基于超表面材料的扇出衍射光学元件

提出一种基于电介质纳米砖阵列的扇出衍射光学元件的设计和实现方案,其纳米砖的深宽比低至1.5。这种扇出衍射光学元件被一束波长为633 nm的入射光束照射时,可以在远场中得到均匀的4×4点阵,发散角为32°×32°,且数值模拟与实验结果吻合良好。基于超表面材料的扇出衍射光学元件具有连续、精确的相位操纵能力和较高的偏振转换效率,并且仅需一步光刻制造工艺,可以广泛应用于工程光学的各种领域,例如光学传感,激光雷达,激光加工等。     

Optical depth and multiple scattering depolarization in liquid clouds

In this paper, we calculate multiply scattered lidar signals with Monte Carlo method for measuring optical depth (extinction coefficient), effective size of water droplets, and liquid water content of clouds, and present algorithms that implement our method. We calculated multiply scattered lidar signals for various water droplet sizes and liquid water contents using a Monte Carlo method. A simple correspondence between water droplet optical depth and the degree of polarization in a modified gamma size distribution (C₁ cloud) is found. We also calculated the degree of polarization of a lidar signal for a given liquid water content, finding that the degree of polarization is only dependent on optical depth. Since the Raman lidar signal of liquid water depends on the total volume of the water droplet, the effective radius of the water droplet can thus be recovered from the degree of polarization of the lidar signal and the Raman signal of the liquid water.     

偏振-米散射激光雷达对卷云的探测

 研制了一台偏振-米散射激光雷达,用于卷云和沙尘气溶胶后向散射光退偏振比的探测研究。介绍了偏振-米散射激光雷达的探测原理,叙述了偏振-米散射激光雷达的结构、技术参数、测量方法和数据处理方法。给出了偏振-米散射激光雷达对合肥市西郊上空卷云的结构、退偏振比垂直廓线以及光学厚度的典型探测结果,对这些结果进行了分析和讨论。初步探测结果表明,合肥西郊上空高度在6～10 km的卷云的退偏振比在0.2～0.5之间,该激光雷达可以对卷云进行有效的探测,能较好地反映卷云及其光学特性的时空分布。     

多普勒测风激光雷达风场探测结果分析

为了验证自行研制的瑞利散射测风激光雷达的性能及应用价值,将激光雷达测量的风速风向廓线与探空气球测量结果进行对比,结果吻合得较好,高度10 km以下风速最大差距3.0 m/s,20 km以下最大差距4.5 m/s;风向除拐点外标准差最大32。连续探测结果显示了强劲的西风急流和风向转换特征,急流中心的高度一般在10~12 km,中心最大风速接近70 m/s,最小风速不低于30 m/s,20 km左右拐点最小风速不足1 m/s,20 km以上风速逐渐增加 ;在20 km以下风向为西风,在270左右变化,20 km以上为东风,在90左右变化。探测结果表明瑞利散射测风激光雷达既能跟踪大尺度季节性气候特征的变化规律,又能突出小尺度瞬态气候特征的形成、演化过程。     

一种高精度偏振遥感探测方式的精度分析

检偏器的角度误差是影响偏振遥感探测精度的重要因素之一,是许多高精度定量化偏振遥感需要考虑的一个问题。在检偏器(0°,60°,120°)放置的测量系统中,当入射光偏振角接近于0°或180°时偏振测量易产生最大误差值,而偏振角接近30°,90°和150°时,偏振度的测量具有很高的精度;在检偏器(0°,45°,90°)放置方式中,偏振角接近45°的光束测量易具有最大误差值,而偏振角接近于0°,90°和135°时,角度误差对偏振度测量精度的影响很小。除了个别偏振角外,对高偏振度入射光束的偏振测量通常具有较大的偏振测量误差。因此,引进线偏振光的平均偏振度测量精度描述偏振测量装置的优劣,结果表明检偏器(0°,60°,120°)放置方式优于检偏器(0°,45°,90°)放置方式。     

基于2D微电子机械系统(MEMS)镜全向激光雷达光学系统设计

为了满足全向激光探测的需求,提出一种基于2DMEMS镜扫描的激光雷达结构。激光器通过1×6高速光开关分时地给6个扫描子系统提供光信号,6个扫描子系统探测视场叠加起来可实现360°激光探测。每个扫描子系统的扫描范围为60°×30°,其中包含一个扩展MEMS镜扫描角度的发射光学天线和一个大视场有增益的接收光学天线。发射光学天线将MEMS镜±10°的扫描角扩展到±30°,发散度小于0.2mrad;接收视场内的激光波经过接收天线在探测器上所成的半像高小于1mm,接收增益为3.65。通过计算修正后的激光雷达方程可得到发射功率20 W的激光束在工作距离100 m内的回波功率≥1 nW,结果表明该光学系统可适用于激光雷达系统。     

