用激光相位多普勒技术测量循环流化床中的颗粒运动特性

用激光相位多普勒技术测量循环流化床中的颗粒运动特性吕清刚，杨涛，潘忠刚（中国科学院工程热物理研究所北京１０００８０）关键词：循环流化床，气固两相流动，激光相位多普勒颗粒动态分析仪１引言循环流化床燃烧装置已经得到了广泛的应用，但是由于流化床内的气固两相...     

脉冲半导体激光器时基脉冲的实验对比测量

以脉冲半导体激光器为例，对3种测量激光脉冲时基抖动技术进行了对比实验。这3种测量技术分别是：基于宽带取样示波器的时基抖动测量技术;基于相位比较检相器的相位噪声测量技术和基于频谱仪的谐波频谱分析技术。对比研究发现：基于宽带取样示波器的时基抖动测量技术适用于脉冲宽带及脉冲抖动较大的光脉冲；基于频谱仪的谐波频谱分析技术适用于低重复频率光脉冲的抖动测量；基于相位比较检相器的相位噪声技术测量精度高、动态范围大、结果可靠，对于高重复频率的超短光脉冲，建议选用相位噪声测量技术测量激光脉冲的时基抖动。     

激光多普勒测速及其应用

测量气体和流体速度的传统方法是采用毕脱管或热线风速仪,其做法是在被测速度场中放置一个传感器,然后将它感受到的与速度有关的信号送到二次仪表进行处理,得到速度的信息.然而,在流场中放置一个物体,其本身就意味着要干扰流场,从而影响测量精度,而且这些方法在测量狭小流场如附面层、射流元件等方面就无能为力,它不可能测量比传感器的体积还要小的流速场速度分布. 近年来发展了一种新型的测速技术,无需接触被测流体,只要让几束细光束穿过流动的气体或液体,就能测出流体的流动速度,这就是激光多普勒测速技术. 六十年代中期,Yen和Cummins[1]…     

用于激光推进的高功率激光器的选择

 从激光推进的要求出发，阐述了用于激光推进的高功率激光器的选择原则，即激光器必须满足：（1）高的平均功率和峰值功率；（2）高的单脉冲能量；（3）高的重复频率；（4）优良的大气传输特性。主要分析了目前YAG固体激光器、自由电子激光器和TEA脉冲CO₂激光器的特点，通过上述4个方面性能的比较，认为在目前水平下，TEA脉冲CO₂激光器是进行激光推进的首选强激光源，其优点表现在：功率可达10kW量级，单脉冲能量可达0.5~1kJ，重复频率为20~40Hz；激光波长处于大气传输窗口，对大气变化不敏感；工作物质快速流动，不存在热透镜效应和破坏阈值；相关光学元件易于制造；光束质量较好；运行成本低。     

压气机转子内流场的三维LDV测量

激光多普勒测速仪（LDV）的应用日益变得广泛，由于环境条件、物理和几何上的可达性以及流动的复杂性，使人们在每个具体应用中，需要对仪器参数合理地设置和实验装置全面地考虑．通过对一个轴流压气机转子尖区内流场的反复测试，比较精细的流动结构被揭示出来．这里所阐述的LDV测量技术，在其它方面的应用中，也具有一定的普遍意义．     

自锁模钛宝石激光实现全固化运转

自锁模钛宝石激光实现全固化运转＊魏志义陈毓川李健何京良侯炜房哓军许祖彦（中国科学院物理研究所光物理实验室，北京１０００８０）邓佩珍徐军周永宗乔景文（中国科学院上海光学精密机械研究所，上海２０１８００）超短脉冲激光的实用化研究是近年飞秒技术发展的重要方...     

