A proximate method for determining the refractive indices of liquids

A simple method for measuring the refractive index of liquids that fill thin-wall cylindrical cells of any diameter is described. The method is based on the light-refraction phenomenon in cylindrical lenses and is implemented using a system of lines that are regularly positioned in a plane and are observed in monochromatic light through a liquid-filled cylinder. Images of lines are turned relative to the initial orientation, and the rotation angle is unambiguously related to the refractive index of the liquid.     

Electron energy dependence of characteristics of fluorescent plates for ultrahigh-voltage electron microscopes

The characteristics of fluorescent plates for high energy electron beams (0.5-2.0 MeV) are examined. The thickness and the optical transparency of plates strongly affect the luminous broadening and intensity. The spatial luminous broadening in fluorescent plates is measured and is simply represented by the rise width of a knife edge image. When the thickness is much smaller than the range of incident electrons, the rise width is 1/4-1/5 of the thickness in the case of YAG single crystal plates that are transparent for light, while the rise width is nearly equal to the thickness for the packed P22 powder plates that are opaque for light. To suppress the luminous broadening under 50 microm, the thickness of YAG plates has to be thinner than 250 microm in the energy region around 2 MeV. Under the same condition of the rise width, the luminous intensity of YAG plates is twice as high as that of the P22 plates.     

微注塑保压时间对平面透镜相对折射率的影响

针对透明器件对光学性能要求很高的现实，提出通过调控相对折射率来实现光学性能调控的方法。以微注塑薄壁透镜为例，对平行激光光源通过光学透镜后的波阵面进行检测与重建;接着推导出了波阵面检测结果与相对折射率的理论关系，并计算了透镜内部相对折射率的分布;最后考查了微注塑过程中保压时间对透镜相对折射率分布的影响。实验结果表明：当微注塑保压时间从1s延长至3s时,相对折射率分布均匀度明显提高，折射率的极差从6.1×10-3减小到2.9×10-3。该相对折射率表征方法能有效调控光学制品性能。     

UV-reflecting wing scales in the silk moth Antheraea assamensis: its biophysical implications

Scanning electron microcopy of the wing scales from some specific locations in the silk moth, Antheraea assamensis, revealed the presence of 50-60-nm-thick microridges and 80-nm-thick air spaces between them. The principle of optics suggests that when the measured average thickness of microridges or lamellae is about 50-60 nm, that of the air-space between them is about 80-82 nm, then due to the known refractive index of air (1.0) and the infrared refractive index of lamellar cuticle (1.60), the lamellae (microridges) and the intervening lamellar air spaces will have similar optical thickness. A common optical thickness for the two types of layers causes the microridge structures to function in the fashion of a quarter wavelength interference filter and to reflect UV light. Behavioral studies under the natural conditions and short experimental exposure of the moths to artificial UV light suggests that coupling behavior of the moth is governed to a significant extent by these UV-reflecting wing scales. The importance of the study in overcoming a major problem of low autocoupling efficiency of moths in the Muga Silk Industry is discussed with the help of relevant literature.     

A new high-aperture glycerol immersion objective lens and its application to 3D-fluorescence microscopy

High‐resolution light microscopy of glycerol‐mounted biological specimens is performed almost exclusively with oil immersion lenses. The reason is that the index of refraction of the oil and the cover slip of ~1.51 is close to that of ~1.45 of the glycerol mountant, so that refractive index mismatch‐induced spherical aberrations are tolerable to some extent. Here we report the application of novel cover glass‐corrected glycerol immersion lenses of high numerical aperture (NA) and the avoidance of these aberrations. The new lenses feature a semi‐aperture angle of 68.5°, which is slightly larger than that of the diffraction‐limited 1.4 NA oil immersion lenses. The glycerol lenses are corrected for a quartz cover glass of 220 µm thickness and for a 80% glycerol‐water immersion solution. Featuring an aberration correction collar, the lens can adapt to glycerol concentrations ranging between 72% and 88%, to slight variations of the temperature, and to the cover glass thickness. As the refractive index mismatch‐induced aberrations are particularly important to quantitative confocal fluorescence microscopy, we investigated the axial sectioning ability and the axial chromatic aberrations in such a microscope as well as the image brightness as a function of the penetration depth. Whereas there is a significant decrease in image brightness associated with oil immersion, this decrease is absent with the glycerol immersion system. In addition, we show directly the compression of the optic axis in the case of oil immersion and its absence in the glycerol system. The unique advantages of these new lenses in high‐resolution microscopy with two coherently used opposing lenses, such as 4 Pi‐microscopy, are discussed.     

