Influence of limited-view scanning on depth imaging of photoacoustic tomography

We study the influence of limited-view scanning on the depth imaging of photoacoustic tomography. The situation, in which absorbers are located at different depths with respect to the limited-view scanning trajectory, is called depth imaging and is investigated in this paper. The results show that limited-view scanning causes the reconstructed intensity of deep absorbers to be weaker than that of shallow ones and that deep absorbers will be invisible if the scanning range is too small. The concept of effective scanning angle is proposed to analyse that phenomenon. We find that an effective scanning angle can well predict the relationship between scanning angle and the intensity ratio of absorbers. In addition, limited-view scanning is employed to improve image quality.     

激光雷达扫描方式

为实现激光束对空域的有效扫描和探测,研究了栅形扫描、李萨茹形扫描、螺旋形扫描和六边形扫描四种常见的激光雷达扫描方式,推导了相应的扫描方程,讨论了参数的物理意义及调整方法;重点研究了栅形扫描和六边形扫描方式下光斑的分布情况,通过仿真分析了两种扫描方式下光束的漏扫率和重叠率,结果表明,在相同扫描条件下六边形扫描方式的漏扫区域最少。展示了基于上述研究内容的扫描控制系统实物图及扫描图案。分析总结了四种扫描方式的特点,给出了每种扫描方式的适用情况及使用建议。     

DG型电子加速器自校正扫描系统的研制

为了提高DG型电子加速器束流扫描均匀度、解决束流中心偏移、提升束流引出效率,开发了一种既可实现X,Y两相互垂直方向均匀扫描又可以实现束流中心自动对中调节的扫描系统。介绍了扫描磁铁及其电源参数的选取依据,阐述了将扫描磁铁和束流校正线圈进行整体式设计的扫描系统扫描电流成形方式及自动对中电路信号调制过程,包括为提高加速器运行安全性而设计的连锁保护信号。产业化现场使用事实已证明,该系统设计完全达到了设计要求,具有优良的扫描均匀度和长时间工作稳定可靠性。     

光学传递函数测量仪刀口和狭缝两种扫描方法比较分析

GC 2 11光学传递函数分析仪是北京理工大学光电工程系自行研制的一台能对折轴、潜望等复杂光学系统进行测量的大型精密测量仪。其测量采用了刀口扫描和狭缝扫描两种方式。但实际应用时 ,用刀口扫描方式得到的光学传递函数值总是小于理论值。通过分析计算 ,得出在相同条件下 ,刀口扫描法比狭缝扫描法抗干扰能力差的结论 ,弄清了长期以来刀口扫描测试数值偏小的问题。     

Compact optical delay line for long-range scanning

We proposed and demonstrated an optical delay line composed of all reflective components for long-range scanning without walk-off problem. The optical delay line consists of a retro-reflector, an inclined reflection mirror and a scanning mirror. The size of the optical delay line is within 2 cm × 2 cm and the scanning range can reach 2.9 mm when the beam is incident at the pivot of the scanning mirror and the vibration angle of the scanning mirror is 9.6°. The scanning range can be further increased when the pivot of the scanning mirror is laterally deviated from the incident beam. The optical delay line possesses the advantages that it is compact, easy to fabricate and can perform rapid scanning in large scanning range without walk-off problem. The optical delay line was demonstrated with a low-coherence reflectometer where the scanning rate was 400 Hz. A higher scanning rate can be achieved when a scanning component with higher scanning rate is applied.     

双光子和多光子共焦显微镜的成像理论

对双光子和多光子共焦扫描显微镜的成像理论作了系统的理论分析,导出了双光子和多光子共焦显微镜成像系统的三维点扩散函数和三维光学传递函数,研究结果表明：双光子共焦显微镜比单光子共焦显微镜具有更高的横向分辨率和纵向分辨率,而多光子共焦扫描显微镜又比双光子共焦扫描显微镜具有更高的空间分辨率. 关键词：     

Two-axis-scanning laser Doppler vibrometer for precision engineering

Laser Doppler vibrometer (LVD) has been the most favorite instrument for precision dynamics measurement due to its non-contact, high accuracy and high resolution. However, LDV can only give the dynamic data of a particular location on the entire feature. In order to get the whole field data, a laser beam-scanning mechanism has to be implemented. Currently, motor-driven scanning mirror is used to move the measurement probe from one point to another. The mechanical vibrations of the scanning mirror will reduce the measurement accuracy. This paper introduces a novel scanning LDV optical system embodied in an acousto-optic deflector scanning mechanism. It can improve the measurement accuracy since there is no mechanical motion involved. One main advantage of this system is that it generates a laser scanning beam in parallel that is different from the beam scanning in the conventional scanning laser Doppler vibrometer (SLDV). The new system has a board scanning range. The measurement target size ranges from few tens of millimeters down to 10 μm. We have demonstrated the capability of the novel system on scanning measurements of features as big as ultra-precision cutting tool to features as tiny as AFM cantilever. We believe that the novel SLDV will find profound potential applications in the precision engineering field.     

