混浊介质显微成像中吸收作用的门机制

采用蒙特卡罗方法研究了混浊介质的吸收特性对共焦荧光显微成像的影响。结果表明,混浊介质对光的吸收作用增强了成像的分辨率,同时降低成像强度。因此,混浊介质样品对光的吸收作用是样品本身所固有的分辨散射光的门机制。     

混浊介质多光子激发显微成像的快速模型

将二维点扩散函数（PSF）和蒙特卡罗方法相结合,引入了一种研究混浊介质显微成像的快速仿真模型,将该模型用于混浊介质的多光子激发（MPE）显微成像研究,极大地提高了模拟效率,与直接蒙特卡罗方法计算结果的比较证实了该方法的正确性和有效性,此外,一个计算实例说明了混混介质的多光子激发显微成像具有比共焦荧光显微成像更优的横向分辨率。     

具有高成像精度的高速传感共焦显微成像方法

提出一种高速传感共焦显微成像方法(HSSCM)对样品表面形貌进行高效率、高精度的成像测量。HSSCM将共焦轴向响应曲线沿轴向平移S,然后将平移前后两条曲线相减并除以两曲线的和,继而构成具有不受样品反射率影响的、高信噪比的传感成像特性曲线。在实际扫描成像过程中,轴向扫描间隔同样设定为S对样品进行逐层逐点扫描,扫描完成后将每个测量点轴向多层扫描数据中光强最大值和光强次大值相减除以两者相加,然后利用传感成像特性曲线反算得到样品高度,通过获得每个测量点的样品高度便可实现对样品形貌的高精度测量和3D形貌重构。理论分析和实验表明,通过优选平移量S,和传统共焦显微成像方法相比,HSSCM在具有高成像精度的前提下将扫描成像效率提高了至少3倍。     

瞬发伽马活化成像的数学模型建立与模拟重建北大核心CSCD

瞬发伽马活化成像中,样品内部的中子自屏蔽和伽马自吸收效应会使测量结果产生不均匀分布。针对成像单元响应不一致的问题,研究了样品内部中子场不均匀分布和伽马自吸收效应的影响,并进行了理论推导,建立了用于修正成像单元响应和图像重建的数学模型,利用数学模型对Fe,H元素瞬发伽马活化成像的蒙特卡罗模拟进行了元素图像重建。结果显示,样品内中子场和γ自吸收对成像的影响得到明显改善,Fe和H元素的含量分布使用此模型可以被精确重建,验证了数学模型的有效性。     

基于代数重建算法的高能电子三维成像研究

本工作将代数重建算法应用于新兴发展的高能电子成像技术开展三维成像研究,实现对样品靶物质内部结构信息的精确诊断.通过蒙特卡罗程序及粒子追踪程序模拟高能电子成像过程,包括电子束与靶物质相互作用过程,获得样品靶物质成像角度下的高能电子二维成像结果.利用代数迭代重建ART(Algebraic Re-construction T...     

荧光共焦并行探测显微成像系统设计及实验

将数字微镜器件加入到荧光显微成像系统中,代替传统共焦显微系统中的照明针孔,利用其调制特性,通过在数字微镜器件上加载不同图片,实现对光束的分割.对马铃薯细胞分别进行四通道、六通道、九通道的荧光细胞探测,同时采用平面反射镜作为样品,测试得到系统的深度响应曲线,分析了系统的分辨率.实验结果表明,数字微镜器件的加入实现了从点对点共焦成像变为多点并行共焦显微成像,提高了显微成像的探测速度,同时具有较高的分辨率.     

同步辐射红外共聚焦谱学三维成像重建算法研究

为获取物质内部成分的三维分布信息,研究了基于同步辐射红外光源的共聚焦三维成像重建算法。采用单点探测器扫描成像的方式,根据同步辐射红外谱学显微共聚焦三维成像的原理及非线性特性,建立了同步辐射红外谱学显微共聚焦三维成像模型;根据该模型的特点建立测试样品的模型,模拟了红外谱学共聚焦三维成像测试,得到了共聚焦三维成像的测试数据;分别使用Levenberg-Marquardt算法和改进型高斯-牛顿算法对使用前向模型模拟采集得到的结果进行重建。结果表明,前向模型中未加入误差时,Levenberg-Marquardt算法可以重建样品的三维信息,在前向模型中加入1%误差时,Levenberg-Marquardt算法重建得到的结果与实际结果偏差较大,而改进型高斯-牛顿算法可以重建样品的三维信息。     