2,2'-thiodiethanol: a new water soluble mounting medium for high resolution optical microscopy

The use of high numerical aperture immersion lenses in optical microscopy is compromised by spherical aberrations induced by the refractive index mismatch between the immersion system and the embedding medium of the sample. Especially when imaging >10 micro m deep into the specimen, the refractive index mismatch results in a noticeable loss of image brightness and resolution. A solution to this problem is to adapt the index of the embedding medium to that of the immersion system. Unfortunately, not many mounting media are known that are both index tunable as well as compatible with fluorescence imaging. Here we introduce a nontoxic embedding medium, 2,2'-thiodiethanol (TDE), which, by being miscible with water at any ratio, allows fine adjustment of the average refractive index of the sample ranging from that of water (1.33) to that of immersion oil (1.52). TDE thus enables high resolution imaging deep inside fixed specimens with objective lenses of the highest available aperture angles and has the potential to render glycerol embedding redundant. The refractive index changes due to larger cellular structures, such as nuclei, are largely compensated. Additionally, as an antioxidant, TDE preserves the fluorescence quantum yield of most of the fluorophores. We present the optical and chemical properties of this new medium as well as its application to a variety of differently stained cells and cellular substructures.     

用光纤面板和数字存储电路实现单液晶光阀彩色图像的投影显示技术

本文介绍了一种利用三原色通道光纤面板和数字存储电路光电结合的图像信息处理技术,实现单液晶光阀彩色电视图像的大屏幕投影显示系统,设投影显示系统具有结构简单、调试方便、性能价格比高的优点。     

The use of a digitizing frame store in microscopy

A digitizing frame store giving real time read out of the image for TV or slow scan rates is now available. This equipment has a number of applications in both optical and electron microscopy. Examples of results obtained by linkage to a low light level TV system are given showing that use of the frame store yields image information not otherwise available. Other possibilities of the system are indicated.     

New high-DQE imaging plate scanner using the reflected readout laser signal for noise corrections

Imaging Plates (IPs) are in principle ideal electron detectors combining a large active layer area with a high sensitivity, linear dynamic range detection over 5 orders of magnitude. A moderate resolution and a decreasing detection quantum efficiency (DQE) for higher electron doses limit their use so far. The decrease of the DQE results from linear noise contributed by readout laser instabilities and inhomogeneities of the IP active layer. Here we present data on a new IP drum scanner prototype. This scanner combines twin channel amplification electronics with a new type of readout laser which allows a smaller readout focus and increased stability. The current nominal pixel size is 25 microm, and the measured modulation transfer function (MTF) indicates that further reduction of the scanning step size down to pixel sizes in the range of 12-15 microm should be possible. A unique feature of the new scanner is the simultaneous recording of the reflected readout laser light. The reflected light signal can be used for a posteriori alignment of repeated scans of one individual IP and for a correction of one part of the high spatial frequency noise contribution (reflected light correction). The posteriori alignment now allows an easy conventional gain normalization of the luminescence signal without using special markers on the IP. Both corrections lead to an increase of the DQE for high electron doses.     

