动态散斑与多普勒效应相互联系的分析

以散射、干涉及衍射为依据,对动态散斑及多普勒效应成因进行了分析,研究两种物理效应的理论基础及相互关系,用实验方法说明散射及动态散斑间的内在联系,进一步通过分析物体表面散射元数目对两种物理效应的约束能力来佐证两种物理效应的关联性。通过分析得出,在激光多普勒条件下,两种物理效应在本质上具有一致性,多谱勒效应能造成散射光强度振荡,这种强度振荡与动态散斑场的强度起伏密切相关。     

激光偏振成像散斑统计特性和抑制方法研究EI北大核心CSCD

对激光偏振成像系统的散斑统计特性及其相应的散斑去除方法进行了理论和实验研究。运用穆勒矩阵法建立了该激光偏振成像系统散斑光强的概率分布模型。针对现代电荷耦合器件(CCD)的成像特点,通过比较散斑与像素的大小,将散斑分为两种情况进行研究,即小散斑和大散斑。得出散斑的归一化方差与像素成线性关系,均值不受像素的影响。进而提出了统一的散斑噪声概率模型,即改进的伽马分布模型。基于此模型,提出了改进的贝叶斯非局部滤波模型。通过处理真实的偏振图片,综合等效视数、边缘增强指数等指标,表明该算法比传统的散斑去除算法具有更好的散斑去除和边缘保持能力。     

水下多粒子场激光偏振特性研究

水中粒子偏振效应的变化对激光水下探测领域的研究具有重要意义。针对不同粒子多次散射对后向散射光强以及偏振度的影响规律问题,基于激光偏振特性理论,通过实验测量的方法,对比分析了线偏振激光入射不同气泡大小和不同气泡数密度形成的气泡幕、不同气泡幕所在距离、洁净水与混浊水、不同入射角度情况下回波信号在强度和偏振度特性上的差异性,验证了水下激光偏振特性变化用于激光水下探测领域的可行性。     

强湍流效应下激光大气传输短曝光光斑统计分析

利用数值模拟的方法,对强湍流效应下激光大气传输焦平面短曝光光斑的统计特性进行了初步分析,并与实验结果进行了对比。结果表明:在强湍流效应下,焦平面短曝光光斑破碎成一系列的小光斑,这些破碎光斑的等效半径与爱里斑半径近似相等;接收器中心置于光轴轴心处,当接收孔径等于爱里斑直径时,接收的均值光强最大。     

多点协同动态散斑的统计特性

激光散斑被广泛应用于生物医学,成像探测以及无损检测等应用中,为了提升目标在环系统中基于散斑统计特性反馈远场激光聚焦光斑质量的评价效率和精度.提出了多通道协同探测的方法获得回波散斑信号的时间空间融合评价因子,并对散斑场统计理论、多点协同探测系统模型和散斑时间与空间频谱融合统计特性展开深入研究.首先,利用单点探测器探测动态...     

水下激光探测系统的水体后向散射光计算与光学参数估计

针对水下激光探测系统的水体后向散射光的计算,给出了系统的光学几何结构,分析了不同距离处的激光光斑与接收视场区域的位置变化关系并进行了定量计算。依据光传输理论建立了水体后向散射光的计算模型,根据模型的算法步骤编写了计算机程序。结合水下激光探测系统的具体参数进行了实例计算,绘制了后向散射光信号波形,并与试验获取的信号波形对比分析,验证了算法的可行性和正确性。研究了使用实测后向散射光信号数据估计水体光学特性参数的方法,通过估算的参数重新绘制曲线并反向叠加在测量数据曲线上以抵消水体后向散射光对目标信号的影响从而能够提取目标信息。     

界面反射超声散斑统计特性

对粗糙界面反射超声散斑场的一阶和二阶统计特性进行了理论和实验分析。在假设条件下,理论分析的结果表明反射空间中超声散斑的振幅和相位分别服从瑞利分布和均匀分布,而且用聚焦探头所接收的超声散斑的平均横向尺寸仅取决于测量系统的特性,与散斑的空间位置无关。为验证理论分析结果,作者建立了专门的实验系统,用圆形孔径聚焦探头接收从粗糙液－固界面上反射在不同空间位置上的超声散斑信号。实测数据显示假设条件是合理的,理论分析是正确的。     

