Atomic contrast transfer in annular darkfield images

We examine some of the assumptions underlying the standard optical equation as used for modelling high-resolution annular darkfield (Z-contrast) images of thin specimens. The validity of the approximations (i) that scattering occurs as spherical waves (atoms are point potentials) and (ii) that the depth of focus is infinite is found to be resolution-dependent. The correction to the optical equation for non-spherical wave scattering is found to be important when the probe size is of the order of 0·1 nm or smaller, and does not vanish in the ideal case of a large annular detector with no hole. Depth of focus becomes an important consideration at 100 kV for probes smaller than about 0·2 nm when the specimen thickness exceeds 10 nm. Both corrections can significantly degrade the effective point-to-point resolution of high-resolution Z-contrast images relative to that predicted by the standard optical equation.     

球形金纳米颗粒的消光特性及不同折射率环境下的共振波长

为了研究球形Au纳米颗粒的消光特性及共振波长与环境折射率的关系,采用Mie理论计算了直径为20,40,60和80nm的球形Au纳米颗粒在不同折射率的介质环境中的消光谱,并利用消光法实验测量了这4种粒径的Au纳米颗粒在不同浓度糖水中的吸光度,取得了糖水介质环境的折射率与浓度之间的关系及其色散规律,以及Au纳米颗粒的消光系数及共振波长随环境折射率变化的数据。结果表明,介质环境糖水浓度一定时,Au颗粒半径增大,消光峰值红移;颗粒半径一定时,周围介质环境糖水浓度增大,消光峰值红移;Au纳米颗粒的共振波长与糖水浓度呈线性关系,20,40,60,80nm的Au纳米颗粒对应的线性斜率分别为0.106 0,0.135 5,0.193 8,0.265 8,斜率随粒径尺寸的增大而增大。该结论为探索纳米颗粒的折射率敏感性奠定了基础。     

Three-dimensional automated nanoparticle tracking using Mie scattering in an optical microscope

The forward scattering of light in a conventional inverted optical microscope by nanoparticles ranging in diameter from 10 to 50nm has been used to automatically and quantitatively identify and track their location in three-dimensions with a temporal resolution of 200ms. The standard deviation of the location of nominally stationary 50-nm-diameter nanoparticles was found to be about 50nm along the light path and about 5nm in the plane perpendicular to the light path. The method is based on oscillating the microscope objective along the light path using a piezo actuator and acquiring images with the condenser aperture closed to a minimum to enhance the effects of diffraction. Data processing in the time and spatial domains allowed the location of particles to be obtained automatically so that the technique has potential applications both in the processing of nanoparticles and in their use in a variety of fields including nanobiotechnology, pharmaceuticals and food processing where a simple optical microscope maybe preferred for a variety of reasons.     

用光透消光法测定颗粒物质的折射率

基于Ｍｉｅ光散射理论及Ｌａｍｂｅｒｔ—Ｂｅｅｒ光透射定律,本文提出一种测定颗粒状物质的折射率的有效方法──光透消光法。本文给出了测量原理、方法及对几种标准颗粒折射率的实测结果     

LiNbO3外调制器的10 Gbit/s光纤传输系统

建立了一个10Gbit/s光纤传输系统平台,实现了10G光信号无中继、无误码传输,系统采用了NRZ码、高性能的GaInAsP多量子阱DFB激光器、LiNbO₃电光调制器。进行了系统的传输实验,得到了系统的各项指标参数,分析了影响系统传输质量的因素,研究了传输系统中的一些关键问题。无中继距离为84km,采用了CWDM技术对信号进行复用。在误码率为10^-12时,接收机的最小接收光功率可达到-26.76dBm。系统的功率代价为0.49dB,没有出现误码率平台。实验还对发送光信号的消光比与接收机灵敏度之间的关系进行了研究,连续观察24h无误码。     

Axial Phase-Darkfield-Contrast (APDC), a new technique for variable optical contrasting in light microscopy

