OFLID: Simple method of overlap factor calculation with laser intensity distribution for biaxial lidar

We proposed a simple overlap factor calculation method based on laser intensity distribution (OFLID), which is simple, practical and can be applied to any specific laser intensity distribution. In order to obtain the laser intensity distribution and parameters of our laser system, we designed a simple experiment to measure them, and then simulated an ideal Gaussian and uniform laser intensity distribution with the measured parameters. The OFLID calculation results indicated that the overlap factor of the measured distribution has approximately half the relative error of that of the ideal Gaussian distribution in the increasing range field for our lidar. Specifically, the laser intensity distribution should be regarded in the overlap correction of the lidar signal. Theoretically, the OFLID method can reduce the error caused by the hypothesis of ideal uniform or Gaussian intensity distributions in the analytical method. In addition, the method is easy to implement for overlap correction, signal simulation and system configuration optimization for biaxial lidar.     

Study on Search after Central Position of Laser Speckle

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Size measurement of nanoparticles using the emission intensity distribution of laser-induced plasma

A two-dimensional optical imaging method is presented for monitoring the laser-induced breakdown events of aqueous nanoparticles. The method is based on measuring the light intensity distribution of plasma from spatially resolved breakdown events. The number of laser breakdown events as a function of the emission intensity follows the Gaussian distribution and its full-width at a half-maximum appears in direct correlation with the particle size. Hence the particle size can be determined by measuring the plasma emission intensity distribution. Calibration of the method is carried out with reference polystyrene particles dispersed in water. Application is demonstrated for measuring bentonite colloidal particles of different sizes in groundwater. PACS 42.62.Eh; 52.25.Rv; 52.70.Nc     

基于瑞利-索墨菲积分的大角度激光分束器设计

针对目前激光分束器只能产生小发散角的问题,基于严格的非傍轴近似的衍射积分公式,提出了一种大发散角分束器的设计方法.先对目标光场分布进行坐标和光强修整,再利用改进的GerchbergSaxton迭代算法得到所需分束器的相位分布.分别采用本文设计方法和原有方法设计了发散全角为40°×40°的5×5分束器,仿真和实验结果表明:原有方法设计得到的5×5子光束存在着显著的枕形畸变,并且光强分布不均匀.而本文方法设计得到的子光束呈均匀等间隔排列,并且强度分布更为均匀.     

Depth of focus estimation based on exposure dose distribution

A defocusing exposure dose distribution model is established with the integral effect of light intensity on time taken into account for laser direct writing on a thin photoresist with total reflection substrate. Exposure dose distribution curves are established using the established model for different photoresist depths. A side slope angle is established for each defocusing amount in accordance with the exposure dose distribution curves, and so depth of focus can be estimated by simply checking to see if the maximum side slope angle with the horizontal is in the range of 80-100°. Simulation results indicate that when laser direct writing is done on a thin photoresist with total reflection substrate using a laser with wavelength equal to 442 nm and a lens with numerical aperture equal to 0.5, the depth of focus estimated using the proposed method is 1 μm, which is just 1/3 of the depth of focus estimated using the method based on intensity distribution. It is therefore concluded that it is the integral effect of light intensity on time that causes the depth of focus estimation error, and the proposed method can be used to achieve a more accurate depth of focus estimation compared to the intensity distribution based method.     

基于图象亮度分布的环形干涉条纹判读法

提出了一种基于图象亮度分布的环形干涉条纹判读法,定义了干涉条纹亮度的水平分布和竖直分布,利用干涉条纹亮度的水平分布和竖直分布计算出干涉条纹中心,根据此中心,进一步提出了基于布莱森汉姆(Bresenham)圆弧生成法和正负圆弧生成法的条纹亮度分布,由此得到所需条纹宽度,即可计算出物体的精确位移.     

大长宽比矩形有源非稳腔模式的数值模拟

 利用快速傅里叶变换算法和薄层增益近似方法,在Matlab计算平台上,对大长宽比正支共焦有源谐振腔进行了数值模拟。得到了长宽比为3.6∶1的大功率化学激光器输出的近场模式强度和相位分布,以及理想聚焦下的远场光斑的强度分布。给出了由非均匀增益引起的强度分布不均对远场光斑的影响。得到的近场图像结果和实验结果基本一致,表明本方法可以对大长宽比矩形腔的输出模式进行仿真,从而为激光器的光束质量改善提供计算参考。     