飞秒激光脉冲的频率分辨偏振光学开关法测量研究

建立了一台频率分辨偏振光学开关（PG FROG）法飞秒脉冲测量装置，利用该装置对“极光Ⅱ号”飞秒激光放大系统进行了测量.在利用偏振光学开关法测得的时域和频域信号基础上，结合对信号光强度分布的计算机迭代处理，得到了有关飞秒激光电场、光谱及其相位的信息；并且对系统工作在不同状态时的激光脉冲进行了测量和比较分析，给出了有关该系统较详细的电场、光谱、相位以及啁啾状况.结果显示，当系统工作在零啁啾附近时，该系统输出的激光脉冲的电场、光谱和相位分布较规则，相位起伏较小；当系统偏离零啁啾状态时，虽然电场和光谱变化不很明显，但相位分布变化剧烈. 关键词： 频率分辨偏振光学开关(PG FROG)法 飞秒激光 自相关     

自适应滤波技术在激光多普勒测速仪中的应用

激光多普勒测速仪检测系统提取的光电信号中存在较大的噪声信号。为了消除这些噪声干扰, 提高激光多普勒测速仪的测量精度,提出一种新的信号处理方法,将最小均方差自适应滤波技术应用于激光多普勒测量中,利用多普勒信号和噪声信号的统计特性,以最小均方误差估计为准则,最大程度地滤除噪声信号。阐述了最小均方差自适应滤波算法的基本原理,在MATLAB平台上将其应用于理想正弦信号进行仿真,并将其应用于实测多普勒信号的处理中。仿真和实验均表明,该技术可以有效抑制激光多普勒测量中的多频率噪声的干扰,大大提高多普勒信号的信噪比和测量精度,为设计高精度的激光多普勒测速仪创造了条件。     

纳秒激光冲击加载的全过程诊断

 与传统的冲击加载方式相比,激光驱动试样具有微尺寸（直径小于1 mm,厚度约10 μm）、超短作用过程（纳秒量级）等特点,但其速度变化历史的实时诊断颇为困难,因此发展适用于激光驱动的高时空分辨率的实时测试技术是十分重要和有价值的。采用桌面式脉冲Nd:YAG激光器作为加载平台,发展了激光加载下的小焦点多普勒光纤探针测量系统（焦斑直径约200 μm,时间分辨力约50 ps）,成功实现了从激光脉冲驱动微尺寸飞片飞行直至撞击Z-切石英试样的全过程实时诊断。实验结果显示,将6 μm 厚Al箔飞片驱动至2.48 km/s时,撞击Z-切石英试样的粒子速度为1.27 km/s,与Hugoniot理论计算结果相符,表明该测试技术是可靠、有效的;多层薄膜靶结构设计（基底/烧蚀层/硅油/Al箔）可提升激光与靶物质的能量耦合效率,使飞片保持更好的宏观完整性。为开展超短脉冲激光加载下材料动态特性研究提供了一种有效的技术途径。     

频移分离型三维激光多普勒测速仪研究

研究一种采用频移分离方法的新型三维激光多普勒测速仪（３ＤＬＤＶ）。该仪器以单色Ｈｅ－Ｎｅ激光器和单只光电探测器并配合简单的光学发射和接收系统即实现了三维速度分量的同时测量。三个分量的速度信号由声光调制器引入的三种光学频移区分，通过电子滤波器完成信号的相互分离。在光学发射系统设计中采用独特的单轴四光束结构，通过光束组合形成三双光束差动模式的激光多普勒测速仪光。本文中还给出了该仪器的系统设计参数并分析     

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.     

Research on beamforming method for dual-line array with space mismatch between the two line arrays

The performance of port/starboard discrimination of dual-line array will be seriously degraded when the space between the two line arrays of the dual-line array is mismatched. The directivity function of the delay-sum and delay-subtract beamforming is deduced and the port/starboard discrimination of the delay-sum and delay-subtract beamforming is also studied both under the ideal status and the status under which the space between the two line arrays of the dual-line array is mismatched. Analysis results show the delay-subtract beamforming has better performance of port/starboard discrimination. At last, the sea trial results demonstrate the theoretical results.     

Retrieval of ultraviolet skylight radiances and O3 slant column densities from balloon-borne limb spectrometer

With a novel light-weight and absolutely calibrated ultraviolet （UV） spectrometer, UV skylight radiances and O3 slant column densities are measured by balloon-borne limb measurements in Xinjiang area, China. UV skylight radiances measured at the height of 31 km are compared with the results from Modtran in the wavelength range from 290 to 420 nm. O3 slant column densities are derived from radiance spectra in the Huggins bands （320 - 335 nm） using differential optical absorption spectroscopy method. And the parameter exhibits a good correlation with the same value simulated by radiative transfer model （Tracy）. The O3 profile simultaneously measured by an O3 sonde is used as input in Tracy calculations. The O3 sonde is launched on the same balloon.     

