Accuracy enhancement in Brillouin scattering distributed temperature sensor based on Hilbert transform

The scattering optical signal of OTDR based Brillouin scattering distributed sensor is very weak and have a frequency width of several decades megahertz, so it is hard to perform the traditional analogue coherent demodulation. A novel optical coherent detection based on Hilbert transform is presented here. In detail, Brillouin backscattering light is coherent detected with the reference light, which is modulated by microwave electric optical modulator to produce frequency-adjustable light, then the detected photocurrent signal is demodulated by digital signal processing based on Hilbert transform, and at last the distributed sensing signal with better S/N ratio is gained, which can enhance the performance of the sensor. The simulation and experimental results of the detection method are given.     

Spatial and temporal distortions of a signal during multiple scattering

A calculation procedure is described which can be used to determine the spatial and temporal distortions of a signal at the receiver input for any angular characteristic of the radiation source, receiver directional pattern, or scattering characteristic of the medium. This procedure can be used to determine the signal envelope at the receiver input with respect to time and angular coordinates. The procedure is based on a study of the solution of the nonsteady-state radiation-transport equation. An expression is given for the k-th scattering order.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 12, No. 6, pp. 70–73, June, 1969.     

Achievement of Narrow-Band CARS Signal by Manipulating Broad-band Laser Spectrum

We theoretically demonstrate the achievement of narrow-band coherent anti-Stokes Raman scattering （CARS） signal by manipulating broad-band probe spectrum. The narrowing of the CARS signal depends on the spectrum bandwidth of the probe beam, and thus high-resolution CARS signal for a complicated quantum system can be obtained by the simple spectrum manipulation. Furthermore, the energy-level diagram for the complicated quantum system can also be labelled by measuring the CARS signal at a given frequency.     

Lidar observation of the bubble trace in the sea surface layer

The evolutions of the signals of the elastic (Mie) and Raman backscattering of the Nd:YAG laser second-harmonic radiation in the upper layer of the sea under cavitational perturbation induced by the passage of a high-speed boat are compared under the conditions of the outdoor experiment. It is shown that the signal of the elastic scattering on bubbles returns to the background level within the time of ∼10 min. The relaxation time of the spontaneous Raman scattering signal can be an order of magnitude larger than this value (the evaluated value under the particular conditions of this experiment is ∼120 min). Interpretation is given to this difference in attenuation time of the elastic and inelastic scattering signals at the cavitational perturbation of the sea.     

Hyper-Raman scattering from vitreous boron oxide: coherent enhancement of the boson peak

Hyper-Raman scattering spectra of vitreous B(2)O(3) are compared to Raman scattering ones. Particular attention is given to the low-frequency boson peak which relates to out-of-plane rigid librations of planar structural units, mostly boroxols. While the Raman strength can be accounted for by the motions of single units, the hyper-Raman signal exhibits a unequaled enhancement due to coherent librations of several boroxols. This important distinction is explained by the different symmetry properties of the polarizability and hyperpolarizability tensors of the structural units.     

Pulse-shape distortion in transmission experiments with incoherent phonons in isotropic solids due to elastic scattering

Assuming homogeneously distributed elastic scattering centers in an isotropic dielectric plate, the transmission and distortion of phonon pulses, that are transmitted from a radiator element to a centered detector element at the opposite face, are investigated theoretically. Analytic expressions are derived for the singlescattered phonon signal due to three different phenomenological scattering characteristics: isotropic scattering, preferential forward scattering, and preferential forward/backward scattering. In particular, we find that the asymptotic decay of the scattered phonon signal depends on the associated scattering characteristic. Numerical results are given for the excitation by a delta pulse using all three scattering characteristics. As a special case, the pulse-shape distortion of a rectangular pulse of 100 ns duration is treated in more detail. Parameter is the ratio of phonon mean free path to plate thickness.     

