用强迫恢复法测量原子核自旋晶格弛豫时间 T_1

本文对强迫恢复法测量原子核的自旋晶格弛豫时间T_1进行了理论探讨和具体实验。该方法使用的脉冲序列有90°—[τ—90°,180°,90°]_n 及180°—[τ—90°,180°,90°]_n 二种。该方法的最大优点是比一般测量T_1的方法测量速度快,准确性较高。它适用于测量自旋晶格弛豫时间T_1及自旋自旋弛豫时间T_2都较长的样品,并可观察磁化矢量在z 方向(恒磁场H_0方向)上按指数恢复的过程。文中还讨论了用复合脉冲旋转坐标框架方法,克服磁化矢量旋转角度的误差,以提高测量精度。但该方法不适用于高分辨谱的各条谱线对应核的T_1测量。     

浅圆弧的铣削加工及误差分析

在立铣床上用圆柱立铣刀铣削圆弧零件,将立铣头旋转一角度α时,走刀方向与铣刀轴线成90°+α角,零件便加工为一椭圆弧面。这个椭圆弧面就是铣刀端面在走刀方向投影的一部分。设铣刀直径为φ,当铣刀轴线与走刀方向的夹角从90°～180°变化时,被铣削表面的曲率半径变化过程为∞～φ/2(见图1)     

实用新型浊度仪

浊度仪由传感器、放大器和显示器组成.传感器采用散射透射光度之比的测量方法和光电器件互补设计,浊度在0～400NTU的范围内,直接输出线性信号,线性度可调.放大器的输入采用绝对测量电路来提高测量浊度的精确度和稳定度,使仪器受环境温度、测量光束或器件老化的变化影响很小,浊度读数准确、稳定、线性范围宽,适用于污水、饮用水、地表水处理、水的循环利用及化工、石油、选冶、印染、造纸、制药、食品等各种液体的浊度测量.     

超光滑表面的微分散射测量

超光滑表面反射镜是激光陀螺中的关键器件，镜片的粗糙度引起的散射光直接影响陀螺的闭锁阈值，因而研究超光滑表面的加工和检测有着重要的应用价值。本文比较了超光滑表面的各种测试方法，提出了一种微分散射测量方法，用光子计数器作微弱散射光的接收器，测量散射平面内—90°～90°范围内的散射光强度分布，光子计数器的探测范围在10－11～10－16W，微分散射测量系统的测量重复精度为±10％。     

大气散射光与能见度理论关系的探讨

本文探讨了大气对光谱的散射特性及由散射引起的大气消光问题，介绍了利用测量大气对光的散射量来获得能见度值的理论和测量基理，并从大气Ｍｉｅ散射理论出发，对粒子散射光强与能见度间的数学关系进行了分析和推导。     

基于GRIN-Lens散射式红外浊度仪的设计

根据水质浊度测定标准ISO 7027-1:2016,结合散射法浊度测量原理,设计一种用于测量环境水体浊度的小型化便携式浊度仪。测量光源采用波长为880 nm的红外LED,设计了恒流源驱动电路提高光源的稳定性。浊度仪以嵌入式ARM处理器为核心,基于GRIN-Lens自聚焦透镜和TSL2581光强传感器设计检测模块,并通过OLED显示屏实时显示测量数据。设计并通过3D打印技术加工了机械装置,实现了包括光源、比色皿、检测器和GRIN-Lens等结构一体化的测量系统。实验结果表明,浊度仪在0～400 NTU的样品中可精确地对浊度进行测量,线性良好,精密度良好,方法检出限为0.2 NTU。     

基于AT89S52单片机的智能浊度仪

依据ISO7027测量水质浊度标准,设计了智能浊度测量仪.采用散射透射光度之比测量浊度,消除了因LED光源老化对测量准确度的影响,并选用AT89S52单片机作为主控制芯片,同时对透射和90°散射光信号进行放大和交替采样,把数据信号送入AT89S52进行信号处理和显示.对仪器进行模拟实验,实验证明仪器相关系数较好,浊度测量稳定可靠.     