光谱共焦位移传感器镜头设计研究

光谱共焦位移传感器是一种高精度、非接触式位移传感器。本文讨论了光谱共焦法用于位移测量的基本原理,用Zemax光学设计软件完成了一个镜头组的设计,并给出了光谱共焦位移传感器镜头组的设计方法以及像差分析。该镜头组采用密接透镜结构,工作波段为486.13nm-656.27nm,测量范围约为91μm,轴向响应FWHM优于5μm。通过线性回归分析得出波长与位移间判定系数为0.99523,在测量范围内,位移与波长间的线性关系较好。     

A television system for point counting morphometry in high resolution light microscopy

High resolution light microscopical images that can be superimposed on a test system for the estimation of stereological parameters are obtained by a television system modified for point-counting morphometry. The full resolving power of the light microscope is exploited and a test system applied in the same plane as the microscopical image displayed on the monitor screen. Volume fraction estimates of nuclei and zymogen granules from the rat pancreas made with the television microscopical system and with electron-microscopic micrographs rendered the same precision, and showed that the volume fraction of objects as small as zymogen granules was measurable with the light microscope. The measuring with the television microscopical system was about 15 times faster than with electron-microscopic micrography and about 5 times faster than with conventional photomicrography and the light microscope.     

Note: Refractive index sensing of turbid media by differentiation of the reflectance profile: Does error-correction work?

A widely used method for determining refractive index postulates that the derivative of the angular profile for light reflected from the sample is maximum at the critical angle for total internal reflection (TIR). It is well-known that in turbid media this "differentiation method" yields errors in refractive index. Unexplained anomalies in previous error-calculations are eliminated if one uses a recent model of TIR which departs from traditional Fresnel theory. However we find that, in practical situations, the refractive index obtained by differentiation even after error-correction is significantly different from the best estimate for the refractive index obtained by curve-fitting the reflectance data. Thus the differentiation method lacks scientific validity in turbid media.     

Short note on parallel illumination in the TEM

Parallel illumination conditions are required for several experiments in the transmission electron microscope (TEM). The image rotation induced by the helical trajectory of electrons passing through the magnetic field of the TEM lenses inevitably induces an inclination of the beam relative to the optical axis in the object plane--even for an electron which travels parallel to the optical axis in the far field. This angle (shear angle) is vectorially added to the convergence angle; it depends both on the distance to the optical axis and the magnetic field. By using a beam tilt compensation method, the minimum shear angle is found to be of the order of 1 mrad for a field of view of 2 microm in a 200 kV TEM. In practice, "parallel illumination" can only be obtained for fields of view 1 microm.     

高对比度低压驱动全息聚合物分散液晶光栅

为了降低全息聚合物分散液晶光栅的驱动电压并提高其对比度,基于偏振原理设计了一种新型电调谐光栅。对传统的全息聚合物分散液晶(HPDLC)光栅进行了基板表面取向处理,加强液晶的均一排列程度,消除了液晶区域内的散射;然后,在光栅前面放置扭曲向列(TN)偏振调谐器,通过调节入射光的偏振方向,实现光栅内液晶折射率的变化,进而改变与聚合物折射率的差别,实现衍射强度的调谐。实验结果表明:光栅的阈值电压降低到了0.75～0.8V,对比度提高到了245:1,是传统HPDLC光栅的6～7倍,同时也大幅降低了散射损失且稳定性良好,可满足高端光学设备及显示产品方面的需求。     

Electron-electron interactions in cathode objective lenses

The impact of electron-electron interactions on the electron-optical performance of imaging cathode objective lenses is evaluated. Three types of cathode objectives are considered: decelerating and accelerating electrostatic, and combined magnetic lenses. The beam blur is calculated for field sizes ranging from 50 microm x 50 microm to 500 microm x 500 microm and total beam currents ranging from 200 nA to 20 microA. The functional dependence of the beam blur upon electron beam current and current density is elucidated in detail.     