Femtoscopy within a hydrodynamic approach based on flux tube initial conditions

In pp scattering at LHC energies, large numbers of elementary scatterings will contribute significantly, and the corresponding high multiplicity events will be of particular interest. Elementary scatterings are parton ladders, identified with color flux tubes. In high multiplicity events, many of these flux tubes are produced in the same space region, creating high energy densities. We argue that there is good reason to employ the successful procedure used for heavy ion collisions: matter is assumed to thermalize quickly, so that the energy from the flux tubes can be taken as initial condition for a hydro-dynamic expansion. This scenario gets spectacular support from very recent results on Bose-Einstein correlations in pp scattering at 900 GeV at the LHC.     

超宽带散射信号的时域测量及处理

 叙述了在超宽带电磁脉冲照射下良导电散射体散射信号的时域测量技术及数据处理方法。描述了产生散射信号的物理过程,散射信号的时域测量步骤、提取方法以及散射体冲激响应的计算方法。通过对铝金属球体散射信号的测量及处理,说明了上述测量技术和数据处理方法是有效的,基本满足逆散射成像的要求。     

Estimation of surface roughness effect on spectral characteristics of tone signals propagating along stationary paths in a shallow sea

Scattering of a tonal low-frequency (up to 400 Hz) acoustic signal on a rough surface during its propagation along stationary paths in a shallow water area is considered. A calculation technique of estimating the spectral power density of the signal scattered at wind waves (reverberation) given an arbitrary angular distribution of the wind wave is developed based on the Bragg scattering model. The obtained results are compared with the results of numerical simulation of resonant sound scattering at surface perturbations according to an algorithm proposed by the authors, as well as with the results of experimental investigations.     

水下目标弹性声散射信号分离

水下目标弹性声散射与其他声散射成分在时域和频域上均存在混叠, 现有信号处理方法受分辨力限制无法在混叠状态下识别目标弹性声散射特征. 针对这个问题, 提出了一种目标弹性声散射信号分离方法. 以目标回波亮点模型为基础, 分析了线性调频信号入射时目标声散射成分的信号特性, 提出了一种目标声散射成分向单频信号的映射方法, 并理论推导出了目标声散射结构与映射结果之间的线性对应关系, 实现了通过窄带滤波分离出目标弹性声散射成分. 仿真与消声水池实验数据处理结果表明, 该方法基本可以完全分离出目标回波信号中的弹性声散射成分, 分离出的弹性声散射具有与理论一致的信号特征, 验证了该分离方法的有效性.     

How can the odderon be detected at RHIC and LHC?

The odderon remains an elusive object, 33 years after its invention. The odderon is now a fundamental object in QCD and it has to be found experimentally if QCD is right. In the present paper, we show how to find it at RHIC and LHC. The most spectacular signature of the odderon is the predicted difference between the differential cross-sections for proton–proton and antiproton–proton at high s and moderate t. This experiment can be done by using the STAR detector at RHIC and by combining these future data with the already present UA4/2 data. The odderon could also be found by the ATLAS experiment at LHC by performing a high-precision measurement of the real part of the hadron elastic scattering amplitude at small t.     

基于光相干外差检测的布里渊散射DOFS的研究

对布里渊散射分布式光纤传感器(DOFS)检测原理进行了分析, 针对布里渊散射光信号的特点, 应用光相干和外差技术来检测布里渊散射光信号. 具体采用微波电光调制产生频率可调的参考光, 和布里渊散射光进行相干检测, 根据布里渊频移特性取出布里渊散射光信号, 从而得到分布式传感信号. 分别实现了25 km光纤的分布式温度和应变传感, 达到3℃的温度分辨率、100 με的应变分辨率和10 m的空间分辨率.     

