利用单幅同轴菲涅耳数字全息图重构物光波面

在数字全息研究中,为了充分利用CCD器件有限的卒间带宽积,常采用同轴全息记录.然而用同轴全息图再现时,再现物光波和共轭物光波是混在一起无法分开的.有效消除同轴全息图再现光波场中的共轭像是数字全息应用中的一项关键技术.基于菲涅耳衍射运算和逆运算,提出一种用同轴数字全息图重构物光波面的迭代算法.该方法利用同轴全息图再现时,再现物光波和共轭物光波衍射特性的不同来剔除共轭物光波成分,从而将再现物光波成分有效分离出,实现单幅同轴全息图的物光波面数值重构.计算机模拟实验证明了该方法简单易行.     

球面波全息微粒测量系统性能的研究

在测量微粒场的全息技术中,通常采用平面波系统进行记录和再现.由于全息图衍射效率低,微粒全息像误差大,限制了使用范围.本文导出了用球面波系统记录微粒全息图和再现微粒像的理论公式.并对两种系统全息记录的调制度、全息图衍射效率、再现像误差作出比较.分析和实验结果表明,在这些方面球面波系统较之平面波系统更为优越.     

合成孔径同轴数字全息图的相位恢复再现（英文）

针对有缝拼接合成孔径同轴数字全息图的再现问题,通过对接缝处预先进行灰度均值填充,利用基于角谱理论的Gerchberg-Saxton(GS)加权改进相位恢复算法恢复相位,获得全息图记录面上的完整复振幅信息.仿真模拟了该方法对粒子场的检测,获得的再现像与模拟粒子靶的相关系数较传统方法得到的结果提高1倍以上,并可以有效抑制接缝处信息丢失对合成孔径同轴数字全息图再现像的影响,实现有缝拼接合成孔径同轴数字全息图的高质量再现.     

粒子场数字全息诊断中的再现算法研究

 粒子场的数字全息诊断中,良好的再现算法能够在较短的时间内给出高质量的再现像。利用标准粒子板模拟单层面的粒子场,使用大面阵CCD实现同轴数字全息记录,得到了大尺寸的数字全息图。针对4种数字全息再现算法,本文从再现图像的质量、再现全息图的大小和计算速度3个主要方面进行了比较研究,结果表明角谱算法(FFT-AS)具有再现图像背景均匀,再现结果中无物理图像压缩,可以再现大尺寸的全息图且具有较快计算速度的优点,适合于粒子场同轴数字全息图的再现计算。     

乙醇喷雾场粒子尺寸和速度的数字全息测量

利用连续波激光器和高速CCD,采用数字同轴全息系统,记录了乙醇喷雾粒子场全息图.对粒子场再现像进行聚焦像合成,自适应滤波、二值化、Roberts边缘提取,Hough变换和亚像素精度计算,得到粒子的直径和位置信息.利用两次曝光记录的两个序列全息图得到粒子位移,进而求得粒子的运动速度,给出了实验结果.研究结果表明,该实验系统可用于内燃机喷雾场测量,且具有光路系统简单、成本低等特点.     

动态微粒场分析的同轴全息技术

本文描述了采用同轴远场全息术测量柴油机动态油雾场的实验方法和原理,并讨论了横向放大率、全息图的衍射效率及离焦象几个方面的问题。     

动态微粒场诊断用全息光路的设计与分析

本文分析了动态微粒场测试的特点,设计了一种适合于动态微粒场用脉冲激光全息诊断的全息光路,并从理论上进行了分析。使用这种全息光路记录的微粒场全息图,当用记录参考光,而不是它的共轭光照明再现时,就能获得微粒的实象,因而,使得参考光类型的选择更加灵活。同时,由于光路设计上还考虑了参物光之间的空间相干性的匹配,故降低了对激光器横模的要求。     

粒子场相移全息术

本文利用相移全息术记录的双曝光粒子场全息图,以改进再现图像的SNR、分辨率和对比度。并发展了这种技术的理论,讨论了相移的引入方法,给出了实验结果,与通常的同轴和离轴双曝光结果进行了比较。     