高能激光自主自适应光学系统及激光散斑效应

设计了高能激光自主自适应光学系统,利用高能激光的主动照明探测方式对目标进行探测。由于接收到的探测回波光场受散斑效应的影响,因此建立了探测系统的物理模型,具体分析散斑效应的影响。通过散斑光强自相关函数,理论上分析确定了散斑的平均尺度;通过部分相干理论,研究了该系统接收面散斑孔径积分场复相关函数并讨论了不同散斑天线尺度比情况下的积分场复相关函数宽度;分析了目标的成像放大率和理想分辨率,讨论了物像尺度与焦平面光斑尺度之间的关系;通过系统的数值仿真,分析了不同尺度散斑对焦平面光斑阵列的影响;叠加大气湍流,确定了散斑场对大气湍流探测的影响。结果表明散斑尺度介于阵列子孔径和大孔径尺度之间为最佳设计,此时较高的位移测量精度和整体探测率可以兼得。     

合成孔径激光成像雷达散斑天线接收特性分析

合成孔径激光成像雷达(SAIL)时空散斑效应严重影响了成像质量。在时空散斑效应基础上,分析了合成孔径激光成像雷达中的散斑天线接收特性,建立了光学接收天线散斑孔径积分场的物理模型,模拟了目标分辨单元光学接收天线散斑孔径积分场距离向时间变化、方位向空间变化的二维分布。分析了不同接收天线散斑尺度比、不同天线积分起始位置对接收天线散斑孔径积分场的影响,并根据其统计性质得到散斑效应影响较小的接收天线尺寸和接收天线积分范围,为合理设计散斑效应较小的接收天线尺寸提供了参考,对进一步分析时空散斑效应如何影响SAIL目标成像有直接意义。     

舰船尾流气泡层散射相位函数及其后向散射信号特性分析

根据实测舰船的尾流气泡分布模型,利用米氏理论计算得到尾流气泡层的散射相位函数,并将其应用于尾流气泡层后向散射光接收信号的Monte Carlo仿真分析中,以便为实际海况下的舰船尾流气泡层后向散射光探测的实验设置与信号预测、分析提供可靠的依据.通过对不同距离处尾流气泡层的散射相位函数及后向散射光接收信号特性的分析,可以得出:尾流中气泡层散射相位函数的变化小明显,且对接收信号的影响较小;气泡数密度的变化导致的多次散射效应和气泡层衰减系数的变化是引起后向散射光强度变化的主要原因,数密度越大,散射光信号中的多次散射光成分越大;当气泡层厚度达到一定倍数的衰减长度时,继续增加气泡层厚度对后向散射接收信号的影响较小.     

Research for Signal Power Spectrum Distribution in Laser Doppler Rotational Speed Measurement

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高空遥测激光多普勒检波系统研究

为解决远距离处人工地震波的检测问题,研究了光源的相干性,系统的稳定性．激光多普勒信号强度、信噪比,位移测量灵敏度和精度等理论及方法。采用在腔内捕人两个直径为1．8mm的可变光阑和输出光的准直结构(4倍)．增大光源的相干长度和可测距离;在两路光中分别加入声光调制器和λ/4波片．实现偏振态匹配并使系统工作更稳定,提高信噪比;采用透镜聚焦接收．增大信号强度;采用特伦逆向反射装置,消除它在位移或振动过程巾因偏摆或横移所带来的影响,使测量灵敏度和精度提高约一倍。将此系统用于2m处的振动进行原理性实验,其振幅测量相对误差为0．1％,可测频率最高为750Hz,因此可用于高空遥测人工地震波。     

Demonstration of a spatial-spectral holographic LIDAR range-Doppler processor

We present a new approach to laser interferometric Doppler and ranging (LIDAR) processing using spatial-spectral holography (SSH). In this approach, broadband optical signals from a random noise or frequency-modulated laser are transmitted and reflected off remote targets. The return signals interfere spatially and spectrally with a local copy of the original transmit signal in an SSH medium, resulting in spectral gratings that have a spectral period inversely proportional to the LIDAR target's range and a position proportional to the target's Doppler (or velocity). These gratings are subsequently read out by a slowly chirped source onto a parallel detector array, and the velocity and range of the targets are inferred. We present the theoretical framework that describes the function of the LIDAR processor, as well as proof-of-concept experimental results.     

Rotation of a Fine Particle with Circularly Polarized Anti-Parallel Collinear Laser Beams

We have succeeded in the operation of rotating a fine particle which was held without mechanical contact by circularly polarized laser beams with opposite propagation directions. A polystyrene latex particle 11.9 μm in diameter deformed in a disk-like shape was dispersed in water, and was trapped using the anti-parallel collinear laser beams which were set up so that they had the circular polarization rotating in the same direction. It was observed that the trapped particle rotated in the same direction as the rotation of the circular polarization of light. Inversion of the rotational direction of the circular polarization of light reversed the direction of the rotation of the particle. Although the rotational speed of a particle varied significantly from particle to particle, it was found to be proportional to the laser beam intensity. A typical value for the rotational speed per beam intensity was 2.1 Hz/W.     