All-Fiber Ultra-Fast Switching Using Stimulated Raman Scattering

We propose a method for all-fiber ultra-fast switching using stimulated Raman scattering. It is based on the transference of energy from the signal as pump to the control signal as first Stokes by stimulated Raman scattering. In the absence of a control signal, the transference of energy from the pump signal to the generated first Stokes is negligible, which results in high output power at the pump signal wavelength. To minimize the walk-off problem between two wavelengths, we chose pump signal and control signal to be equally spaced on opposite sides of the zero dispersion wavelength of the fiber. Based on this assumption, the all-fiber ultra-fast optical switch with low power consumption and high output extinction ratio can be realized.     

What can we learn by comparing experimental and theoretical-computational X-ray scattering data?

In this letter we use X-ray scattering data of liquid water, as obtained by different experimental and theoretical-computational procedures, to address the problem of quantitative modeling of the scattering signal in liquids. In particular we investigate the accuracy of well optimized water models in reproducing top level X-ray experimental results and compare experimental data variations with the ones given by different theoretical-computational models. Results show that the experimental scattering data have an intrinsic noise which is comparable to the deviations of the theoretical-computational signals, hence suggesting that no reliable refinement based on scattering data is possible for such models.     

高光谱分辨率激光雷达鉴频器的设计与分析

提出了利用Fabry-Perot干涉仪的反射场实现高光谱分辨率激光雷达精细探测大气光学参量的新方法和思路.设计了高光谱分辨率的分光系统,并分析了干涉仪反射场的光谱透过特征曲线.结合高光谱激光雷达探测信号特征,讨论分析了谱分离比和瑞利信号透过率随反射率和腔长的变化曲线,同时结合误差传递公式,建立了仿真分析模型,讨论了回波光束发散角和入射角变化对激光雷达探测结果的影响.结果表明,所提出的Fabry-Perot干涉仪反射场可以实现高光谱分辨率激光雷达探测系统的精细分光,同时探测结果误差随回波光束发散角变化不敏感,控制发散角在10 mrad以内,入射角在1.5 mrad以内时,可以实现气溶胶光学参数廓线的高精度探测.     

Statistics of a coherent lidar signal in a turbulent atmosphere

Absolute and conditional statistical properties of a pulse coherent Doppler lidar signal in a turbulent atmosphere are studied. Upon coherent receiving of optical fields scattered by a large number of particles, the lidar signal is shown to be a nonstationary non-Gaussian random process with Gaussian conditional statistical characteristics. The appearance of non-Gaussian properties of the signal is caused by correlation of turbulent fluctuations of the wind velocity field within the scattering volume. For the considered signal model, which corresponds to the single scattering approximation and is a sum of a large number of random variables, the central limit theorem is found to be untrue due to the statistical dependence of particles’ positions in a turbulent atmosphere. The results of numerical calculations show that, for a homogeneous and isotropic turbulence, the behavior of the signal statistics significantly depends on the size of the scattering volume and on the state of atmospheric turbulence. A Gaussian statistics is observed at small heights; with an increase in height, the non-Gaussian component becomes considerable in fluctuations of the lidar signal.     

Detecting submerged objects by Brillouin scattering

The principle of detecting submerged objects by Brillouin scattering is analyzed. It is based on testing the frequency shift rather than the intensity of the scattered signal. Experiments based on the principle are carried out. An actual detecting system for practical applications is designed, and the experimental results obtained by using the system are given. The experimental results show that the method of Brillouin scattering possesses several advantages compared to the method of testing the signal intensity. The conclusion is that Brillouin scattering is a good method for detecting submerged objects. PACS 42.68.Wt; 42.79.Qx; 78.35.+c     