埋头紧固件椭圆形表面裂纹应力强度因子的三维有限元分析

采用裂端为 2 0节点奇异单元的三维有限元模型 ,对工程中常见的 90°、10 0°、12 0°埋头紧固件埋头部分与直杆部分相交处的表面裂纹 ,以及直圆杆表面裂纹的应力强度因子进行了计算分析。给出了圆直杆以及 90°、10 0°、12 0°埋头紧固件椭圆形表面裂纹的应力强度因子拟合公式。研究结果表明 ,本文的应力强度因子计算方法和计算结果是有效的。本文的工作可为埋头紧固件的损伤容限分析提供应力强度因子。     

太阳／大气紫外光谱地基观测系统

研制了一套基于Ebert-Fastie型双光栅光谱辐射计的太阳/大气紫外光谱地基观测系统,用于获得太阳直射光谱辐照度和大气前向散射光谱辐亮度数据。详述了整套系统的结构及性能,标定了这台光谱辐射计300~400nm光谱辐照度响应度和光谱辐亮度响应度,并在长春地区(43°50′55″N,125°23′56″E)开展了太阳和大气紫外光谱辐射测量试验,获得了当地太阳和大气紫外光谱辐射数据。     

天空偏振光测量系统的设计

根据一束光的偏振特性可以由斯托克斯矢量来表征的原理,设计搭建了一种天空偏振光测量系统。该系统由计算机、赤道仪、光纤光谱仪和配备了可旋转偏振片的改进式天文望远镜组成,在400~900 nm的光谱分辨率为1.4 nm。赤道仪经过标定后可以实现0~180°方位角以及0~90°高度角的调整,角度分辨率为2.5°。系统的光学全视场为4.5°,使用该系统可以测量全天空的光强辐射度、偏振度以及偏振方位角。由标定结果可知,系统光强测量的重复率在450~500 nm为99%,在500~900 nm为(95±3)%;在400~750 nm偏振度测量误差＜2%,在475 nm处达到1.2%。偏振方位角的测量误差＜2°。     

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。     

A precise method to determine the angular distribution of backscattered light to high angles

We present an approach to measure the angular dependence of the diffusely scattered intensity of a multiple scattering sample in backscattering geometry. Increasing scattering strength give rise to an increased width of the coherent backscattering and sets higher demands on the angular detection range. This is of particular interest in the search for the transition to Anderson localization of light. To cover a range of -60 degrees to +85 degrees from direct back-reflection, we introduced a new parallel intensity recording technique. This allows one-shot measurements, with fast alignment and short measuring time, which prevents the influence of illumination variations. Configurational average is achieved by rotating the sample and singly scattered light is suppressed with the use of circularly polarized light up to 97%. This implies that backscattering enhancements of almost two can be achieved. In combination with a standard setup for measuring small angles up to +/-3 degrees , a full characterization of the coherent backscattering cone can be achieved. With this setup we are able to accurately determine transport mean free paths as low as 235 nm.     

Modulated 3D cross-correlation light scattering: improving turbid sample characterization

Accurate characterization using static light scattering (SLS) and dynamic light scattering (DLS) methods mandates the measurement and analysis of singly scattered light. In turbid samples, the suppression of multiple scattering is therefore required to obtain meaningful results. One powerful technique for achieving this, known as 3D cross-correlation, uses two simultaneous light scattering experiments performed at the same scattering vector on the same sample volume in order to extract only the single scattering information common to both. Here we present a significant improvement to this method in which the two scattering experiments are temporally separated by modulating the incident laser beams and gating the detector outputs at frequencies exceeding the timescale of the system dynamics. This robust modulation scheme eliminates cross-talk between the two beam-detector pairs and leads to a fourfold improvement in the cross-correlation intercept. We measure the dynamic and angular-dependent scattering intensity of turbid colloidal suspensions and exploit the improved signal quality of the modulated 3D cross-correlation DLS and SLS techniques.     

Methods for drift stabilization and photomultiplier linearization for photometric ellipsometers and polarimeters

We describe simple modifications to photometric polarimeter and ellipsometer systems that greatly reduce nonlinearity, component drift, and digital noise effects. A photomultiplier feedback circuit is described and analyzed that varies the effective system linearity by means of a single control. Linearity to 5 x 10(-4) over more than three orders of magnitude of incident light intensity is obtained. Effective double-beam stability to 5 x 10(-5) is achieved by blocking the source intensity over part of an extended measurement cycle. These refinements permit photometric instruments to approach accuracy capabilities compatible with their precision capabilities, and also allow measurements to be made in the presence of ambient scattered light, at high sample temperatures, or using solid-state detectors for which the zero reference is not well defined. As an example, we give the dielectric function of Ge measured from 1.5 to 5.8 eV at a sample temperature of 800 degrees C.     

