跟踪测量电视全自动调光系统

介绍一种实际应用的跟踪测量电视的调光系统。它采用视频信号控制带有电子快门的ＣＣＤ摄像机的积分时间以平面电机自动光圈,实现范围全自动调光、简要叙述了光系统的组成和工作原理。     

Q开关Nd:YAG激光治疗机关键参数计量检测装置研制

针对脉冲激光治疗机关键参数溯源难的问题,基于LabVIEW和USB总线技术设计并研制了Q开关Nd:YAG激光治疗机关键参数计量检测装置。实现了对治疗激光和瞄准激光关键参数的计量检测及自动生成检测报告等功能,其主要功能模块有:脉宽、能量、重复频率、光斑尺寸和束散角、波长以及瞄准激光功率测量模块。在光斑测量模块中,在传统“刀口法”中引入反馈机制并实现了全自动测量,可自适应不同脉冲频率的激光。研究了其溯源方法,光斑尺寸测量不确定度达到了3.2%。对研制的装置其它参数也做了不确定度分析,包括激光波长、脉宽、能量、重复频率和瞄准激光功率,其不确定度分别为0.6 nm、4.0%、3.2%、0.12%和3.4%。     

一种基于亮度阈值的激光光斑中心定位算法

激光光斑图像的光斑中心定位是激光位移检测中的关键技术之一.为提高桥梁挠度测量系统的实时性能,本文针对测量中激光光斑图像的特点,提出了一种确定光斑中心位置的方法.利用激光图像中光斑区域与其它区域亮度差别较大的特点,确定亮度阈值并将光斑图像进行二值化处理,得到一幅仅有激光光斑的图像,根据圆上平行弦的中点连线通过圆心的原理,通过求弦的中点确定圆心.本方法原理简单,计算量小,计算速度快,能够满足测量系统的实时性要求,已在测量实验中取得了较好的效果.     

利用二次成像法实现外场激光光斑测量

本文介绍了二次成象法测量光斑的原理,对外场测量光斑的方法.试验结果证明二次成象法巧妙地结合了两种成像器件的优点,既提高了测量系统对激光的响应灵敏度,又可利用异步CCD有效抑制太阳背景,增加系统的作用距离.该方法是解决外场激光光斑测量的一种有效手段.     

激光测振仪用于微梁和AFM探针振动测量

激光光纤测振仪将直径小于200μm的激光光斑会聚于Si微悬臂梁和AFM探针上，分别由静电场和PZT进行激振，实现了激光微结构振动特性非接触测量，并给出了测量结果。     

摄像机与照相机快门的异同

摄像机与照相机快门的异同金林摄像机的快门和照相机的快门，从原理上看，功能是一样的，即控制通光时间，与光圈共同决定曝光量，用与光圈的互易律控制景深，用高速快门拍摄运动物体等。但是，由于摄像是连续拍摄，照相每次拍摄一张照片；电视画面是活动的，照片是静止的...     

一种新型的激光远场光斑直接测量技术

激光远场光斑测量对描述激光束的远场性能,评价激光器以及系统的实际工作性能具有重要意义。通过比较激光光斑远场直接测量与间接测量的优缺点,提出使用单片机控制的探测器阵列进行远场光斑直接测量。分析了数据传输、光电转换单元等关键技术,给出了主要程序的框图。该系统采用由上位计算机、主单片机和下位单片机构成的分布式结构,能够测量激光光斑大小、形状、总能量、能量分布等参数,可适用于单脉冲至几百赫兹、中高能量以下的激光器,并且测量精度高。     

热扩散率测量中激光非均匀加热的研究

激光闪光法是测量材料热扩散率的一种瞬态测量方法,是测量速度最快的方法之一,也是目前最受欢迎的方法之一.通过对闪光法测量装置中激光器输出光斑的实时探测,发现大能量下光斑分布的均匀程度明显优于小能量下的分布情况.通过设计实验,验证了光斑的这种分布情况以及激光非均匀加热对热扩散率测量结果确有一定影响.为此,特设计一套光学装置...     