基于自回归模型的超细颗粒动态光散射模拟

为了获取超细颗粒动态散射光模拟信号, 在分析超细颗粒动态散射光信号特性的基础上, 通过建立动态光散射随机过程的自回归(AR)模型, 利用Levison-Durbin递推算法确定模型参数, 并给出了单峰、双峰分布颗粒信号模拟的模型阶数确定方法, 从而提出了一种基于AR模型的态光散射信号模拟方法。分别对50 nm, 300 nm, 1000 nm, 50 nm与1000 nm, 100 nm与500 nm, 300 nm与1000 nm的单峰、双峰分布颗粒在模型阶数分别为1, 1, 1, 57, 28, 40时进行了模拟, 得到的模拟信号的光强自相关函数与理论值吻合, 用累积法对单峰分布颗粒反演和双指数法对双峰分布颗粒反演, 相对误差分别小于0.58%和3.7%, 因此, 单峰分布颗粒信号模拟需一阶模型, 双峰分布颗粒信号模拟粒径不同所需阶数不同。     

Multiple-scattering in radar systems: A review

Although extensively studied within the lidar community, the multiple scattering phenomenon has always been considered a rare curiosity by radar meteorologists. Up to few years ago its appearance has only been associated with two- or three-body-scattering features (e.g. hail flares and mirror images) involving highly reflective surfaces.Recent atmospheric research aimed at better understanding of the water cycle and the role played by clouds and precipitation in affecting the Earth's climate has driven the deployment of high frequency radars in space. Examples are the TRMM 13.5 GHz, the CloudSat 94 GHz, the upcoming EarthCARE 94 GHz, and the GPM dual 13-35 GHz radars. These systems are able to detect the vertical distribution of hydrometeors and thus provide crucial feedbacks for radiation and climate studies. The shift towards higher frequencies increases the sensitivity to hydrometeors, improves the spatial resolution and reduces the size and weight of the radar systems. On the other hand, higher frequency radars are affected by stronger extinction, especially in the presence of large precipitating particles (e.g. raindrops or hail particles), which may eventually drive the signal below the minimum detection threshold. In such circumstances the interpretation of the radar equation via the single scattering approximation may be problematic. Errors will be large when the radiation emitted from the radar after interacting more than once with the medium still contributes substantially to the received power. This is the case if the transport mean-free-path becomes comparable with the instrument footprint (determined by the antenna beam-width and the platform altitude).This situation resembles to what has already been experienced in lidar observations, but with a predominance of wide- versus small-angle scattering events. At millimeter wavelengths, hydrometeors diffuse radiation rather isotropically compared to the visible or near infrared region where scattering is predominantly in the forward direction. A complete understanding of radiation transport modeling and data analysis methods under wide-angle multiple scattering conditions is mandatory for a correct interpretation of echoes observed by space-borne millimeter radars.This paper reviews the status of research in this field. Different numerical techniques currently implemented to account for higher order scattering are reviewed and their weaknesses and strengths highlighted. Examples of simulated radar backscattering profiles are provided with particular emphasis given to situations in which the multiple scattering contributions become comparable or overwhelm the single scattering signal. We show evidences of multiple scattering effects from air-borne and from CloudSat observations, i.e. unique signatures which cannot be explained by single scattering theory. Ideas how to identify and tackle the multiple scattering effects are discussed. Finally perspectives and suggestions for future work are outlined.This work represents a reference-guide for studies focused at modeling the radiation transport and at interpreting data from high frequency space-borne radar systems that probe highly opaque scattering media such as thick ice clouds or precipitating clouds.     

散射介质超衍射极限技术研究进展

综述了已有散射介质超衍射极限聚焦和成像技术的研究现状及进展。首先介绍了这一领域的研究背景及意义,以及已有超衍射极限成像技术的发展现状;然后给出了应用于超衍射极限成像的散射介质定义;其次分析了时间反演技术在声学、微波领域聚焦上的应用,介绍了时间反演法在光学领域超衍射极限聚焦应用中的实现方法,总结了散射介质加入到光学系统中的作用,分析了利用反馈控制调节和光学相位共轭方法进行散射介质超衍射极限聚焦方法的特点;讨论了基于空域和空频域传输矩阵测量的散射介质宽场成像方法及在该目的下的散射介质制备方法;最后给出了散射介质光学超衍射极限成像技术研究前景及展望。