基于光栅分光法的相干衍射成像

提出一种可以通过单次曝光实现 PIE(ptychographic imaging engine)成像的方法, 该方法用正交光栅将入射细光束衍射为传播方向不同的子光束簇以对样品进行照明, 并用CCD同时记录各个子光束所形成的衍射光斑阵列. 该方法很好地克服了现有PIE方法的成像质量易受机械扫描误差影响和数据采集时间过长两个缺点, 具有很好的实用价值. 关键词： 相干衍射成像 相位恢复 显微成像 迭代算法     

非相干照明条件下的ptychographic iterative engine成像技术

在传统多波长相干衍射成像理论的基础上提出适用于 X-射线和电子束等非相干光源照明成像的改进多波长ptychographic iterative engine 方法, 同时将小孔形状和照明光谱信息用于叠代计算, 可以在非相干照明条件下精确重建出物体的强度透射像和相位透射像, 并对光源带宽对重建精度的影响进行了分析, 对于解决如何在非相干照明条件下对大尺寸物体进行精确相位成像的问题具有较好的科研和实用价值.     

Full-field heterodyne interference microscope with spatially incoherent illumination

A heterodyne interference microscope arrangement for full-field imaging is described. The reference and object beams are formed with highly correlated, time-varying laser speckle patterns. The speckle illumination confers a confocal transfer function to the system, and by temporal averaging, the coherence noise that often degrades coherent full-field microscope images is suppressed. The microscope described is similar to a Linnik-type microscope and allows the use of high-numerical-aperture objective lenses, but the temporal coherence of the illumination permits the use of a low-power achromatic doublet in the reference arm. The use of a doublet simplifies alignment of the microscope and can reduce the cost. Preliminary results are presented that demonstrate full-field surface height precision of 1 nm rms.     

Phase retrieval using an aperture-array filter under partially coherent illumination

Recently we have proposed a deterministic phase retrieval method using an aperture-array filter to reconstruct a complex-valued object from a single diffraction intensity pattern. We describe here the effect of quasi-monochromatic partially coherent illumination on the object reconstruction by the phase retrieval method, and then present the method of eliminating the effect of the partially coherent illumination from the diffraction intensity pattern via a simple Fourier deconvolution operation provided that the complex degree of spatial coherence of the illuminating beam is known. The usefulness of this method is shown in computer-simulated examples of the object reconstructions under Gaussian Schell-model partially coherent illumination.     

激光空间相干性对照明均匀性的影响

 研究了激光相干性对照明均匀性的影响，为照明激光器的选择提供了理论参考。其中，部分相干高斯光束分解为模式间相互独立的厄米-高斯光束的迭加。采用相位屏的近似处理方法对激光通过大气湍流的传输进行计算模拟。数值模拟的结果表明：当照明光束的空间相干性降低时，其照明均匀度逐步提高。因此对于照明激光器而言，选择空间相干性较差的激光器对其照明均匀度更加有益。     

部分相干信息处理系统的噪声演绩(Ⅱ)——时间部分相干照明

本文研究了时间相干性对光学信息处理系统噪声演绩的影响。以输出信噪比作为信息处理系统噪声演绩的度量,系统中任意平面上的颗粒噪声及相位噪声作为主要的噪声源。结果表明,时间部分相干照明可以提高系统的输出信噪比,对系统的装置噪声有明显的抑制作用。     

Full-field and single-shot quantitative phase microscopy using dynamic speckle illumination

We developed an off-axis quantitative phase microscopy that works for a light source with an extremely short spatial coherence length in order to reduce the diffraction noise and enhance the spatial resolution. A dynamic speckle wave whose coherence length is 440 nm was used as an illumination source. To implement an off-axis interferometry for a source of low spatial coherence, a diffraction grating was inserted in the reference beam path. In doing so, an oblique illumination was generated without rotation of the wavefront, which leads to a full-field and single-shot phase recording with improved phase sensitivity of more than a factor of 10 in comparison with coherent illumination. The spatial resolution, both laterally and axially, and the depth selectivity are significantly enhanced due to the wide angular spectrum of the speckle wave. We applied our method to image the dynamics of small intracellular particles in live biological cells. With enhanced phase sensitivity and speed, the proposed method will serve as a useful tool to study the dynamics of biological specimens.     

