共查询到19条相似文献,搜索用时 46 毫秒
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强冲击载荷下自由表面的粒子喷射现象还没有被清楚认识,很难从理论上给以准确的计算模型,因而从实验测定材料在冲击载荷下自由面面喷射物质的分布和粒子尺寸大小就显得非常重要。测量微粒场的脉冲激光同轴全息技术,具有在纳秒或更在短时间内“固化”运动微粒场、测量精度高、景深长、光路简单和获得的信息量大等优点。这些优势使得脉冲激光同轴全息技术成为研究微喷射场的重要测试手段之一。 相似文献
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由于激光全息技术进行物理测试时具有图像直观、信息量大、非接触测量、抗电磁干扰等优点,而受到人们的广泛关注。采用同轴Fraunhofer全息技术记录微射流粒子场的实验装置由激光器、爆轰实验装置、4F传像系统、记录系统、时问同步系统等组成。爆轰实验装置为一可抽真空的爆炸容器,其目的是为了产生一个微射流粒子场,实验研究中在铜飞片上打一些小坑,当冲击波到达时小坑中将能产生微射流;脉冲宽度为10ns的记录用激光器可以将直径为几十微米、运动速度为每秒几千米的微射流粒子场瞬间“冻结”,从而获得清晰的全息图像;通过调节DG535精密数字延迟脉冲发生器输出信号的延迟时间,控制脉冲激光器出光和爆轰实验装置爆炸的时间,从而达到产生运动粒子场和脉冲激光束到达时间的同步。通过同步调节延迟时间,可以获取同一空间不同时刻的粒子场信息。对拍摄的全息图经过线性处理后在连续YAG陪频激光器下再现,将再现获取的信息利用CCD相机储存在计算机上,对图片进行处理可以获取运动粒子场的分布、粒子的大小、粒子的质量等信息。 相似文献
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在高压加载下材料表面会产生微物质喷射,传统全息技术已应用在微物质喷射的测量中,获得包含粒子形状和位置信息的再现图像。数字全息技术作为传统全息技术的一种替代手段,直接采用CCD相机接收微喷射粒子的全息图像,再用数字方法重建粒子场,由于其避免了传统全息中干板的湿处理,并且不需要物理再现过程,具有实验过程简单方便、噪声小、实验结果直观、实时处理等优点。文中讨论了采用同轴数字全息技术测量微喷射粒子的实验情况,获得了铝飞片在爆轰加载下的微喷射粒子的数字全息图像和再现图像,给出了粒子的尺寸分布和微喷射粒子的速度。 相似文献
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在数字全息干涉原理的基础上设计了用于泊松比测量的数字激光全息实验装置,利用该装置经过样品加载、全息图记录、全息图数值重建和泊松比计算步骤即可以获得材料的泊松比,实现非接触和实时测量.碳/碳复合材料的泊松比测量结果表明实验准确,重复性较好. 相似文献
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采用数值方法模拟了同轴全息术测量粒子场的过程,对两种不同的数值算法_直接傅里叶变换算法和卷积算法,进行了分析和比较,结果表明卷积算法符合实际要求。分析了记录图像的空间频谱及其对图像采样频率的要求,得出了在记录波长、采样间隔等条件一定的情况下的最小记录距离。对于一幅512×512像素的数字图像,若像元尺寸为6.7 μm,所用光波长为532 nm,则最小记录距离为43.2 mm。在此基础上对实验记录的振幅和相位型静态粒子的数字全息图,均得到了满意的数值再现像。 相似文献
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The diffraction of an ultrashort pulsed laser beam by an opaque particle is studied. The case of a pulse with a Gaussian spectrum is investigated analytically by using the steepest descent method. This analytical solution allows us to calculate the intensity distribution of the diffraction field. This result enables to determine the optimal fractional orders Fourier transform to reconstruct digital in-line particle hologram. 相似文献
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Vijay Raj Singh Jianmin Miao Zhihong Wang Gopalkrishna Hegde Anand Asundi 《Optics Communications》2007,280(2):285-290
In this paper dynamic characterization of a MEMS diaphragm is investigated using lens-less time averaged in-line digital holography. The analysis and capability of the numerically reconstructed amplitude and phase information from in-line time averaged holograms as applied to MEMS vibration are presented. Particularly the effect of mean static state on the phase in time averaged digital holography is explored. A novel double exposure method is also demonstrated using a diverging object wave suitable for dynamic characterization of small size objects. A phase jump in the static deformation fringes in the vibrating regions is observed and described and can be used for precise analysis of vibration mode shape under simultaneous presence of mean static deformation. A simple and robust tool for dynamic optical metrology of MEMS devices and micro-objects using time averaged in-line digital holography is thus proposed. 相似文献
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In-line particle holography is a well-known method used for visualization and measurement of small objects such as sizes, 3-D positions and velocities. However, this method suffers from a major drawback that is conventional analysis of its reconstructed images is very tedious and time consuming. In this paper, we review recent progress in holographic particle tracking and sizing by using wavelet transform. Recent experimental results of spherical object measurement are noted. 相似文献
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Longchao Yao Chenyue Wu Yingchun Wu Linghong Chen Jun Chen Xuecheng Wu Kefa Cen 《Proceedings of the Combustion Institute》2019,37(3):2911-2918
Devolatilization is an important process in pulverized coal combustion because it affects the ignition, volatile combustion, and subsequent char burning and ash formation. In this study, high-speed digital in-line holography is employed to visualize and quantify the particle and volatile evolution during pulverized coal combustion. China Shanxi bituminous coal particles sieved in the range of 105–154 µm are entrained into a flat flame burner through a central tube for the study. Time-resolved observations show the volatile ejection, accumulation, and detachment in the early stage of coal combustion. Three-dimensional imaging and automatic particle extraction algorithm allow for the size and velocity statistics of the particle and stringy volatile tail. The results demonstrate the smaller particle generation and coal particle swelling in the devolatilization. It is found that the coal particles and volatiles accelerate due to the thermal buoyancy and the volatiles move faster than the coal particles. On average, smaller particles move faster than the larger ones while some can move much slower possibly because of the fragmentation. 相似文献
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We propose an approach based on axial translation of a charge-coupled device (CCD) and gradient operator method for numerical reconstruction in in-line digital holography. The object wave in the hologram (or CCD) plane is determined using one position translation of CCD, and a phase-shifting device can be fully avoided. Gradient operator method is further applied to detect the focal plane of an object, and the object wave is reconstructed by an angular spectrum algorithm with the detected focal distance. The feasibility and effectiveness of the proposed method are demonstrated by numerical simulations. 相似文献
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Potential of digital holography in particle measurement 总被引:14,自引:0,他引:14
This paper describes the potential power of digital holography in particle measurement and its expected development in the near future. In digital holography, image reconstruction is carried out numerically on a computer using observed hologram patterns and some quantitative information can be derived from the reconstructed images. In this paper, the basic concept and procedure of digital in-line holography are shown mainly for particle depth measurement and the performance test results obtained in numerical simulations and experiments are demonstrated to examine the potential of the present method. 相似文献
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A novel digital method for tracking position of objects from in-line holograms by using single wavelet coefficient is proposed. In the proposed method, a wavelet transform is used to analyze the holograms. An axial position of the object being studied is determined by using a real value of a resultant wavelet coefficient appears at a center position of interference fringes. A feasibility of this method is experimentally verified by analyzing holograms of an optical fiber. 相似文献