电光双折射扫描滤波法提高啁啾脉冲对比度

提出了一种通过扫描滤波来提高啁啾脉冲对比度的方法,并分析了该方法的原理。与传统的非线性滤波技术不同,扫描滤波方法消除预脉冲时,选通原理是基于光的频率而不是强度。以电光双折射扫描滤波器为例,说明了扫描滤波法的具体应用。通过数值模拟及实验研究,发现电光双折射扫描滤波法可以有效地消除主脉冲以前几百ps的预脉冲,并且主脉冲同时还能保证较高的透过率。     

磁流变加工的连续相位板波前及光强特性

对采用磁流变抛光(MRF)工艺加工的大口径连续相位板(CPP)的波前及其光强控制特性进行了分析,对由不同的加工参数(走刀间距和走刀偏置)所加工的三组CPP进行了比较,并分析了MRF加工所引入的中频误差对CPP波前和光强特性的影响。结果表明,走刀间距为2mm、对应走刀偏置范围为0.1~0.3mm时所加工CPP的波前及其光强控制能力较差,远场有一定程度的旁瓣产生;走刀间距为2mm、偏置范围为0.4~0.5mm时所加工CPP和走刀间距为1mm、偏置范围为0.1~0.3mm时所加工CPP相比较,迭代加工效率提高,CPP波前中频误差得到一定的改善。进一步分析表明MRF所引入的中频误差对CPP波前梯度及旁瓣影响较大。     

基于数字微镜的快速轴向扫描系统

为解决双光子荧光显微成像系统轴向扫描问题,提出一种基于数字微镜(DMD)的快速轴向扫描系统。该系统采用DMD选择光路,不同光路放置不同焦距的透镜组对光束发散角产生不同的改变,经物镜聚焦后得到不同深度的轴上扫描点。对该系统的轴向扫描距离、扫描点位置及衍射效率进行了理论计算仿真,结果表明:扫描系统采用4个模块以及5个模块时其轴向扫描距离均可达到1 mm,4模块系统中透镜的焦距为297.3 mm,5模块系统中透镜焦距为361.47 mm。轴向扫描点除边缘点外线性分布, 轴向扫描频率达到几十kHz,满足脑神经成像的要求。     

Speckle analysis in laser scanning display system

The theory of speckle formation in laser scanning display system is established based on the averaging effect of eye response as laser beam scanning through an eye resolution spot. It is analyzed that speckle reduction can be obtained by averaging states of speckle during scanning. The theoretical results show that a smaller correlation length of screen surface and the narrowing of laser beam in scanning direction can reduce speckle contrast for this system.     

Experiments and analyses of a new type optical system for computed radiography

A new high-performance laser scanning system is designed. In this system, a scanning arm consisting of a pentagonal prism and a scanning object lens is used to replace the traditional Fθ lens, and a circular imaging plate transmission mechanism is specially designed in order to meet the requirement of the scanning arm. At the same time, the stimulation fluorescence can be obtained by the scanning arm. Some main factors that influence the spatial resolution and the performance of the laser scanner system are analyzed, and the analysis results are presented, which is helpful for further optimization design of the system. Experimental results indicate that the images obtained by the system have good visual effects and can meet the requirements of industrial inspection.     

高精度基准平面建立方法分析

基准平面的确立,是进行表面参数评定的基础;建立理想的基准平面,在几何量形位公差检测及相关工程测量方面具有重要作用.为了建立高精度的激光扫描基准平面,对扫描平面形成过程中光束的传播进行了详细分析;根据光学矢量反射定律,推导出了扫描误差的理论公式;在此基础上揭示了误差补偿的基本原理,导出了用于补偿扫描机构产生的扫描误差的理论公式;提出了据此准则进行设计的扫描机构的模型.分析表明,用激光及其扫描装置建立光学基准面时,扫描误差是不可避免的,这种误差不加补偿,则最终将引入基准光学平面影响基准精度,进而降低参数的评定精度;借助于所推导的误差补偿公式,是可以补偿这种误差的,这对于建立高精度的扫描基准平面具有理论指导意义.     