用脉冲激光同轴全息技术测量微射流

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。     

基于双色光照明的单曝光同轴数字全息技术

提出了一种基于双色光照明的单曝光同轴数字全息技术。在红绿蓝三色中,任选两种波长的光来照射物体,采用彩色CCD记录双色同轴全息图,然后经过三基色分离数字处理,可得到两幅不同波长的同轴全息图。用角谱衍射理论对该技术进行了分析,表明在降低物参光振幅比的条件下,通过对同轴数字全息图求自然对数,可近似得到衍射物光及其共轭之和,其误差与物参光振幅比有关。取两幅不同波长的同轴数字全息图,经自然对数处理后,用传递函数可以很好地重构出物体图像,给出了具体的数字处理算法。用仿真实验,模拟了该技术的全息记录和处理过程,得到重构图像的峰值信噪比(PSNR)为14.2 dB。结果表明该方法可以去除孪生衍射像干扰,可以实现清晰的单曝光同轴全息成像。最后,分析了再现像中噪声产生的原因。该技术可用于基于同轴全息的实时成像与动态测量。     

非线性介质对粒子场同轴全息成像的影响

 通过理论分析和实验验证,研究了非线性折射率介质对粒子场同轴全息成像的影响。利用粒子场同轴夫琅和费全息记录和光束在非线性介质中传输的波动方程,得出了光波的复振幅和强度分布。数值模拟了介质在线性和非线性时全息记录的情况,并进行了实验验证。结果表明：光波经非线性介质传输后,全息干板记录到粒子场的再现图像,这为高功率激光应用于全息照相提供参考,原因是高功率脉冲激光聚焦易击穿介质产生非线性传输。     

Characterization of diffraction patterns directly from in-line holograms using the Gabor transform

The Gabor transform is used for object characterization directly from in-line holograms, three-dimensional locations of the object can be determined from the Gabor transform spectrum of its in-line hologram. The relation between the Gabor angle and the location of the object is established. Simulation and experiment results are also presented to show the validity of this method. This method can be applied in particle field analysis.     

Digital particle holographic system for measurements of spray field characteristics

A digital particle holographic system for measurements of spray fields is presented. A double exposure hologram recording system with a synchronization system for time control is established, resulting in digital holograms that can be quickly recorded. To process recorded holograms, the correlation coefficient method is used for focal plane determination of particles. To remove noise and improve the quality of holograms and reconstructed images, a Wiener filter is adopted. The two-threshold and image segmentation methods are used for binary image transformation. For particle pairing, the match probability method is adopted. The proposed system is applied to a spray field, and three-dimensional velocities and sizes of spray droplets are measured. Measurement results from the digital holographic system are compared to those made by laser instruments, which prove the feasibility of the proposed in-line digital particle holographic system as a good measurement tool for spray droplets.     

Particle digital in-line holography with spherical wave recording

In this paper, we propose a method of digital in-line holography of particle. A diverging spherical beam is used for illumination in recording hologram, the complex amplitude distribution generated by particle field at a single plane located in the Fresnel diffraction region is recorded by CCD, and a plane beam for reconstructing hologram, then, the magnified image can be obtained by numerical reconstruction in computer. This procedure can be interpreted by Fourier optical theory and the theoretical analysis have been done in detail, the experimental results, the air freshener being subject, are also given.     

Digital in-line holography with a sub-picosecond laser beam

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.     

Phase signature for particle detection with digital in-line holography

The spatial phase resulting from the digital reconstruction of an in-line hologram of a particle field is shown to yield a unique pattern that can be used for particle detection. This phase signature is present only when viewed along with the reference light. The existence of the phase pattern is verified computationally and confirmed in laboratory experiments with holograms of calibrated glass spheres. The phase signature provides an alternative to the widely used intensity method for particle detection.     

用脉冲激光同轴全息技术测量微射流

 用脉冲激光同轴全息技术建立了全息照相系统和高精度同步时序系统，获得了采用爆轰加载产生高速运动的微射流全息图，并再现出微射流的全息像，得到粒子的大小和分布情况，从图像处理得到粒子尺寸的统计结果表明，最大尺寸在300μm左右，最小尺寸在30μm左右。证明了研制的全息系统和测试技术可以测量高速的微射流场。 .     

Potential of digital holography in particle measurement

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.