用光谱诊断技术测定高能单元推进剂的温度分布

采用光谱诊断技术中的相对强度法测定了单元推进剂六硝基六氮杂异伍兹烷(HNIW)在3 MPa和5 MPa两种压力下的燃烧火焰温度分布。结果表明,相对强度法能准确地测出单元推进剂HNIW在整个燃烧过程的温度分布曲线,测得的最高燃烧火焰温度低于相应压力下的理论计算温度;测量压力升高,最高燃烧火焰温度更接近于理论计算温度。此实验结果说明：在较高压力条件下,用相对强度法能够准确地测定高能高燃速推进剂的燃烧火焰温度分布。     

均匀球形液滴二阶和五阶彩虹的重建及应用

从理论和实验两方面研究了不同温度下球形液滴的彩虹强度分布及在粒度测量中的应用。研究结果表明折射率为 1.33附近液滴在 117°～ 134°散射角范围内的散射强度分布不是单一的二阶彩虹强度分布 ,而是二阶和五阶彩虹的干涉强度分布。基于散射强度频谱特点 ,提出了一种从干涉强度谱中重建二阶和五阶彩虹强度分布的方法 :逆快速傅里叶变换 (IFFT)。利用洛伦兹米理论 (LMT)模拟计算了温度为 2 0℃和 80℃下水粒子二阶彩虹的高频结构与粒子直径的关系 ,获得了经验公式。该关系式可用来测量确定温度下均匀水粒子直径。还利用激光彩虹测试系统测量了水柱二阶彩虹角度范围内的散射强度分布。上述理论研究结果与实验结果进行了比较 ,两者吻合得很好。基于上述研究 ,可以从单一阵列探测器获取的彩虹信号提取不同阶次彩虹分布 ,用于液滴多参量的反演测量。     

The research of phase-locking of more discharge tubes for two-dimensional axisymmetric-fold combination resonator CO2 laser

A method of reflection-injection phase-locking used on two-dimensional axisymmetric-fold combination resonator (ASFC) CO₂ laser has been proposed. The structure characteristics and the method of phase-locking have been introduced. The expression of output light intensity distribution has been deduced by matrix theory and Collins Formula and the output light intensity distribution has been numerically calculated and simulated. Comparing the output light intensity distribution in the case of phase-locking with that of non-phase-locking. The result shows that this method of phase-locking greatly improve the characteristics of output beam.     

分数傅里叶变换面上余弦-高斯光束的变换特性

 利用Wigner分布函数的方法，研究了余弦-高斯光束的分数傅里叶变换特性。导出了余弦-高斯光束在分数傅里叶变换面上光强分布和束宽的解析计算公式，并对此进行了数值模拟计算。研究表明：分数傅里叶变换阶数对余弦-高斯光束的光强分布有明显影响，余弦-高斯光束的轴上光强随分数傅里叶变换阶数呈周期性变化，束宽随分数傅里叶变换阶数也呈周期性变化，周期为2；对给定调制参数的余弦-高斯光束，通过适当选取分数傅里叶变化阶数可以获得平顶的光强分布。     

激光频宽理论极限计算方法的讨论

本文讨论了光强非均匀分布的单模激光腔的输出频宽的计算方法。并针对腔内光强分布的两种不同模型,分析了频宽修正因子。     

基于étendue量的液晶投影物镜相对照度分析

基于非成像光学的étendue量对液晶投影显示照明系统和投影物镜进行匹配,对液晶投影物镜的相对照度进行分析,根据étendue量计算照明系统液晶板照明面的发光强度分布,与根据朗伯体服从余弦分布的计算相对照度的算法进行比较,并对相对照度的Rimmer算法进行修正,分析和实验表明,修正算法得到的投影物镜相对照度计算更符合实际情况,对于投影物镜确定渐晕系数、校正像差有利.     

一种新的Fabry-Perot干涉条纹处理方法

介绍了一种提取Fabry-Perot(法布里-帕罗)干涉条纹圆心点坐标和条纹半径的新方法。首先对干涉图像依次进行二值化处理,对所得到的条纹强度曲线进行均平滤波和自适应滤波,根据条纹灰度值强度余弦函数分布的特点,对条纹灰度值数据进行最小二乘法拟合,获得条纹强度峰值坐标,通过精确的迭代算法,进而获得Fabry-Perot干涉条纹圆心点的坐标;然后再对干涉条纹进行圆周积分,从而可以确定每级Fabry-Perot干涉条纹的半径长度。该方法可提高计算精度,减小计算误差。     