基于多角度无透镜傅里叶变换数字全息的散斑噪声抑制成像研究

在数字全息成像中,散斑噪声严重影响了再现像的信噪比和成像分辨率,因此为了提高数字全息成像质量,迫切需要抑制再现像的散斑噪声.分析并给出了矩形散射光斑的强度协方差,定量计算了特定实验条件下产生退相关散斑图样的最小角度差.结合透镜的性质设计并搭建了多角度无透镜傅里叶变换数字全息成像系统,利用光纤端面在透镜焦平面的二维机械移动代替传统反射镜的旋转,使照明光束在不改变照明位置和大小的同时,可任意改变光束方向.移动光纤端面使多角度照明满足最小角度差,获取了81幅数字全息图.利用单次快速傅里叶逆变换实现数值再现,对多幅再现像的强度像求平均,实验结果表明散斑对比度降低为单幅再现像的14.6%,使图像信噪比提高了6.9倍.该抑制散斑的多角度数字全息成像方法有效的抑制了散斑噪声,且成像光路结构简单,可操作性强.     

Array illuminator based on self-imaging in white light

An array illuminator is a device/optical system that splits an incoming beam of light into an array of many light spots/beams. It is useful in logic systems and in optical digital computing or in switching systems to energize arrays of components such as logic gates, optically bistable devices and electro-optic modulators. Array illuminators working in white light are interesting because they do not suffer from coherent noise and yield better signal-to-noise ratio. We propose configurations for array illuminator based on Fresnel diffraction and working under white light illumination conditions. Performance evaluation of the illuminators is also undertaken and the results of investigation are reported.     

部分相干光栅衍射效应和干涉术

本文提出一种新的部分相干照明的光栅衍射干涉仪.先分析了光栅的介于Talbot和Lan效应之间的部分相干衍射效应.部分相干干涉图的特点是条纹由频率成倍的两种光栅状载波所表征.调整光源狭缝,系统在两相干性极端分别转成Talbot和Lau干涉仪.理论分析采用了模糊函数方法.最后给出了实验.     

Supercontinuum laser illumination applied to traditional optical flow imaging methods

The schlieren method of refractive flow visualization traditionally requires non-coherent illumination in order to avoid problems with coherent artifact noise and binary cutoff by the knife-edge. Related shadowgraph and Wollaston-prism schlieren-interferometer methods, however, work well with light sources of high spatial coherence. Here we apply a supercontinuum laser as a light source for these methods, providing spatially coherent white-light illumination. Excellent results are obtained with shadowgraphy and schlieren-interferometry, but the schlieren method still requires a modified cutoff in place of the traditional knife-edge for laser illumination. Once they become widely available, supercontinuum lasers will find frequent use in these optical instruments, especially the schlieren-interferometer.     

Spatial filtering dark hollow beams

We describe the synthesis of diffraction free beams and dark hollow beams with features easily tunable using a holographic transmittance. The hologram is generated by interfering two zero order Bessel beams with non-common axis. Spatial filtering techniques are implemented by controlling the illumination during the reconstruction process. The experimental results are for illumination similar to the one used in the recording process, obtaining a set of diffracting free beams. One of these beams propagates quasi-parallel to the surface hologram. For illumination with a plane wave we obtain a dark hollow beam propagating in the same direction as the reconstructions beam. Experimental results are shown in both cases.     

Resolution enhancement of random adsorbed single-molecule localization based on surface plasmon resonance illumination

Single-molecule localization (SML) is a powerful tool to overcome the diffraction limit in optical imaging, because the fluorescence emitted by single molecules can be observed with nanometer accuracy when the optical background and associated noise are made sufficiently small. Random adsorbed SML has been successfully demonstrated for superresolution imaging on metal surfaces. To optimize the random adsorbed SML, we developed a new illumination method based on surface plasmon resonance (SPR). The enhancement of the fluorescence signal and the reduction of background noise were achieved simultaneously. A high localization resolution of 15?nm was demonstrated with this new SPR illumination system.     

Lens-free coherent modulation imaging with collimated illumination

We propose a lens-free coherent modulation imaging(CMI) method for reconstructing a general complex-valued wave field from a single frame of a diffraction pattern. A numerical Fourier transform is introduced in the iterative reconstruction process to replace the lens or zone plate used in the current CMI technique to adopt the constraint on the Fourier components of the exit wave field of the sample. While the complexity of the experimental setup is remarkably reduced by replacing the zone plate and additional accessories with the numerical processing, the energy fluence loss induced by the undesired diffraction orders of the zone plate can be also avoided. The feasibility of the proposed technique is verified experimentally with visible light.     