Correlation method for processing speckle patterns of dynamic light scattering by small particles based on spatial averaging of data

A correlation method for processing dynamic light scattering patterns resulting from laser radiation propagation through solutions and suspensions is proposed which is based on spatial averaging of measurement data on the correlation functions of the intensity of light scattered by small particles.     

在线间歇式浊度仪的研究

根据浊度测量理论推导出液体浊度的散射光测量公式,选用波长>800nm的红外发光管和硅光电池作为光电变换元件,并采用间歇式静态测量方法设计了分析流程,消除了色度和气泡对测量的影响。     

基于AT89C51单片机的烟尘浊度测量系统

由于光透过烟尘后吸收和散射的原因,光强会发生衰减,该文通过比较入射光强I0和透射光强I1的衰减来确定烟尘的浊度C和吸光度E.系统以AT89C51单片机为核心,实现了浊度和吸光度数据的存储、显示和超标报警等功能,为了适应连续精确测量,系统中还设置了定时除尘装置。该系统可用于食品加工、火电厂、煤矿等环境的在线连续监测。     

Experimental statistics of near-field intensity distributions at nanostructured surfaces

Scanning near‐field optical microscopy is a technique in which the resolution is primarily determined by the size of a probe and not by the wavelength of illumination as in classical (far‐field) microscopy. However, the relationship between a sample and its near‐field optical image is usually rather complex. Typical factors responsible, at least partially, for such a complexity are the conditions of illumination and detection, sample characteristics (e.g. roughness and dielectric constant) and optical properties of the probe. Theoretical and experimental works conducted to improve our understanding of the relation between the object and the image have been reported ( Greffet & Carminati, 1997 ). Recently, with the help of a photon scanning tunnelling microscope we have carried out an extensive study of the resultant near‐field intensity distributions due to the elastic (in the plane) scattering of surface plasmon polaritons (SPPs) at metal film surfaces. We have also directly observed (in similar experimental conditions) localized dipolar excitations in silver colloid fractals ( Bozhevolnyi et al., 1998 ). In both cases, the studied phenomena are intimately related to the regime of multiple light scattering, in which the interference effects are rather complicated and therefore a proper interpretation of them was far from being trivial. Thus, even though a certain understanding of many features inherent to the subwavelength light interference phenomena was gained ( Bozhevolnyi & Coello, 1998 ; Bozhevolnyi et al., 1998 ; Coello & Bozhevolnyi, 1999 ), it is clear from the outcome of the investigations that more systematic studies in this context are still needed. A different and more powerful approach may be a statistical study of the recorded near‐field intensity distributions. In this work, we report what we believe to be the first results on experimental statistics of near‐field optical images exhibiting localized optical excitations (related to the regime of multiple scattering of light). We investigated optical images obtained with SPPs excited at different light wavelengths and scattered at different film surfaces, and with different polarizations and wavelengths of light scattered by silver colloid fractal structures. We have found significant differences in statistics between near‐field intensity distributions taken at rough and smooth metal film surfaces and fractal structures. Finally, our predictions seem to be in agreement with theoretical studies reported by other authors ( Sanchez‐Gil & Garcia‐Ramos, 1998 ).     

The phonon contribution to high-resolution electron microscope images

The amount of phonon scattering as a function of specimen thickness is determined for a clean silicon sample, free from amorphous surface layers, by measuring the diffuse scattering in energy-filtered convergent-beam diffraction patterns. It is found that for a 25 nm thick sample, only 7.5% of the intensity scattered to less than 18 nm(-1) is phonon scattered. This means that in a typical high-resolution sample most of the diffuse scattering is caused by surface amorphous layers rather than phonon scattering.     

用动态光散射现代谱估计法测量纳米颗粒

为了解决目前动态光散射软件信号分析法采用的自相关和功率谱估计存在分辨率和方差较低,以及能谱泄漏问题,提出了基于现代功率谱估计的动态光散射信号分析法。对该系统所采用的现代功率谱估计算法和测量系统进行了研究。首先,介绍了动态光散射测量法涉及的光子相关光谱理论和散射光谱估计理论。接着,描述了基于现代功率谱估计的动态散射光谱法,特别是其中阶数p的计算方法。然后,介绍了测量系统,包括硬件部分的光学系统和信号采集处理系统,软件部分的系统开发流程。最后,对粒径分别为30、50、100nm的乳胶球标准颗粒溶液(透光率为96%)进行了实验。实验结果表明:现代谱估计分析法的测量均值误差和重复性误差的平均值分别为1.88%和1.62%,满足国标要求的均值误差和重复性误差2%。