激光共焦LIBS显微成像系统的研制

针对复杂形貌样品微区化学成分难以表征的难题,研制了一套激光共焦诱导击穿光谱(LIBS)显微成像系统。该系统利用反射的连续激光构建高空间分辨的激光共焦显微系统,实现样品的精准定焦及三维形貌测量;利用共光路脉冲激光诱导激发等离子体光谱信号,实现样品微区全元素探测,进而实现具有高空间分辨、抗漂移特性的三维LIBS显微元素成像。实验表明,该系统可以实现横向分辨率为10μm的多元素图谱成像,系统光谱探测的合成不确定度为2.24%。该系统结合形貌信息和LIBS光谱信息实现三维图谱成像,为生物组织、微纳材料等复杂形貌样品的化学表征提供了新的有效途径。     

多光谱成像技术分析彩色艺术品的相关基础研究

多光谱成像技术集数字成像和光谱测量技术于一体,是一种记录光学信息的新型无损分析技术。基于对国内外文化遗产领域多光谱成像技术研究现状的分析,使用自行搭建的多光谱成像系统对敦煌壁画颜料模拟试板和现代国画在300~1000 nm范围内进行光谱图像采集,检验多光谱成像系统的适用性。结果显示多光谱图像能对外观相近的不同颜料做出快速区别,结合激光显微拉曼光谱技术,可进一步识别样品中颜料的种类;同时,多光谱图像还能够揭示具有紫外激发可见荧光特性的物质分布、画稿中的底稿信息、水渍痕迹等信息。实验表明多光谱成像技术可以有效获取彩色艺术品的多样化信息,在彩色艺术品研究领域具有良好的应用前景。     

基于Hadamard优化矩阵的多分辨显微关联成像研究

为满足显微成像领域的多样化需求,解决实际应用中成像质量与成像时间之间的矛盾,提出一种基于数字微镜器件的多分辨显微关联成像方法.该方法利用LED光源作为背景照射光源,对科研级荧光正置显微镜原光路改装设计为关联成像光路,采用多分辨Hadamard优化矩阵作为数字微镜器件的预置图样,实现了生物组织样品的连续多分辨成像.实验结果表明,多分辨显微关联成像系统的分辨率可达218 nm,单组测量后可同时输出8组不同分辨率图像,能够根据实际应用中不同图像质量需求选择不同的分辨率,减少成像时间和存储空间,极大地提高了显微成像的灵活性.这种新型多分辨显微关联成像方法可以扩展至细胞筛选、细胞实时成像等领域,对推动关联成像在细胞和生物组织显微成像领域的应用具有重要意义.     

Effective point-spread function for fast image modeling and processing in microscopic imaging through turbid media

An effective point-spread function (EPSF) for microscopic imaging through turbid media is proposed and calculated. The EPSF incorporates the property of a microscope system as well as the scattering property of a turbid medium. We prove that the image of a thin object embedded in a turbid medium can be expressed by the convolution of the EPSF with an object function. With the help of the convolution relation, image modeling for 5, 000, 000 incident photons can be approximately 15 times faster than the direct Monte Carlo simulation method for a one-dimensional object and can be at least 2 orders of magnitude faster for a two-dimensional object.     

Simulation of coherent properties of photons in scattering medium for optical coherence tomography

Monte Carlo model of optical coherence tomography is developed for simulation of photon transport in half infinite homogenous media. The procedure is accelerated by scaling the baseline data from standard Monte Carlo calculation in turbid media with arbitrary optical parameters. Gaussian beam is modeled by hyperboloid of one sheet for actual condition to obtain distribution of photons on sample surface. Depth dependence coherent signal and photons distribution are calculated in this way, which is important to reconstruction of optical parameters by inverse Monte Carlo. Numerical results have verified this method in turbid medium of different optical parameters with acceptable relative errors.     