远距离激光光斑定位中的光晕抖动抑制算法

在机械工程等领域,大型桁架等空间结构的空间定位需求十分普遍。激光光斑定位通过激光光源对反射标志补光,工业相机获取反射回来的激光光斑。算法采用Canny算子获取光斑边缘,最小二乘圆拟合得到拟合光斑圆心位置实现定位。在远距离光斑定位中,激光光斑边缘容易出现光晕抖动的现象。为抑制光晕抖动误差,提高系统测量精度,该文提出基于时序滤波和二次拟合的两种光晕抑制抖动的算法,分别基于对时序测量值进行平滑滤波的思想和剔除误差较大的噪声点后再次拟合的思想来消除光晕抖动对系统测量的影响,最后结合测量距离12.36 m的反射靶标的光斑定位实验进行分析对比,最终二者将重复性误差界上、下限分别优化到±0.22pixel和±0.26pixel,能有效抑制光晕抖动产生的测量重复性误差。     

科学研究方法论

主要讨论在科学研究工作中如何获得创新性成果的方法．全文分为两部份，即理论研究和实验研究。理论研究部分论述物理学中的概念和符号体系、物理定律及其表示形式、物理理论及其判据；实验研究部分强调实验研究在创造性科研中的重要意义、论述实验时实验者的思维活动、介绍作者本人常采用的一个思维方法，以及捕捉创新概念的各种方法。从1954年起，这些方法先后帮助作者在电子发射、真空物理、真空测量、气体激光、激光测量、统计物理、铁轨几何参量在线测量等领域，取得了范围较广泛的创造性成果。     

飞秒激光烧蚀MgAl2O4透明陶瓷的实验研究

实验研究了800nm飞秒激光与MgAl2O4透明陶瓷的相互作用，得到其在单脉冲、多脉冲情况下的损伤阈值和损伤面积，用CCD成像技术和扫描电镜观察了烧蚀点的形貌特征，用显微红外光谱仪测试了烧蚀区域的透过光谱．结果表明；单脉冲烧蚀条件下，烧蚀面积与脉冲能量近似为线性关系，而在多脉冲烧蚀条件下，烧蚀面积随着脉冲数量的增加呈近似波尔兹曼（Boltzmann）增大；当激光功率接近损伤阈值时，烧蚀后的区域在波数为2500-7000cm^-1范围内的红外透过率由82％提高到86％，当激光功率超过损伤阈值后，透过率降低20％左右．     

Femtosecond electron beam generation and measurement for laser synchrotron radiation

One of the S-band twin linacs (18L linac) of Nuclear Engineering Research Laboratory of University of Tokyo is modified in order to produce femtosecond electron single bunch for femtosecond X-ray generation via Thomson backward scattering, namely laser synchrotron radiation. Laser photocathode RF gun and chicane-type magnetic pulse compressor are installed at the S-band linac. 10 ps (FWHM) laser pulse generates 5 MeV, 10 ps (FWHM), 1 nC electron single bunch, which is accelerated up to 20 MeV in the S-band accelerating tube and compressed to 200 fs (FWHM) by the chicane. Design study has been performed by using the code of PARMELA and the installation has been finished. For precise and reliable measurement of the compressed pulse length, the comparison of measurement between the femtosecond streak camera and coherent transition radiation interferometry was carried out. Good agreement between them for 1-10 ps (FWHM) pulses was achieved. A new Michelson interferometer for the 200 fs pulse is now under construction.     

The 41st Physical Society Exhibition 1957

The control unit was built so that any ciné camera could be used to take single fram; exposures of living micro organisms under a microscope. The exposures and the intervals between exposures are variable, the latter being completely independent of the former.

For single frame exposures a Kodak electric release solenoid was used, this operating the release mechanism on the camera. When the solenoid receives a pulse it opens the camera shutter, a second pulse closes it and moves the film on to the next frame. Throughout the filming the microscope stage is illuminated by a strong source of light. To reduce the overheating effect a shutter has been built, which cuts off the beam during the interval between exposures.

The electronic control unit has the advantage of being small and costing only a few pounds to build.     