Design optimization of highly sensitive LSPR enhanced surface plasmon resonance biosensors with nanoholes

For breaking through the sensitivity limitation of conventional surface plasmon resonance (SPR) biosensors, novel highly sensitive SPR biosensors with Au nanoparticles and nanogratings enhancement have been proposed recently.But in practice, these structures have obvious disadvantages.In this study, a nanohole based sensitivity enhancement SPR biosensor is proposed and the influence of different structural parameters on the performance is investigated by using rigorous coupled wave analysis (RCWA).Electromagnetic field distributions around the nanohole are also given out to directly explain the performance difference for various structural parameters.The results indicate that significant sensitivity increase is associated with localized surface plasmons (LSPs) excitation mediated by nanoholes.Except to outcome the weakness of other LSP based biosensors, larger resonance angle shift, reflectance amplitude, and sharper SPR curves' width are obtained simultaneously under optimized structural parameters.     

Polymer gratings based on photopolymerization for low-order distributed feedback polymer lasers

Novel polymer distributed feedback(DFB)gratings are fabricated based on photopolymerization to reduce lasing threshold of polymer lasers.A photopolymer formulation sensitive to 355-nm ultraviolet(UV)light is proposed for the fabrication of polymer gratings and it can be used to form polymer films by spin-coating process.A very low surface-relief depth ranging from 12.5 to about 1.0 nm has been demonstrated with a refractive-index modulation of about 0.012.The experimental results indicate that such polymer gratings have promising potentials for the fabrication of low-order DFB organic semiconductor lasers.     

A novel methodology for photometric compensation of projection display on patterned screen

We propose a novel methodology based on the projector-camera (ProCam) system to address the photometric compensation issue for the projection display on the patterned screen.The patterned screen is treated as the combination of a perfect white screen and a color modulator.The perfect white screen is used to automatically and accurately characterize the ProCam system offline using the polynomial model,and the parameters of the color modulator can be efficiently recovered by employing only two gray images based on the linear reflectance model.The experimental results show that the color artifacts of the display image can be greatly improved with this methodology,which demonstrates its feasibility and validity in the photometric compensation.     

Direction-of-arrival estimation using matrix spatial prefiltering approach

An approach to direction-of-arrival （DOA） estimation for multiple narrowband farfield signals is proposed. The technique uses a novel matrix spatial prefiltering approach. Specifically, a matrix filter is designed to spatially filter the incoming data snapshots. The un-wanted components arriving from the stopband angular sectors are attenuated and the desired components from the angular sector of interest pass with minimal distortion. The matrix filter spatially filters the element-space data and the output reserves the element-space data property, which makes it very useful by passing sensor data through a spatial prefilter prior to applying many other array processors to attenuate interferences and improve system performance. Several examples of DOA estimation problem are presented to illustrate the performance of the proposed spatial prefiltering approach. Results of simulation and real data show that the pre-filter can efficiently attenuate the spatial interferences and significantly improve the estimation and resolution capability of DOA estimators at low signal-to-noise ratios for the sources located inside the passband sector. In addition, the use of spatial prefilter makes it possible to estimate DOAs for multiple sources more than the number of the elements of an array.     

Quantum efficiency calibration of opto-electronic detector by means of correlated photons method

A new calibration method of detectors can be realized by using correlated photons generated in spontaneous parametric down-conversion (SPDC) effect of nonlinear crystal.An absolute calibration system of detector quantum efficiency is performed.And its principle and experimental setup are introduced.A continuouswave (CW) ultraviolet (351 nm),diode-pumped,frequency-doubled,and solid-state laser is used to pump BBO crystal.The quantum efficiencies of the photomultiplier at 633,702,and 789 nm are measured respectively.The coincidence peaks are observed using coincidence circuit.Some measurement factors including the filter bandwidth of trigger channel,the detector position alignment and polarization of the pump light are analyzed.The uncertainties of this calibration method are also analyzed,and the relative uncertainties of total calibration are less than 5.8%.The accuracy of this method could be improved in the future.