机载光纤多普勒测风激光雷达风场反演及实验验证

通过分析1 550 nm全光纤机载多普勒测风激光雷达系统的测量模式特征,给出飞机速度校正方法、机载系统风场反演模型和算法,实现了机载大气三维风场的反演和显示软件。利用机载激光雷达的飞行试验数据,结合实时测量的小球测风数据,进行了风场信息的反演和结果的对比印证,统计4个架次的风廓线测量结果,两者的水平风速标准偏差小于1.4 m/s,风向标准偏差小于10°,相关系数都达到0.95以上,从实验结果上验证了激光雷达的工作性能和数据反演算法的准确性。     

差分吸收测污激光雷达光路分束设计

在AML-2车载测污激光雷达中,对装有不同气体的拉曼管进行拉曼激发获得相应的强、弱吸收关波长。针对差分雷达激光发射光路转换的特点及提高雷达监测的实时性能要求,基于激光偏振调制原理提出了激光雷达光路分束设计的新方法,对该方法可行性进行了理论分析,并对改进光路的能量损失进行了估算,模拟结果显示改进后的系统延长了仪器的使用寿命,提高了测量的实时性。为提高差分激光雷达实时监测性能提供了一种新方法。     

双折射器件对机载激光雷达偏振探测影响的研究

根据膜层理论给出了机载激光雷达回波信号垂直入射偏振棱镜时偏振平行分量透过率的数学解析表达式,定量分析了偏振棱镜对机载激光雷达回波信号平行分量透过率的影响,理论计算表明：棱镜晶体厚度、空气膜层厚度及棱镜结构角共同影响回波信号通过偏振棱镜的透过率;当回波信号波长为532 nm,利用1/2石英波片测得的偏振平行通道和偏振垂直通道的增益比k为1.2时,机载激光雷达偏振通道增益比k的真实值在1.003～1.463之间,若不考虑1/2波片对k值的影响,会给退偏振比反演带来较大的系统误差.     

1/2波片对机载激光雷达偏振探测影响的研究

利用平面平行板模型和晶体膜层理论定量分析了1/2波片对机载激光雷达回波信号偏振探测的影响。计算结果表明:当入射光波长为532nm时,1/2石英波片对机载激光雷达回波信号平行分量与垂直分量透过率比值的影响幅度为0.82～1.196,1/2方解石波片对机载激光雷达回波信号的平行分量与垂直分量透过率比值的影响幅度为0.86～1.27;若用1/2石英波片测得的k=1.2,当考虑石英波片对五的影响时,则偏振探测两通道k的真实值应在1.003～1.463之间;若用1/2方解石波片测得的k=1.2,当考虑方解石波片对k的影响时,偏振探测两通道k的真实值应在0.945～1.395之间。由于1/2波片对k的影响,使机载激光雷达反演得到卷云等探测目标的退偏振比有较大的系统误差。     

用于机载激光雷达偏振通道增益比测量的1/2波片优化设计

 利用平面平行板模型和晶体膜层理论,定量分析了偏振光通过1/2波片时偏振平行分量和偏振垂直分量透过率的比值与晶体厚度的关系,对用于机载激光雷达偏振通道增益比测量的1/2石英波片和1/2方解石波片的最佳加工厚度和合适的厚度加工区域进行了定量计算和探讨,指出了不适合加工的晶体厚度区域。回波信号的偏振化方向与1/2波片的光轴方向平行和垂直时分别测得的增益比值存在一定的差异,利用这两个增益比值反演得到的沙尘退偏振比,其最大相对误差在20％左右。     

基于双AOTF的新型成像光谱偏振探测系统

声光可调谐滤波器(AOTF)具有体积小、波长稳定性好、扫描范围宽、调制速度快等优点,在光谱成像中被广泛应用,但单独采用AOTF的成像光谱偏振探测还较少。为此提出只采用两个AOTF的成像光谱偏振探测新方法。该方法首先通过分束镜将入射光分成两束,两束光分别通过两个AOTF,而两个AOTF的正一级衍射光的偏振方向互成45°,由于AOTF的正一级衍射光的偏振方向互相垂直,因此两个AOTF的正负一级分别可得到0°,45°,90°和135°的光强,在测量中需保持两个AOTF的滤光所对应的波长完全相等。最后通过对两个AOTF的正负一级衍射成像,最终得到Stokes偏振信息中S₀(0°和90°光强和)、S₁(0°和90°光强差)和S₂(45°和135°光强差),结合相应的理论公式对被测目标的线偏振度(DoLP)和线偏振角(AoLP)实现成像。再通过对AOTF的射频驱动进行扫频,实现对被测目标不同波长偏振成像,最终实现成像光谱偏振探测。并通过对500,550和600 nm偏振成像进行实验验证。该方法具有无运动部件、无需转动、一次测量同时获得成像光谱偏振信息的优点。     

