应用被动傅里叶变换红外光谱技术探测生物气溶胶研究

从红外遥感辐射传输理论出发,利用二流近似方法,建立了包含散射影响的生物气溶胶被动红外探测模型;从理论上阐明了气溶胶对四周辐射的散射对生物气溶胶被动红外探测的影响。以某微生物孢子气溶胶为对象开展探测原理试验,研究了生物气溶胶红外光谱特性。给出了生物气溶胶室内吸收池试验结果,用辐射传输模型解释了试验现象。通过试验验证了探测模型的合理性、有效性;结合探测模型和室内试验结果,也可为外场试验的开展提供参考。     

基于侧向散射技术的近地面气溶胶后向散射系数廓线探测

气溶胶是大气中污染物PM2.5和灰霾的主要成分,近地面的气溶胶直接影响人们的生活和生产。利用电荷耦合器件(CCD)侧向散射激光雷达系统和相应的反演方法,对探测到的数据进行处理和分析。与后向散射激光雷达对比,验证了CCD侧向散射激光雷达探测结果的正确性。分析了2014年4月合肥西区董铺岛3 km高度范围内气溶胶后向散射系数的特点:随时间和高度变化;天气晴好时,地面上后向散射系数与地面站PM2.5质量浓度成正比;紧贴地面有一层较厚气溶胶。实验探测结果表明基于CCD的侧向散射激光雷达是探测近地面气溶胶浓度的一种有效的新方法。     

对流层气溶胶消光特性的Mie散射激光雷达探测研究

在介绍激光雷达对气溶胶探测的相关理论的基础上,对自行研制的一套1064nmMie散射激光雷达系统的系统结构、相关技术参数作了详细说明。用此系统对苏州城区对流层气溶胶进行探测并对探测结果进行了初步的分析。     

偏振-米散射激光雷达探测对流层气溶胶光学特性

利用偏振-米散射激光雷达探测对流层大气气溶胶的光学特性及其时空分布.介绍了该雷达的结构、技术参数和探测原理.获得了气溶胶的消光系数垂直廓线和光学厚度,并对这些结果进行了分析和讨论.结果表明,该雷达能较好地探测对流层大气气溶胶的光学特性及其时空分布.     

Fernald前向积分用于机载激光雷达气溶胶后向散射系数反演的理论研究

初步反演结果表明,Fernald前向积分法(FFIM)能够用于机载大气探测激光雷达气溶胶后向散射系数的反演,但相应的理论解释没见国内外相关文献报道.根据合肥地基大气探测激光雷达2008年2月27日的探测数据模拟得到的机载激光雷达数据,对FFIE用于机载大气探测激光雷达气溶胶后向散射系数的反演结果进行了定量分析,分析表明:当反演标定点的高度选在10 km左右时,FFIM能够用于机载大气探测激光雷达气溶胶后向散射系数反演的主要原因有3个:1)Fernald前向积分方程(FFIE)分母中两项的差值一般远大于零, 关键词： 大气光学 Fernald前向积分法 机载大气探测激光雷达 气溶胶后向散射系数     

探测大气温度和气溶胶的瑞利-拉曼-米氏散射激光雷达

研制了一台瑞利-拉曼-米氏散射激光雷达,实现了对流层和平流层大气温度和密度的探测。作为多参数大气探测系统,该激光雷达也实现了夜间至25km、白天至5km高度气溶胶的探测能力;其中激光雷达是探测平流层气溶胶最有效的手段之一。利用该激光雷达对目前合肥地区对流层温度、平流层逆温现象、对流层和平流层气溶胶做了探测和分析,并给出若干典型结果。分析表明,该激光雷达数据可靠,可用于大气温度、密度、气溶胶的常规观测和分析研究。     

粒子的非球形程度对消光系数的影响研究

利用中国气象局南京综合观测基地的微脉冲激光雷达对南京北郊的气溶胶特性进行了常规的观测,并计算了气溶胶的退偏振比,反演了气溶胶的消光系数,分别得到气溶胶退偏振比及消光系数廓线。分析了不同天气情况下退偏振比和消光系数变化趋势的关系,发现退偏振比和消光系数有一定的相关性,即粒子非球形的程度对其消光的大小有一定的影响。初步探测结果发现:在同一个时刻,晴天和雾霾天时二者变化趋势相同,探测到水云时二者变化趋势相反,探测到冰相云时二者变化趋势相同,研究表明:当探测到气溶胶和冰相云时,粒子的非球形特性越明显其消光系数越大;当探测到水云时,粒子越近似球形其消光系数越大。     

激光诱导生物气溶胶荧光雷达的设计与数值仿真

为了评估激光诱导荧光雷达对生物气溶胶粒子的有效探测距离及随生物气溶胶浓度变化的敏感性,在阐述生物气溶胶探测原理的基础上,设计了一台激光诱导荧光雷达。该雷达选用波长为355 nm的二极管抽运的Nd:YAG固体激光器作为激励光源,基于脉冲能量、脉冲数量、滤光片带宽、望远镜口径、接收视场角以及生物气溶胶粒子荧光非弹性散射截面积等主要参数,对生物气溶胶荧光回波信号的信噪比进行数值仿真。仿真结果表明,生物气溶胶粒子的质量分数为10-12时,在探测误差小于10%的情况下,系统在白天和夜晚的有效探测距离分别可达1.0 km和7.8 km;而在探测距离定义为0.5 km时,系统对生物气溶胶质量分数的最小分辨能力,白天和夜间分别为1.8×10-13和1.0×10-14。仿真结果有利于了解激光诱导荧光雷达系统的最优参数设定和最佳的实验环境,进而实现对生物气溶胶的有效探测。     

双视场米散射激光雷达探测对流层气溶胶

介绍了自行研制的用来探测对流层大气气溶胶消光特性的双视场米散射激光雷达.该激光雷达采用两个具有独立接收视场的探测通道分别接收高低层532 nm的大气回波信号,可以兼顾低层大视场角低探测盲区和高层小视场角高探测高度的要求.叙述了该雷达系统的总体结构和技术参量以及数据处理方法,给出了合肥地区(东经117.16°,北纬31.90°)大气气溶胶消光系数廓线和对流层光学厚度的探测结果.测量结果表明,该雷达具备昼夜连续观测对流层大气气溶胶的能力,可以很好地反映气溶胶粒子的时间和空间分布特征.     

基于MODTRAN模型使用被动傅里叶变换红外光谱技术对生物气溶胶的探测研究

利用MODTRAN模型在水平低仰角探测模式下,对生物气溶胶探测的问题进行了分析讨论.用傅里叶变换红外(FTIR)光谱技术对生物气溶胶进行探测研究.首先介绍了MODTRAN模型的大气模式和廓线,根据FTIR光谱技术对生物气溶胶的被动探测要求,利用辐射传输理论和最简单的三层模型,仿真计算得到大气背景和目标生物气溶胶之间的辐射亮度差?L,然后对?L进一步差值得到信号?2Lt,同时再结合光谱仪自身的噪声等效辐射亮度值,得到实际情况下的信号值?2Lt;最后根据探测条件和MODTRAN提供的大气模式,使用被动遥测红外光谱方法预测每种大气模式下生物气溶胶的探测限浓度.每种大气模式下探测限浓度的不同,是因为边界层温度、透过率和背景辐射亮度的不同所导致,同时还与生物气溶胶的吸收系数有关.研究表明,FTIR光谱被动遥测技术能够探测到生物气溶胶的存在,进一步说明探测生物气溶胶的可行性,也为生物气溶胶实际探测提供了一种方法.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.