Tomographic reconstruction of the cross-sectional refractive index distribution in semi-transparent,birefringent fibres

Optical diffraction tomography (ODT) is used to reconstruct the complex refractive index distribution in cross-sections of semi-transparent, birefringent fibres. The selected fibres were polymer and animal fibres of either circular or non-circular cross-section with average thicknesses in the range 8–110 μm. This choice of samples was made to illustrate the imaging capabilities of ODT, and also to demonstrate some potential applications of the technique. The images representing the reconstructed refractive index distributions have a spatial resolution of about 2 μm, and show noticeable image contrast for refractive index variations of about 0·001. The ODT reconstructions compare well with refractive index information provided with the samples, and with scanning electron micrographs of cross-sections of the same fibre samples. From these results it appears that ODT can be used to reconstruct the complex refractive index distribution in cross-sections of semi-transparent, birefringent fibres.     

A modification of the ET secondary electron detector with a single crystal scintillator

On the basis of the study of optical properties of single crystal YAG scintillators, it has been found that the maximum light output signal propagated in the required direction in the scintillator of a secondary electron detector is obtained if a cone-shaped scintillator is used. A modified Everhart-Thornley (ET) detector containing a conical scintillator and an electro-optical diaphragm operated at a positive voltage shows an increase to 2.8 times the light output signal of the classical ET detector with a flat single crystal YAG scintillator disc. The modification allows optimization of the suction of secondary electrons toward the scintillator and of the propagation of light from the scintillator toward the light guide.     

Fabrication and characterization of rugate structures composed of SiO_2 and Nb_2O_5

1Introduction Opticalcoatingdesignsbasedonlayers,whichareinhomogeneousalongthestackaxis,haveopticalandmechanicalpropertiesthatdiffer fromthoseofconventionalhigh low index stacks.Particularly,thewideaccessibleangular rangeandthelowopticalscatterlevelmake themsuperiortotraditionalstackswithrespect toselectedpurposessuchasomni directionalde vicesornotchfilters[14].Manufacturingsuch systemsinpracticerequiresthecalculation,dep osition,monitoringandcharacterizationofopti calcoatingswithawelldefinedc…     

测量自聚焦光纤透镜聚焦常数的曲线拟合算法

提出了基于曲线拟合的光纤透镜聚焦常数的测试方法,用于超小自聚焦光纤探头研制过程中聚焦常数的直接测试。基于自聚焦光纤透镜模型及其折射率分布特征,研究了测量自聚焦光纤透镜聚焦常数的二次多项式拟合和线性化拟合算法。论述了聚焦常数对超小自聚焦光纤探针传光性能的影响。利用光纤端面折射率测试仪测试自聚焦光纤的折射率分布轮廓曲线,根据二次多项式拟合和线性化拟合算法分别求得聚焦常数和中心折射率。实验结果显示,利用二次多项式拟合算法和线性拟合算法求出的聚焦常数分别为5.587mm-1和5.513mm-1,与厂家的标称值5.5mm-1基本吻合,表明曲线拟合算法适用于对自聚焦光纤透镜聚焦常数的测量与分析。     

角度位置自动识别的红外折射率测量

为准确快速获得块体硫系玻璃红外波段的折射率,搭建了基于类准直测量法的折射率测量系统。该系统采用液氮制冷的碲镉汞探测器和特殊的光路实现了光强信息的高分辨采集,使用高分辨数据采集卡将角度信息数字化,利用精密步进电机传动控制系统实现了光强信号与位置信号的同步记录。开发的测量软件可自动判别光强峰位信息,自动计算获得待测样品的折射率。对比测试Ge_(20)Sb_(15)Se_(65)、Ge_(28)Sb_(12)Se_(60)、As_2S_3和As_2Se_3商用硫系玻璃在3.39μm和4.8μm处的折射率。实验结果表明,该装置系统测量折射率的标准偏差为10~(-3),测量不确定度为0.002 9,可快速、准确测量块体材料红外波段的折射率。