天基激光告警系统成像特征及信噪比研究

目标成像特征和信噪比是天基激光告警系统优化设计、目标检测及攻击事件判定的重要依据.在介绍告警系统结构的基础上,分析计算了攻击激光成像光斑的情况,并进行了实验验证,讨论了系统的背景光噪声环境,计算了入瞳处的背景光辐照度,推导了系统成像信噪比公式,并得到了攻击激光成像信噪比.结果表明:攻击激光在正入射情况下的理论光斑直径约...     

Optical energy balance in laser-produced plasmas

Optical energy balance in plasmas produced by irradiating solid targets by highpower laser pulses, has been experimentally determined. The total light scattered has been measured as a function of the laser intensity and the irratiated spot diameter. It has been found that the net light absorption does not depend on the laser intensity alone, but is also affected by the irradiated spot area. It has also been observed that diffuse back reflection becomes a dominant loss mechanism at high incident flux and small irradiated spot area.     

激光偏振特性对丙酮和氧气多光子电离质谱信号的影响

在极性分子丙酮复合物CH3COCH3*H2O和非极性分子氧气的REMPI谱中,母体离子信号强度与激光偏振方向的关系是不同的.改变532 nm激光偏振方向,记录了两种分子母体离子信号强度,实验结果表明,对于氧气分子的母体离子信号强度,激光偏振方向的改变对其没有影响,而对于CH3COCH3*H2O的母体离子信号强度,随偶极矩与激光偏振方向夹角的增加,其母体离子信号强度呈余弦曲线变化,且与夹角余弦的2.1次幂成正比.理论分析显示,CH3COCH3*H2O的REMPI母体离子信号强度应与此夹角的余弦的2次幂成正比.这就说明实验结果和理论分析是相符的.     

Linearity of quadrant avalanche photodiode in laser tracking system

The tracking precision of laser tracking system is affected by the angular resolution of quadrant avalanche photodiode. According to the detecting principle of quadrant avalanche photodiode, the light spot area, the optical intensity distribution, the non-uniformity of response, and the signal-to-noise ratio （SNR） that affect the linearity of the detector are studied. The light optical spot area and the optical intensity distribution can be adjusted through software. The non-uniformity of response and the SNR are influenced by the noise of the detector. Because the noise is affected by the optical intensity of the incident laser, it is difficult to obtain the law of the linearity caused by noise. When the light spot area and the optical intensity distribution are fixed, the other factors can be measured. With the detector scanned in raster scanning mode, the non-uniformity of response is measured at different SNRs. The linearity of detector is measured by a moving target that can reflect the illuminating laser to the detector in diffuse reflection mode. The nonlinear error of the linearity of detector can be minimized by increasing the SNR.     

Impact of an extended source in laser ablation using pulsed digital holographic interferometry and modelling

Pulsed digital holographic interferometry has been used to study the effect of the laser spot diameter on the shock wave generated in the ablation process of an Nd:YAG laser pulse on a Zn target under atmospheric pressure. For different laser spot diameters and time delays, the propagation of the expanding vapour and of the shock wave were recorded by intensity maps calculated using the recorded digital holograms. From the latter, the phase maps, the refractive index and the density field can be derived. A model was developed that approaches the density distribution, in particular the ellipsoidal expansion characteristics. The induced shock wave has an ellipsoid shape that approaches a sphere for decreasing spot diameter. The ellipsoidal shock waves have almost the same centre offset towards the laser beam and the same aspect ratio for different time steps. The model facilitates the derivation of the particle velocity field. The method provides valuable quantitative results that are discussed, in particular in comparison with the simpler point source explosion theory.     

Depolarization characteristics of incompletely polarized and partially coherent laser beams in slant atmospheric turbulence

Based on the cross-spectral density function of transmission theory and the unified theory of coherence and polarization, the depolarization characteristics of incompletely polarized and partially coherent laser propagation in slant atmospheric turbulence are investigated. According to extended Huygens–Fresnel principle, the analytical expressions for intensity and degree of polarization in the slant path are derived. The effects of the wavelength, the initial spot size and the transmission distance on the intensity and degree of polarization are described. The results show that a more stable distribution of the degree of polarization at the receiver is obtained with increasing wavelength for a certain receiver height. The conclusions play an important role in optical communications and target recognition.