超衍射极限相干反斯托克斯拉曼散射显微成像技术及其探测极限分析

理论上提出一种突破衍射极限限制的相干反斯托克斯拉曼散射显微成像方法, 并对其探测极限进行分析.通过引入环形附加探测光与艾里斑周边的声子作用, 实现点扩展函数的改造, 提高相干反斯托克斯拉曼散射显微成像系统的横向空间分辨率. 随着分辨率的提高, 信号强度也随之降低, 尤其当应用于生物学、医学研究时, 样品分子数密度通常很低, 这将导致信号探测更加困难. 因此分析系统的探测极限, 确定超分辨体积元内的最小可探测分子数是展开超衍射极限相干反斯 托克斯拉曼散射显微成像实验研究的重要前提. 当泵浦光、斯托克斯光、探测光光强均达到极大值, 分辨率约40 nm三维空间内, 超衍射极限相干反斯托克斯拉曼散射显微成像系统的散粒噪声信噪比由曝 光时间与样品分子数密度决定. 曝光时间若取20 ms, 探测极限约为10³, 样品分子数目只有大于探测极限, 才能保证信号可以从噪声背景中提取出来. 关键词： 突破衍射极限 相干反斯托克斯拉曼散射 非线性光学 探测极限     

Analysis of a partially coherent optical correlator in the presence of phase defects at the input plane

The effects of phase defects at the input plane of an optical correlator on the performance of the system under partially coherent illumination is investigated. The correlation signal-to-noise ratio (SNR) is evaluated as the criterion for the performance of the optical system. We study the effects of both spatially and temporally partially coherent illumination on the distorted correlation signal. It is shown that the output SNR can be increased by relaxing the coherence requirements of the system. The SNR dependence on noise variation is also investigated. It is found that the correlator becomes less sensitive to noise variations under partially coherent illumination.     

相干X射线衍射成像三维重建的数字模拟研究

利用相干X射线衍射成像“过采样”采集样品的远场相干衍射图样, 结合相位重建迭代算法重建物空间样品信息. 三维重建过程中, 边界约束条件是相位重建算法中最为关键的部分. 本文采用数字模拟的方法, 利用灰度值图像作为物空间的样品, 研究并实现了边界条件的自动寻找, 重建结果显示比以往采用较“松”的边界约束更为精确. 利用噪声模拟方法, 研究了衍射图样中不同噪声类型的滤除对重建结果的影响. 研究发现传统的去噪方法在高噪声情况下不能直接应用于相干X射线衍射成像, 并找到了适用于相干X射线衍射成像噪声滤除的有效方法. 研究表明, 此方法能非常有效地降低噪声对重建结果的影响. 利用模拟三维纳米金颗粒作为样品, 完成了对纳米金颗粒中电子密度分布的三维重建, 在有随机噪声的影响下, 也得到了很好的重建结果, 并找到了成功实现三维重建的噪声限为信噪比不低于27. 关键词： X射线相干衍射成像 过采样 三维相位重建 显微成像     

Coherent information processing by a pair of lenses in spherical wave illumination

A coherent optical information system has been analysed using the Fresnel diffraction theory. Considering the spherical wave illumination, the same system is used for spatial filtering and subsequent reimaging. The conditions for locating the spatial frequency plane and the image plane have been pointed out. The scale of the Fourier transform can be controlled by three degrees of freedom. The final image formed is inverted and magnified with respect to the input signal. The present analysis has been compared with those of Pernick and Moharir. Aberrations involved have also been discussed.     

平场复用多焦点结构光照明超分辨显微成像

多焦点结构光照明显微技术(multifocal structured illumination microscopy, MSIM)能在50μm的成像深度内和1Hz的成像速度下实现两倍于衍射极限分辨率的提升,相比传统的宽场结构光照明显微技术,具有较大的成像深度和层析能力,更适合应用于厚样品的长时程三维超分辨成像.然而, MSIM存在成像速度慢、图像处理过程复杂等问题.本文提出了一种基于平场复用多焦点结构光照明的快速超分辨显微成像方法和系统(flat-field multiplexed MSIM, FM-MSIM),通过在照明光路中插入光束整形器件,将高斯光束转变为均为分布的平顶光束,提高激发点阵的强度均匀性和扩大视场;通过将每个衍射受限的激发点沿y方向延长,形成新的多路复用多焦点阵照明图案,提高能量利用率,减少扫描步数,进而提高成像速度和信噪比;结合基于多重测量矢量模型的稀疏贝叶斯学习图像重构算法,简化图像重构步骤,在保证空间分辨率的同时实现至少4倍于传统MSIM的成像速度.在此基础上,利用搭建的FM-MSIM系统进行了BSC细胞微管样片和小鼠肾切片标准样片的超分辨成像实验,实验结果证明...     

Using diffractograms to evaluate optical systems with coherent illumination

A new approach to measuring aberrations of an optical system with coherent illumination is introduced. The optical system is evaluated by use of a so-called weak phase object and by digital image recording and processing. Based on the contrast transfer function theory for coherent systems, the main aberrations of the optical system can be determined. This is a convenient approach to evaluating and measuring complex optical systems with numerous optical elements after assembly and can serve as a simple performance test of an optical instrument in the field.