值模拟并实验验证了全息自适应光学系统对静态像差的闭环校正能力.     

In vivo fluorescent imaging of the mouse retina using adaptive optics

In vivo imaging of the mouse retina using visible and near infrared wavelengths does not achieve diffraction-limited resolution due to wavefront aberrations induced by the eye. Considering the pupil size and axial dimension of the eye, it is expected that unaberrated imaging of the retina would have a transverse resolution of 2 microm. Higher-order aberrations in retinal imaging of human can be compensated for by using adaptive optics. We demonstrate an adaptive optics system for in vivo imaging of fluorescent structures in the retina of a mouse, using a microelectromechanical system membrane mirror and a Shack-Hartmann wavefront sensor that detects fluorescent wavefront.     

基于GPU的液晶自适应光学波前重构计算

利用GPU进行液晶自适应光学波前重构的加速计算.介绍了液晶自适应光学的Zernike模式波前重构算法,详细论述了GPU的通用架构和GPU实现波前重构的方法,给出了GPU与CPU的实验对比结果.结果表明,GPU计算波前重构不但可以准确无误地计算出液晶波前校正器的灰度级分布,计算速度更是传统CPU波前计算的几十倍.     

基于位相变更的非相干数字全息自适应成像

菲涅耳非相干数字全息作为一种非扫描的三维成像技术具有其独特的优势,但其成像过程中会受到各种像差的影响,导致成像分辨率、再现像的质量降低.为了解决这一问题,可以结合适当的自适应光学技术对波前像差进行探测和校正.位相变更是一种基于两幅具有已知位相差的强度图像实现波前探测和像差校正的技术.本文发展了基于位相变更的非相干数字全息自适应成像技术,不需要引入引导星,利用全息记录过程中的两幅相移全息图,实现波前像差的探测.本文给出了所发展技术的数值仿真和实验结果,结合位相变更算法求解出系统像差的位相分布,将像差的共轭位相加载到光瞳面上,在全息图记录的同时校正像差,从而提高重建像的质量.     

微机械薄膜变形镜自适应光学系统实验研究

为求出自适应光学系统的最优校正电压, 提出了一种基于改进奇异值分解的闭环迭代控制算法。该算法可通过调节控制参量g1,g2和w,优化模式的收敛速度, 使控制信号快速收敛到一个可靠的局部最优解。搭建基于微机械薄膜变形镜(MMDM)的自适应光学系统, 测量光学影响函数并验证单个电极电压和镜面变形之间的准平方线性关系, 以及各个驱动器电极响应之间的线性叠加性。分别采用模拟眼和人眼出射波前作为原始波前进行实验。实验结果表明, 改进算法能快速有效地对静态或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。     

高功率激光装置中局部波前畸变的非线性传输

 根据高功率激光装置中强激光束传输的特点，建立了描述光束通过光学元件时引入的局部波前畸变模型，并利用纹波传输的线性化处理方法，研究了带有局部波前畸变的高强度光束的传输规律。以一个连续的非增益激光介质为例，用该模型进行数值模拟，给出了不同空间尺度的局部波前畸变的频谱分布、不同空间频率的纹波引起的振幅非线性增长曲线、不同B积分的非线性增益随光束传输距离的变化曲线,光束振幅非线性增益达到最大时光束的传输距离和标准传输距离不同时由局部波前畸变引入的振幅分布。研究表明为了防止光学元件损坏，应避免光学元件表面出现半径为0.5~2.0 mm的局部瑕疵。