A scanning distortion correction method based on Ⅹ–Y galvanometer Lidar system

Aiming at the problem of scanning distortion in X-Y galvanometer light detecting and ranging(Lidar) scanning system,we propose a method of image scanning distortion correction with controllable driving voltage compensation.Firstly,the geometrical optics vectors model is established to explain the principle of pincushion distortion in the galvanometer scanning system,and the simulation result of scanning trajectory is consistent with experiments.The linear relationship between the driving voltage and the scanning angle of the galvanometer is verified.Secondly,the relationship between the deflection angle of the galvanometer and the scanning trajectory and the driving voltage is deduced respectively,and an image scanning correction algorithm with controllable driving voltage compensation is obtained.The simulation experiment results of the proposed method show that the root-mean-square error(RMSE) and the corresponding curve between the scan value and the actual value at different distances,have a good correction effect for the pincushion distortion.Finally,the X-Y galvanometer scanning Lidar system is established to obtain undistorted two-dimensional scanned image and it can be applied to the three-dimensional Lidar scanning system in the actual experiments,which further demonstrates the feasibility and practicability of our method.     

融合单目视觉的激光扫描投影系统自标定方法

为解决现有激光扫描投影系统中需要手动标定的问题,提出了融合单目视觉的激光扫描投影系统自标定方法.首先建立了融合单目视觉技术的激光扫描投影系统模型,给出了融合单目视觉的激光扫描投影系统自标定方法;其次建立了单目相机与激光扫描投影系统、被投影物体之间的数学模型;最后运用Matlab软件进行模拟仿真,证明融合单目视觉的激光扫...     

极坐标系统下进行直角坐标扫描的离子束抛光

在离子束抛光设备研制过程中,离子源扫描运动方式的选择是很关键的,一般分为直角坐标方式扫描和极坐标方式扫描两种。根据两种扫描方式的特点,在极坐标系统下进行直角坐标扫描方式加工。该种方法采用直角坐标扫描方式下的驻留时间计算,算法相对简单。该种方法在极坐标系统下进行加工,同等情况下可加工圆形镜面的口径比直角坐标系统下更大些;而且离子源的可移动区域是一条直线,其余地方可以摆放其他设备,空间利用率较高。对这种新思路进行仿真分析,证实了其具有可行性。     

电介质陷阱能量分布的光刺激放电法实验研究

利用光刺激放电方法研究了线性低密度聚乙烯(LLDPE)中的陷阱能级分布,分别介绍了连续扫描与分段扫描这两种扫描方式并对它们进行了对比.指出在通常使用的连续扫描过程中,光刺激脱阱的不彻底给实验数据带来了一定的误差,着重讲述了分段扫描的理论基础以及实验过程.实验结果表明:单一波长辐照下的光刺激衰减电流的对数与时间成线性关系,它和分段扫描方法中的理论分析完全符合,同时也验证了在本实验中忽略载流子的重俘获过程是合理的;LLDPE中的俘获电荷位于4.14—6.22eV的陷阱能带内,但它们主要集中在陷阱能级为4.78     

光子扫描隧道显微镜球形样品二维近场强度分析

采用时域有限差分方法计算全内反射和光子扫描隧道显微镜系统。光子扫描隧道显微镜的基本工作原理是隐失波的产生和探测，当入射光在两种介质的分界面上发生全内反射，并在界面处产生非辐射的电磁波——隐失波时，采取对两界面入射光进行分别设置的方法即“三波法”设置入射激励元。分别计算一个球和两个球形样品的近场分布，并计算散射小球为探针，一个球为样品的扫描图像。结果表明：采用二维时域有限差分方法计算能较直观地显示样品表面的近场分布。表明时域有限差分方法在光子扫描隧道显微镜理论研究中具有很大潜力。     

Scanning moiré and phase shifting with time delay and integration imaging

Scanning moiré is generated by undersampling of a phase-modulated grating pattern. In projection profilometry the scanning moiré pattern represents equal height and depth contours on a test object. By use of time delay and integration (TDI) imaging, it is possible to generate an on-line scanning moiré pattern from the complete periphery of a rotating cylindrical object. For automated phase and profile unwrapping from scanning moiré fringes, phase-shifting interferometry techniques are most desirable. However, lack of spatial information in the undersampled scanning moiré fringes introduces serious errors in phase unwrapping. We report a method that uses oversupply of data to balance the effect of undersampling. This oversupply is achieved with a TDI feature that permits programmable image magnification in the scanning direction.     

Study on fast linear scanning for a new laser scanner

In the field of lidar system design, there is a need for laser scanners that offer fast linear scanning, are small size and have small a rotational inertia moment. Currently, laser scanners do not meet the above needs. A new laser scanner based on two amplified piezoelectric actuators is designed in this paper. The laser scanner has small size, high mechanical resonance frequencies and a small rotational inertia moment. The size of the mirror is 20 mm×15 mm. To achieve fast linear scanning performance, an open-loop controller is designed to compensate the hysteresis behavior and to restrain oscillations that are caused by the mechanical resonances of the scanner's mechanical structure. By comparing measured scanning waveforms, nonlinearities and scan line images between the uncontrolled and controlled scanner, it was found that the scanning linearity of linear scanning was improved The open-loop controlled laser scanner realizes linear scanning at 250 Hz with optical scan angle of ±12 mrad.