Axial phase-darkfield-contrast (APDC) has been developed as an illumination technique in light microscopy which promises significant improvements and a higher variability in imaging of several transparent 'problem specimens'. With this method, a phase contrast image is optically superimposed on an axial darkfield image so that a partial image based on the principal zeroth order maximum (phase contrast) interferes with an image, which is based on the secondary maxima (axial darkfield). The background brightness and character of the resulting image can be continuously modulated from a phase contrast-dominated to a darkfield-dominated character. In order to achieve this illumination mode, normal objectives for phase contrast have to be fitted with an additional central light stopper needed for axial (central) darkfield illumination. In corresponding condenser light masks, a small perforation has to be added in the centre of the phase contrast providing light annulus. These light modulating elements are properly aligned when the central perforation is congruent with the objective's light stop and the light annulus is conjugate with the phase ring. The breadth of the condenser light annulus and thus the intensity of the phase contrast partial image can be regulated with the aperture diaphragm. Additional contrast effects can be achieved when both illuminating light components are filtered at different colours. In this technique, the axial resolution (depth of field) is significantly enhanced and the specimen's three-dimensional appearance is accentuated with improved clarity as well as fine details at the given resolution limit. Typical artefacts associated with phase contrast and darkfield illumination are reduced in our methods.     

动态线偏振光散射纳米颗粒粒度测量法的研究与分析

多重散射是传统动态光散射法测量纳米颗粒溶液浓度上限受到限制的主要原因。为此文中提出了动态线偏振光散射纳米颗粒粒度测量法,通过改变颗粒入射光和散射光的偏振状态,降低颗粒间多重散射的影响。现利用Mie散射理论分析了入射光与散射光偏振状态之间的关系,并通过实验方法探知偏振光在散射介质中的传输特性,揭示了在动态光散射中使用垂直偏振光作为入射光的实验依据。最后对动态线偏振光散射颗粒测量法和传统光子相关光谱测量法进行了实验及分析,通过两种方法的比较,验证了上述理论的正确性。     

基于纳米颗粒的近场光场多分量表征技术

近场光学主要探索光波长以内的近场区域的光学现象,是一门研究光与物质在纳米尺度相互作用的学科。近场光场区域内会产生如自旋轨道耦合等诸多独特的物理现象,是光学领域的研究热点,对其进行精确的表征有助于相关物理现象的探究。然而,近场光场较强的束缚性和复杂的矢量性使近场光学表征技术成为该领域研究的难点和热点。典型的近场扫描光学显微技术采用近场探针探入到近场区域从而收集近场光信息,可以在一定程度上解决束缚性的问题。但是其复杂的矢量性需要设计独特的近场探针来实现不同光场分量的探测,相应的探针也需要纳米尺度的结构设计和昂贵复杂的半导体微纳加工工艺作为保证。本文着重介绍关于利用纳米颗粒作为近场探针的新型近场光场多分量表征技术的一系列工作。纳米颗粒是圆对称结构,理论上可以响应所有近场分量。依据米散射理论可以通过对颗粒材质、尺寸的设计,表征所需近场分量,包括面内、面外的光频电场、磁场等分量,并且通过对这些分量的精确测量,还可以对近场区域内自旋分量、轨道自旋耦合、光学拓扑结构等进行精确地表征。该类方法使用的近场探针易于制造,具有低成本、无需复杂控制系统等优势,为近场光学的研究提供了一种高效的表征手段。     

应用于显示光学中的偏振分束棱镜的研制

介绍了一种用于硅基液晶光学系统的薄膜型偏振分束棱镜的研制,其中膜系由三种膜料56层膜层构成,文中介绍了设计结果及其制作工艺,并对其测试系统进行了简要说明,测试了制作样品,对测试结果和设计值进行简要分析,结果表明该偏振分束棱镜实现了大角度、宽波段、高消光比的要求。     

Microspectroscopic measurement of the optical properties of rat liver in the visible region

Microspectroscopy is used to investigate optical properties of haemoglobin-free perfused rat liver. Visible spectra of 20 μm diameter spot size were measured in transmission and/or reflection modes as a function of the thickness (< 1200 μm) of the liver-edge. Optical density (OD) in transmission mode increased with the increasing liver thickness, whereas in reflection mode OD decreased but became almost constant above a certain thickness (c. 600 μm) of the liver. The Kubelka-Munk (KM) two-flux model, with a minor modification, was applied successfully to the analysis of the changes in OD as a function of the thickness. This approach estimates the KM absorption coefficient (E_KM), KM scattering coefficient (S_KM) and effective penetration depth (δ_eff) of the liver. The optical properties were similar to reported values, obtained with different methods.     