银川上空大气气溶胶光学特性激光雷达探测研究

小型米散射激光雷达是广泛使用的探测大气气溶胶光学特性的有效工具。作者研制了一台小型米散射激光雷达,并利用该激光雷达于2009年4月1日至4月10日期间对宁夏银川地区(北纬38°29′, 东经106°06′)上空的大气气溶胶光学特性以及时空分布进行了观测。系统选用532 nm波长激光作为光源,采用Fernald法对接收到的大气回波信号进行反演,得到了气溶胶消光系数的高度分布廓线及24 h内气溶胶消光系数相对浓度的时空变化特性;并对期间一次明显的沙尘天气进行了观测和分析。观测结果表明,该小型米散射激光雷达能够对大气气溶胶及其时空分布情况进行有效、连续的观测,其观测结果有利于分析该地区气溶胶及沙尘天气的变化趋势。     

Dual-beam coaxial amplification system of stimulated Brillouin scattering based on polarization control technology

In the field of Brillouin lidar, it has very important significance to find one method that can amplify the Brillouin scattering signal in real time. One new-type Brillouin lidar detection system based on Nd:YAG pulsed laser and polarization control device is designed in this paper. The key point of this detection system is to have two pulsed coherent lights with same frequency, same polarization and same initial phase, of which one beam is taken as the detection wave for generating stimulated Brillouin scattering signal and the other beam is taken as pumping wave for real time and effective amplification of stimulated Brillouin scattering signal. This detection system mainly includes two pulsed lasers and one electro-optical polarization controller. The laser is mainly used to obtain the pulsed lights with same frequency and same phase, and the polarization controller is mainly used to change the polarization state of two coaxial beams to make them change into same polarization state from orthogonal polarization state thus to enable the pumping wave to amplify the backward stimulated Brillouin scattering signal. It is shown from the experimental results that the adoption of this new system can realize the effect of pumping amplification and can increase the signal to noise ratio to a certain extent.     

Mie-Rayleigh Doppler Wind Lidar with Two Double-edge Interferometers

The Mie-Rayleigh direct detection Doppler lidar (DDDL) with two double-edge etalons is presented. Fabry-Perot (F-P) etalon is used as the spectral analyzer for Doppler measurement formthe aerosol and molecule backscattered signals. The aerosol and molecular backscattering signals are separated by a polarization isolator with less signal decrement, so this system has about same accuracy as individual Rayleigh Doppler lidar or Mie Doppler lidar system. The simulation on a proposed ground-based DDDL at 532 nm shows that the velocity error is less than 2 m/s below 8 km for a 100 m vertical resolution by Mie channel and 2m/s up to 20 km by Rayleigh channel, respectively.     

车载测污激光雷达对大气边界层气溶胶的斜程探测

利用自行研制的车载测污激光雷达系统 (AML 1)对大气边界层气溶胶进行了斜程探测 ,并给出了与之相应的数据处理方法。将该雷达相近时间内斜程测量与垂直测量的数据进行对比 ,结果表明此斜程探测及数据处理方法是合理可行的。文中列举了某斜程方向 (2 0°天顶角 )气溶胶随时间的演化图 ,以及某垂直剖面内气溶胶消光系数二维扫描图 ,这些典型结果很直观的反映了气溶胶时、空分布情况 ,对实现连续、实时、大范围污染监测有重要意义。     

Mie-Rayleigh Doppler Wind Lidar with Two Double-edge Interferometers

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Measurement of water cloud particle size with a dual-polarization pulsed bistatic lidar

A new bistatic lidar was developed for measuring water cloud particle size at the base of lower clouds. The lidar uses a pulsed Nd:YAG laser at 532 nm and a receiver having a polarization analyzer located at a suitable scattering angle. Cloud particle size (mode radius of the assumed size distribution) was derived from the ratio of the polarization components of the scattered light based on the single scattering Mie theory. The experiment was performed on board the research vessel Mirai in the northwestern Pacific. Particle size at the bottom of maritime cumulus and stratus was measured, and the difference between the internal structures of cumulus and stratus was observed. The effect of multiple scattering was studied by changing the observing scattering angle. The effect was not significant when the penetration depth was less than 50 m.     

Experimental determination of the calibration factor of polarization-Mie lidar

A ground-based polarization-Mie lidar has been developed to measure backscattering signals from the atmosphere and linear depolarization ratios at 532 nm. To retrieve depolarization properties of clouds and aerosols, the calibration factor (k) of two polarization channels at 532 nm must be calculated. In this paper three different experimental methods are presented to determine the calibration factor (k) in this polarization-Mie lidar. Some measured examples are presented and discussed. Experimental and validated results indicate these methods are feasible.