基于旋转扫描探头的OCT内窥成像系统设计

为了同时获取样品的表面和深度信息,研究光学相干层析的成像原理,建立了基于光学相干层析技术的内窥系统,实现了旋转扫描成像,系统的工作波长为1 310 nm,工作带宽为80 nm.理论推导及计算机仿真得到了系统信噪比与干涉仪的分光比、反射率之间的关系并分析了理论分辨率和探测深度.提出外径为5 mm的内窥镜扫描探头,聚焦距离为12 mm,数值孔径NA为0.47,折射率分布常量A=0.218 7.利用微型电机驱动直角棱镜实现扫描,旋转速度为25 rpm,旋转一周得到640个采样点.采用多层盖玻片和洋葱表皮作为样品进行实验分析,得到了盖玻片和洋葱的图像,横向分辨率和纵向分辨率分别为10 μm和15 μm.结果表明,设计的光学相干层析内窥系统能够用于旋转扫描成像,获取更多的组织信息.     

Fourier analysis based phase shift interferometric tomography for three-dimensional reconstruction of concentration field around a growing crystal

The present work is concerned with the three-dimensional reconstruction of concentration field around a crystal growing from its aqueous solution using Fourier analysis based phase shift interferometric tomography. Projection data of convective field around a growing NaClO₃ crystal have been recorded using a Mach–Zehnder interferometer. A new numerical method based on the concept of real time phase shift interferometry has been employed for the analysis of the interferograms. By interpreting the interferograms as projection data, the 3-D distribution of salt concentration has been determined using principles of tomography. Study shows that the Fourier analysis-based phase shift method is a novel approach for crystal growth studies as it requires only one interferometric image for the determination of full phase information as opposed to the conventional real time phase shift interferometry wherein at least three or more phase-shifted interferograms are needed. Results have been presented in the form of interferograms, path-integrated concentration contours and three-dimensional concentration profiles over select horizontal planes above the growing crystal. Based on the reconstruction results, distribution of salt concentration in the crystal vicinity is determined and an appropriate mechanism of buoyancy-induced fluid movement in the growth chamber is discussed.     

光学相干层析成像系统中双通快速扫描光学延迟线的数值分析

以matlab为工具,详尽分析双通快速扫描光学延迟线在最佳耦合条件下的光束传输与分布,为双通快速扫描光学延迟线的设计、元件选择和系统调整提供理论依据.得出离焦距离Δf=1μm和Δf=578 μm两个理论上的最佳耦合点.但就实际光路调试来看,离焦距离Δf=1 μm为此系统的最佳耦合点.     

利用网络理论进行电阻抗层析成像中的多分辨率技术

首先讨论利用网络理论进行电阻抗层析成像的基本原理，并给出了节点导纳知阵所应服从的两个基本约束．为了加速和改进算法，提出了多分辨率的算法．按照这一算法，首先将被测物体离散化为较大的单元，先在粗分辨率下进行求解，利用所得的结果作为估计的初值，再进行下一级较细分辨求解．计算机模拟结果表明，利用多分辨率技术可以加快收敛，减小误差．     

Spatial and temporal resolution in cryo-electron microscopy—A scope for nano-chemistry

Cryo-electron microscopy has evolved in an established approach to study the structure of bio-colloids. Recent developments in instrumentation and automation, often demanded by life sciences, made cryo-EM a general tool in colloid chemistry. Recently improved instrumentation for vitrification has resulted in reliable and reproducible preparation of specimen in water and other solvents. A dynamic approach, following processes in time is gaining importance and a time resolution up to 1 ms is expected to become general available. With improved instrumentation and automation 3D reconstructions by cryo-EM tomography are becoming routinely accessible. Tomography as such or in conjunction with time resolved microscopy is expected to give new insights in (macro)molecular assembly/disassembly mechanisms and thus become an essential tool in nano-chemistry.     

Inversion formula and singularities of the solution for the backprojection operator in tomography

Let , , be the backprojection operator. The range of this operator as an operator on non-smooth functions is described and formulas for are derived. It is proved that the operator is not injective on but is injective on the subspace of which consists of even functions . Singularities of the function are studied. Here is a piecewise-smooth compactly supported function. Conditions for to have compact support are given. Some applications are considered.

     

Optical tomography of the laser's Gaussian electric field

A method for the measurement of the spatial distribution of birefringence, caused by intense femtosecond laser pulses in condensed plasma, is presented for the case of a Gaussian laser beam. For that only two light intensities are to be measured on the probe beam in a polariscope.     

基于CT技术的古琴琴腔构造无损检测研究

古琴的材质特性及制作工艺影响着古琴的品质,同时古琴形制与琴腔布局关系到古琴工艺的完善与传承, 因此在不破坏古琴结构的前提下获取内部琴腔特征与参数十分重要。利用CT无损检测技术对古琴整体进行扫描,得到了琴腔构造断层图,从而研究了古琴面板木纹纹理、面板底板的连接方式和内部缺陷,并运用Mimics软件中的面绘制法实现了古琴琴腔构造的三维重建,使CT断层扫描图像由二维转换为三维立体,更加完整全面地展现古琴琴腔构造形态,最后获得古琴具体琴腔尺寸。实验研究表明,仲尼式与落霞式古琴琴腔构造差异显著,其中仲尼式琴腔表面起伏变化较大,落霞式琴腔表面趋于平缓;仲尼式琴腔体积小于落霞式,琴项位对比明显。通过利用CT无损检测技术实现了对古琴内部信息的准确获取,这对于探究古琴的制作工艺及质量检测起到重要的技术支撑作用,同时也为其他传统珍贵器具内部结构的无损研究提供参考依据。     

基于哈特曼波前探测层析重建折射率场

介绍了哈特曼层析测量系统的原理,设计静态测试实验,对实际圆对称折射率场分布进行了层析重建.系统由哈特曼采集折射率场的投影数据,采用代数重建算法进行层析重建,取得了满意的重建结果.     

Pulsed TV holography and tomography for the study of transient waves in air

Transient waves in air are recorded and reconstructed using pulsed TV holography and computerized tomography (CT). Experiments are performed with an electrical discharge between two electrodes as the acoustic wave source. The free space wave-fronts and pressure fields are reconstructed. Waves reflected and diffracted by different obstacles are also recorded and reconstructed in three dimensions. Speckle averaging and image processing techniques are used to get the high quality projection fields needed for CT reconstruction.