Variable bright-darkfield-contrast, a new illumination technique for improved visualizations of complex structured transparent specimens

Variable bright-darkfield contrast (VBDC) is a new technique in light microscopy which promises significant improvements in imaging of transparent colorless specimens especially when characterized by a high regional thickness and a complex three-dimensional architecture. By a particular light pathway, two brightfield- and darkfield-like partial images are simultaneously superimposed so that the brightfield-like absorption image based on the principal zeroth order maximum interferes with the darkfield-like reflection image which is based on the secondary maxima. The background brightness and character of the resulting image can be continuously modulated from a brightfield-dominated to a darkfield-dominated appearance. When the weighting of the dark- and brightfield components is balanced, medium background brightness will result showing the specimen in a phase- or interference contrast-like manner. Specimens can either be illuminated axially/concentrically or obliquely/eccentrically. In oblique illumination, the angle of incidence and grade of eccentricity can be continuously changed. The condenser aperture diaphragm can be used for improvements of the image quality in the same manner as usual in standard brightfield illumination. By this means, the illumination can be optimally adjusted to the specific properties of the specimen. In VBDC, the image contrast is higher than in normal brightfield illumination, blooming and scattering are lower than in standard darkfield examinations, and any haloing is significantly reduced or absent. Although axial resolution and depth of field are higher than in concurrent standard techniques, the lateral resolution is not visibly reduced. Three dimensional structures, reliefs and fine textures can be perceived in superior clarity.     

雾和气溶胶前向散射对消光的影响

光电工程中探测器接收的光强包括透射光和大气前向散射光。雾和大气气溶胶粒子的前向散射增强了透射光,从而导致测量的衰减比实际衰减小。本文采用Mie散射理论,根据气溶胶谱分布以及雾滴的谱分布模型及其与能见度的经验关系,计算了可见光到中波红外波长的前向散射修正因子。详细分析了激光在气溶胶和雾衰减中前向散射修正因子随粒子平均半径、能见度和波长等参数的变化关系,并拟合出前向散射修正因子随粒子平均半径和视场乘积的经验关系式,在10°视场内平均残差小于0.02,可为相关光电工程提供参考。     

基于共焦成像法的亚表层损伤散射仿真

光学零件的亚表面缺陷直接影响其使用性能和抗激光损伤阈值等重要指标,而造成这些危害的根本原因是由损伤层引入的入射光的散射。采用时域有限差分(FDTD)法,结合共焦层析测量系统进行模拟仿真。首先,针对常见的光学材料,分析了入射光经由亚表层中的微裂纹、气泡等常见缺陷调制后的光场分布,并结合不同形态参数和光学参数建立模型;其次,引入球面波激励源,模拟计算了入射波聚焦点沿固定间隔逐渐偏离缺陷时的散射分布。结果表明:共焦层析测量系统能够实现对亚表层损伤的测量,满足纵向响应函数趋势。     

基于无散射参照偏振成像技术的水下目标光学检测（英文）

光学偏振成像系统能够基于水体散射噪声与目标信号之间的退偏振特性差异有效地抑制光散射效应对水下目标检测效果的影响。然而,传统偏振检测方法需要事先在图像无目标区域对水体后向散射光的偏振度进行测量,并且假设目标为完全非偏振特征。当水体后向散射场景没有呈现在光学成像系统视场中或者目标具有偏振明显特性时,上述检测方法失效。针对该问题,通过测量水下场景的平行偏振与正交偏振分量,提出了偏振减方法对水体散射噪声与目标信号的退偏振特性进行正确估计,并且在石英比色皿容器中对所提方法的可靠性进行了实验验证。结果表明,偏振减方法适用于无散射背景参照的情形,并可以检测水下环境中表面光滑的保偏目标。     

分布式光纤测温系统

在分析和研究喇曼分布式光纤测温系统原理的基础上，完成了喇曼分布式光纤测温系统的结构设计，并在此基础上成功地开发出了实验系统，从而顺利地完成了温度传感实验任务。