大气气溶胶浓度检测及检测系统设计

提出了一种双通道交替探测透射和散射的气溶胶浓度检测方法,并设计了相应的检测装置。利用光通过气溶胶后被吸收和散射的作用,采用双光路周期性测量90°散射光及透射光光强,消除了光源老化及探测器灵敏度不同对测量结果的影响。选用MSP430单片机作为主控芯片,通过对激光管施加脉冲信号实现对光信号调制,并在探测接收端进行信号的放大及滤波,有效消除了环境因素对测量精度的干扰。采用该测量装置进行了气溶胶测量,结果显示其线性较好,线性相关系数为0.976 5,表明测量系统稳定可靠。     

大气气溶胶消光系数检测系统设计

利用半导体激光器照射大气气溶胶试样后光强衰减得到大气气溶胶消光系数。光束经过气溶胶后检测透射方向的光强值,经光电转换、信号调理、AD采样后根据朗伯比尔定理计算气溶胶消光系数。采用双通道测量气溶胶消光系数的方法,减小了由于半导体激光器光强不稳定和大气分子对测量结果的影响。对设计的系统以不同浓度的气溶胶进行了检测,其线性度良好,相对误差小于4%。所设计的大气气溶胶检测装置体积小、操作简单、探测速度快,对监测大气污染和能见度等有一定的应用价值。     

基于CCD成像的侧向散射激光雷达几何标定方法

通过分析CCD成像特点,设计了侧向散射激光雷达几何标定实验,得到CCD各像元的角宽度,并确定了CCD像元与散射光位置之间的对应关系.对两次实验中采集的回波信号进行标定,并分别与POM02进行相函数比对、与后向散射激光雷达进行探测信号比对,结果表明:相函数廓线和POM02测量结果相吻合;侧向散射激光雷达信号与后向散射雷达的距离修正信号在650m以上的变化趋势一致.侧向散射激光雷达弥补了后向散射激光雷达在近地面段不能探测气溶胶的不足,该标定方法可靠,为进一步利用侧向散射激光雷达研究近地面气溶胶的时空分布奠定了坚实的基础.     

激光雷达研制及其探测大气气溶胶的实验研究

作为一种激光探测大气气溶胶特征的新技术,采用分子滤波技术的高光变分辨率激光雷达在国际上得到了发展,给出了对这种YAG激光雷达系统的理论分析并建立了实验装置,其接收望远镜孔径为300mm,YAG激光脉冲能量为150mJ。通过数值模拟与初步测量估计了激光雷达性能,测量了大气回向散射信号,测量结果表明实结果与理论分析一致。     

南京北郊气溶胶质量浓度空间垂直分布反演

使用拉曼 米激光雷达在南京北郊进行常规性检测,通过分析激光雷达回波信号,借助气溶胶质量浓度的线性模型和指数模型进行气溶胶质量浓度空间垂直分布反演。为提高反演的精确度,对米散射信号进行近场修正,消除重叠因子的影响,拉曼散射信号进行小波分析等去噪方法处理。处理过的米散射信号用来反演0~3 km大气的气溶胶质量浓度,拉曼散射信号用来反演3 km~10 km大气的气溶胶质量浓度,然后通过2个信号拼接反演中低层气溶胶质量浓度。实验结果:2种模型反演的气溶胶质量浓度在不同时刻的相关性系数为0.991和0.973 6,具有一定的可信度。     

基于回波信号仿真的瑞利-喇曼-米激光雷达研制

 在分析瑞利、喇曼和米散射仿真回波信号的基础上,研制了一台探测大气温度、气溶胶和卷云的瑞利-喇曼-米散射激光雷达,实现了一台激光雷达针对大气温度、气溶胶和卷云光学特性的多参数探测。为提高瑞利和喇曼微弱回波信号信噪比,采用了极高灵敏度的R4632光电倍增管和光子计数技术;为实现对大气气溶胶和卷云的探测,532 nm回波信号采取高低分层技术、高层通道回波衰减方法和探测器门控技术。瑞利-喇曼-米散射激光雷达的探测结果证明了利用仿真回波信号指导激光雷达设计的可行性。     

基于CCD的侧向散射激光雷达信号提取方法

后向散射激光雷达是探测大气气溶胶空间分布的强有力手段,但由于盲区和过渡区的存在,限制了它在近距离段的探测范围和精度。基于电荷耦合器(CCD)的侧向散射激光雷达可实现近距离段气溶胶信号的连续探测,且探测精度较高。分析了侧向散射激光雷达中干扰光和背景光的特点,找到了减少它们的方法。分析了激光在大气中产生侧向散射光的特点,找到了同一距离处侧向散射光的叠加方法。应用Matlab编程实现了对信号的自动提取,并与后向散射激光雷达信号进行了实验比对,结果表明该信号提取方法是可靠的、可行的。     

偏振-米散射激光雷达的研制

研制的偏振-米散射激光雷达（PML）,可用于探测卷云和沙尘气溶胶的后向散射光退偏振比以及研究流层大气气溶胶的消光特性。采用窄带滤光片和光阑,将接收到的激光大气回波信号谱线（米散射和瑞利散射光谱）从天空太阳背景噪声中分离出来,以提高系统的白天探测能力。介绍了偏振-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。对偏振-米散射激光雷达的性能参数进行了测定,并对测定结果进行了分析与讨论,给出了偏振-米散射激光雷达对合肥市地区(117.16°E, 31.90°N)上空大气气溶胶的消光特性和卷云的结构、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。结果表明：研制的偏振-米散射激光雷达性能可靠,能对大气气溶胶和卷云的物理和光学特性进行有效的探测。     

大气颗粒物近前向光散射特性研究EI北大核心CSCD

为了考察大气颗粒物近前向光散射特性及其在粉尘质量浓度测量中的应用,建立了大气颗粒物近前向散射光测量实验装置,通过单分散和多分散颗粒物样本的实验测量和基于米散射理论的颗粒物光散射计算,得到颗粒物近前向散射光强度与粒径及分布宽度的关系,结果表明该装置可用于测量环境大气气溶胶质量浓度。通过已知参数的单分散气溶胶样品测量,借助米散射理论计算,可以获得较为准确的响应度数值,并估计测量实际大气颗粒物的误差范围。采用亚利桑那超细标准粉尘进行质量浓度定标,测量城区自然环境颗粒物的粉尘质量浓度,需要约2.5倍的修正。     

大气颗粒物近前向光散射特性研究

为了考察大气颗粒物近前向光散射特性及其在粉尘质量浓度测量中的应用,建立了大气颗粒物近前向散射光测量实验装置,通过单分散和多分散颗粒物样本的实验测量和基于米散射理论的颗粒物光散射计算,得到颗粒物近前向散射光强度与粒径及分布宽度的关系,结果表明该装置可用于测量环境大气气溶胶质量浓度。通过已知参数的单分散气溶胶样品测量,借助米散射理论计算,可以获得较为准确的响应度数值,并估计测量实际大气颗粒物的误差范围。采用亚利桑那超细标准粉尘进行质量浓度定标,测量城区自然环境颗粒物的粉尘质量浓度,需要约2.5倍的修正。     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.