空间外差光谱仪干涉图非均匀性校正研究

空间外差光谱仪在研制加工过程中,由于加工误差及胶合误差会使CCD接收到的干涉图存在光强分布不均匀现象,降低了变换光谱的准确性。基于对空间外差光谱仪干涉图光强非均匀性的产生机制与特点分析基础上,提出了一种干涉图非均匀性校正方法,该方法通过对实际干涉图进行单调分解、分段归一化及重新组合过程求解出光强分布函数,然后将变换光谱与光强分布函数倒数的傅里叶变换结果进行卷积来获得非均匀性校正后的光谱,最后将校正光谱进行逆傅里叶变换从而实现干涉图的非均匀性校正。将此方法应用于空间外差试验仪的近红外实测单色光干涉图的非均匀性校正,结果显示,该方法可以有效改善干涉图光强分布的非均匀性,抑制变换光谱的边频信号,通过与仿真的理想光谱对比,1 571和1 572 nm光谱校正前后噪声的减小率分别达到40.7%和24%,提高了光谱信噪比和准确性。     

基于LabVIEW的LED三维特性检测的研制

为了解决传统配光曲线只能反映LED发光二维特性、立体感太差及不便于人为观察比较的难题,提出一种新的基于高级图像编程语言(LabVIEW)的LED三维特性(光强空间分布)快速检测方法。在传统光强空间分布检测方法的基础上,采用多路光度探测单元同步测试,可在0.2s内一次性由31个探测单元同步测得LED光源的二维光强空间分布（配光曲线）。通过增加旋转机构转动待测LED样品,依次测得i(i=180°/α)条配光曲线。最后由自研软件将i条配光曲线进行数据汇总处理,便可得到LED光源的光强空间分布的三维立体图。该检测方法具有速度快、精度高、信息量大等优点,并且具有实时性和直观性。     

Method of reconstructing wavefront aberrations from the intensity measurement

A method for reconstructing wavefront aberrations from intensity measurements in the focal plane of a focusing optic is presented. This reconstruction method is simple, fast, and accurate in reconstructing wavefront aberrations because it uses the inverse Fourier transform of an intensity distribution in the focal plane with a reference electric field. The validity of the reconstruction method is demonstrated by computing a wavefront aberration from the intensity distributions in the focal plane.     

基于二元光学设计的高能激光窗口的初步探讨

对非均匀近场强度分布影响强激光远场聚焦效果的原因进行了分析。对高能激光窗口进行了二元光学设计。提高了光束强度分布的均匀性,改善了光束质量。介绍了二元光学设计的基本原理,采用随机并行扰动爬山法对窗口的位相分布、变换后的光束强度分布、衍射效率和光束均匀性进行了计算。计算结果表明,基于二元光学设计的激光窗口能有效地改善光束强度分布的均匀性,提高了发射光束的质量。     

A theoretical and experimental investigation of sound intensity distribution within a splitter silencer

Results are presented of an investigation into the sound intensity distribution in a ventilation duct splitter silencer subject to plane waves incident in the axial direction, under conditions of zero flow. A theory is developed which accounts for the generation of nonplane fields at the cross-sectional discontinuities of the duct-silencer-duct system. A local reaction model of the splitter material is employed, and analytical solutions and numerical results are presented for the sound intensity distribution within the silencer. Experiments were conducted to measure the distribution of sound intensity in a silencer subject to incident plane waves. The conventional cross-spectral method of measuring sound intensity could not be used because of the practical difficulties in manoeuvring the two-microphone assembly through the narrow air passage and obtaining measurements at positions close to the wall of the splitters. Instead, a modified cross-spectral method was devised which employs only one microphone for measurement. In this method, the transfer functions between the loudspeaker input signal and the microphone output signal were measured at an array of microphone positions within the air passages of the silencer. The divergence equation for sound intensity was employed to infer transverse intensity distributions from the computed axial distribution. Reasonable qualitative agreement is obtained between theoretical and observed sound intensity distribution, but the local reaction model of the splitter is found not to be satisfactory at the lower frequencies.     

圆锥透镜对球面入射光的聚焦衍射特性

首次导出了圆锥透镜对球面入射波的聚焦衍射计算公式,分析了其轴上能量分布与横向场能量分布特性. 数值计算结果表明,选择合适的球面入射波可以扩展焦深,改善光强分布,同时保证横向场能量分布要求. 对于半径20 mm,锥角θ=1×10^－2的圆锥透镜,采用曲率半径为1200~1400 mm的球面入射波,可扩展焦深200 mm到120 mm,光强的均匀性有明显改善,横向场能量分布形状改变量不超过15 μm,完全达到应用要求.