蒙特卡罗模拟光通过大气后的时间分布

采用蒙特卡罗方法模拟了光通过光学特性参数不同的大气后透射光时间分布。分析了大气的散射系数、吸收系数、不对称因子及折射率对透射光时间分布的影响。结果表明：透射光时间分布曲线存在两个峰,分别对应子弹光与漫射光。各光学参数界定了子弹光、蛇形光、漫射光的大小和时间范围,并从统计模拟的角度解释了折射率大的大气中难以成像的原因。     

蒙特卡罗模拟光通过大气后的时间分布

采用蒙特卡罗方法模拟了光通过光学特性参数不同的大气后透射光时间分布.分析了大气的散射系数、吸收系数、不对称因子及折射率对透射光时间分布的影响.结果表明:透射光时间分布曲线存在两个峰,分别对应子弹光与漫射光.各光学参数界定了子弹光、蛇形光、漫射光的大小和时间范围,并从统计模拟的角度解释了折射率大的大气中难以成像的因为.     

Fast perturbation Monte Carlo method for photon migration in heterogeneous turbid media

We present a two-step Monte Carlo (MC) method that is used to solve the radiative transfer equation in heterogeneous turbid media. The method exploits the one-to-one correspondence between the seed value of a random number generator and the sequence of random numbers. In the first step, a full MC simulation is run for the initial distribution of the optical properties and the "good" seeds (the ones leading to detected photons) are stored in an array. In the second step, we run a new MC simulation with only the good seeds stored in the first step, i.e., we propagate only detected photons. The effect of a change in the optical properties is calculated in a short time by using two scaling relationships. By this method we can increase the speed of a simulation up to a factor of 1300 in typical situations found in near-IR tissue spectroscopy and diffuse optical tomography, with a minimal requirement for hard disk space. Potential applications of this method for imaging of turbid media and the inverse problem are discussed.     

Label-Free Microscopic Imaging Based on the Random Matrix Theory in Wavefront Shaping

Wavefront shaping technology has mainly been applied to microscopic fluorescence imaging through turbid media,with the advantages of high resolution and imaging depth beyond the ballistic regime. However, fluorescence needs to be introduced extrinsically and the field of view is limited by memory effects. Here we propose a new method for microscopic imaging light transmission through turbid media, which has the advantages of label-free and discretional field of view size, based on transmission-matrix-based wavefront shaping and the random matrix theory. We also verify that a target of absorber behind the strong scattering media can be imaged with high resolution in the experiment. Our method opens a new avenue for the research and application of wavefront shaping.     

Revisit to the symmetry relations in diffusely backscattered polarization patterns of turbid media

As there exists an inconsistency in claiming the symmetrical relations in the 16 Mueller matrix elements used to describe a turbid medium, the author restudies the symmetrical relationships between diffusely backscattered polarization patterns in isotropic turbid media and simulates all two-dimensional elements of diffusely backscattered Mueller matrix in both cases of Rayleigh and Mie scatterings using the doublescattering approximation and the Monte Carlo algorithm, respectively. The previous experimental observatious are compared with the numerically determined matrix elements, showing a good agreement in both double-scattering model and Monte Carlo simulation. The symmetrical relations between the Mueller matrix elements are clarified.     

电子回旋共振放电电离特性的PIC/MCC模拟

A theoretical and computational model is presented to study the ionization of the argon electron cyclotron resonance(ECR)microwave discharge using a quasi-three-dimensional electromagnetic particle-in- cell plus Monte Carlo collision method.The interaction between the charged particles and microwave fields are described by the electromagnetic mode of particle-in-cell method.The collision processes are treated with Monte Carlo method.The simulation code is the original work.The results of the particle simulation for the ECR discharge of argon gas which include the microscopic features of charged particles and the electromagnetic characteristics of the ECR discharge plasma,and also the transient phenomena have been presented.     

Time-gated optical imaging through turbid media using stimulated Raman scattering: Studies on image contrast

In this paper, we report the development of experimental set-up for time-gated optical imaging through turbid media using stimulated Raman scattering. Our studies on the contrast of time-gated images show that for a given optical thickness, the image contrast is better for sample with lower scattering coefficient and higher physical thickness, and that the contrast improves with decreasing value of anisotropy parameters of the scatterers. These results are consistent with time-resolved Monte Carlo simulations.