基于电子快门实现CCD曝光量无级调节技术

为了在景物照度变化条件下保持图像特定目标的亮度基本恒定,提升摄像测控系统的性能,提出了CCD电子快门配合分档光圈实现曝光量无级调节的自适应控制方法。该方法针对光圈换档和电子快门动作在延时性能上的显著差异,将光圈换档对光通量的粗调和电子快门时间的精调两者实时配合,来控制曝光量,算法的实际运用需要通过实验建立光圈换档动力学模型。     

Time-resolved beam-quality characterization of copper-vapor lasers with unstable resonators

Beam quality (BQ) of a 4-cm copper-vapor laser (CVL) with unstable resonators of different magnifications was characterized based on time-resolved far-field measurement. It was found that the BQ improvement after each round trip of the cavity cannot be predicted correctly from resonator theory. With a cavity Fresnel number of ~ 300, the achievable CVL BQ at the later part of the pulse was limited to approximately 4 times diffraction limited (×DL), even with a cavity magnification of 130. A pronounced temporal BQ oscillation, which is synchronized with the temporal pulse modulation, was also observed throughout the entire pulse. Examination of the temporal evolution of the far-field spot with use of a gated camera revealed that the strong presence of amplified spontaneous emission (ASE) in the cavity during the entire laser pulse severely limited the achievable BQ because of consecutive cavity feedback that included this highly divergent ASE. BQ deterioration caused by intense ASE throughout the pulse was reduced when a cavity with a smaller Fresnel number was used.     

Electron bunch compression and acceleration in the laser wakefield

The compression and acceleration of an external electron bunch into the laser wakefield is studied using 3D modeling with the LAPLAC code and compared to analytical predictions. It is shown, for a laser propagating in a plasma channel, that the nonlinear laser pulse dynamics together with the finite laser spot size influence the electron bunch compression and acceleration due to the reduction of the laser pulse group velocity. The transverse bunch dynamics and loading effect determine the final bunch charge and density and restrict the compressed sizes of the trapped and accelerated electron bunch. The dynamics of the electron bunch are illustrated with a set of parameters where the accelerated bunch acquires an energy of the order of 2 GeV, and 1% energy spread with sub-micron sizes.     

A Technique for the Testing of Camera Shutters

A method of testing camera shutters is described and illustrated examples of the application of the method are given. The method is applicable to all types of shutter mechanism and uses standard laboratory equipment. Double extension or a supplementary lens is required for a full test on a focal plane shutter. The method involves photographing a trace on a cathode-ray tube screen.     

Measurement of spatial cross sections of ultrasound pressure fields by optical scanning means

The measurement of spatial cross sections of ultrasound pressure fields is an essential element of exposimetry of ultrasonic medical equipment. An optical technique is presented that allows the two-dimensional (2-D) determination of ultrasound pressure using an optical multilayer hydrophone in which a laser beam with suitable wavelength is partially reflected from a dielectric optical multilayer system. By detecting the change in reflectivity of the multilayer coating induced by the incident ultrasound, the pressure time waveform can be determined. A 2-D data acquisition covering an area of at least 15 mm x 5 mm was realized by two complementary approaches. A serial detection scheme was set up by scanning the sensing point across the area of interest by a micromechanically engineered scanning mirror and acquiring pressure time waveforms sequentially and pointwise. This allows the measurement of repeating ultrasonic waveforms with a spatial resolution of better than 70 microm and a minimal detectable pressure of 50 kPa (bandwidth: 50 MHz) in a few seconds. In an alternative approach exploiting the parallel processing capabilities of a charge-coupled devices (CCD) camera chip, the probe was strobe-illuminated by a large-diameter collimated beam of a pulsed laser diode. The 2-D pressure distribution at a particular moment was derived from captured reflectivity distributions with a spatial resolution of 75 microm. By successive delaying of the laser pulse with respect to the ultrasound pulse, the complete 2-D pulse waveform was acquired with high spatial resolution. Measurement results on ultrasound fields from plane and focusing transducers are presented and compared to simulation results. Individual advantages and drawbacks of both approaches are discussed. A combined setup merging both detection schemes into a single device was developed and represents a milestone on the way toward constructing an optical ultrasound measuring camera.