Imaging properties of coherent anti-Stokes Raman scattering microscope

The coherent anti-Stokes Raman scattering (CARS) microscope with the combination of confocal and CARS techniques is a remarkable alternative for imaging chemical or biological specimens that neither fluoresce nor tolerate labelling. CARS is a nonlinear optical process, the imaging properties of CARS microscopy will be very different from the conventional confocal microscope. In this paper, the intensity distribution and the polarization property of the optical field near the focus was calculated. By using the Green function, the precise analytic solution to the wave equation of a Hertzian dipole source was obtained. We found that the intensity distributions vary considerably with the different experimental configurations and the different specimen shapes. So the conventional description of microscope (e.g. the point spread function) will fail to describe the imaging properties of the CARS microscope.

The intensity distributions of collected signals in coherent anti-Stokes Raman scattering microscopy

Coherent anti-Stokes Raman scattering (CARS) microscopy with the combining of confocal and CARS techniques is a remarkable alternative for imaging chemical or biological specimens that neither fluoresce nor tolerate labeling. The CARS is a nonlinear optical process, the imaging properties of CARS microscopy will be very different from the conventional confocal microscopy. In this paper, we calculated the propagation of CARS signals by using the wave equation in medium and the slowly varying envelope approximation (SVEA), and find that the intensity angular distributions vary considerably with the different experimental configurations and the different specimen shapes. So the conventional description of microscopy (e.g.. the point spread function) will fail to descript the imaging properties of CARS microscopy. (c) 2004 Elsevier B.V. All rights reserved.

Anti-Stokes photoluminescence in ZnO microcrystal

Low temperature (10 K) strong anti-Stokes photoluminescence (ASPL) of ZnO microcrystal excited by low power cw 532 nm laser is reported here. Energy upconversion of 1.1 eV is obtained in our experiment with no conventional nonlinear effect. Through the study of the normal photoluminescence and temperature dependence of ASPL we conclude that the green band luminescence in ZnO is related to deep donor to valance band transition. Using the two-step two-photon absorption model, we provide a plausible mechanism leading to the ASPL phenomenon in our experiment. (c) 2006 American Institute of Physics.

Multiplex CARS measurements in supersonic H-2/air combustion

H-2 and O-2 multiplex coherent anti-stokes Raman spectroscopy (CARS) employing a single dye laser has been explored to simultaneously determine the temperature and concentrations of H-2 and O-2 in a hydrogen-fueled supersonic combustor. Systematic calibrations were performed through a well-characterized H-2/air premixed flat-flame burner. In particular, temperature measurement was accomplished using the intensity ratio of the H-2 S(5) and S(6) rotational lines, whereas extraction of the H-2 and O-2 concentrations was obtained from the H-2 S(6) and O-2 Q-branch, respectively. Details of the calibration procedure and data reduction are discussed. Quantification of the supersonic mixing and combustion characteristics applying the present technique has been demonstrated to be feasible. The associated detection limits as well as possible improvements are also identified.

探测气体平衡及非平衡态的相干反斯托克斯喇曼散射技术

<正> 一、引言 这篇综述的目的在于介绍最近发展起来的相干反斯托克斯喇曼散射(Coherent Anti-Stokes Raman Scattering(CARS))方法在诊断平衡及非平衡态气体中的应用,包括实验及理论两部分.文内还扼要介绍了我们正在筹备的测试系统的方案。 在气体中,特别在稀薄气体非平衡流动中,探测粒子数密度分布;混合含气中各组分,各能态的分布;平动、振动、转动温度;粒子的激发和弛豫过程,都是比较困难的,而这些

Accurate determination of electronic transition energy of carbon nanotubes from the resonant behavior of radial breathing modes and their overtones

The resonant Raman behavior of the radial breathing modes are very useful to analyze the electronic property of carbon nanotubes. We investigated the resonant behaviors of Stokes and anti-Stokes radial breathing mode and its overtone of a metallic nanotube, and show how to accurately determine the electronic transition energy of carbon nanotubes from radial breathing modes and their overtones. Based on the present results, the previously reported resonant Raman behavior of the radial breathing modes of SWINT bundles can be interpreted very well.

Observation of the resonant Raman behavior of individual single-walled carbon nanotubes

The different resonant Raman scattering process of single-walled carbon nanotubes (SWNTs) has been found between the Stokes and anti-Stokes sides of the radial breathing modes (RBMs), and this provides strong evidence that Raman spectra of some special diametric SWNTs are in resonance with their electronic transitions between the singularities in the one-dimensional electronic density of states in the valence and conduction bands, and other SWNTs axe beyond the resonant condition. Because of the coexistence of resonant and non-resonant Raman scattering processes for different diametric SWNTs, the relative intensity of each RBM does not reflect the proportion of a particular SWNT.

相干反-斯托克斯喇曼光谱术

相干反斯托克斯喇曼光谱(Coherent Anti-Stokes Raman Spectra,简称CARS)是一种非线性光学混频过程。同时使用两条入射激光束聚焦于样品,输出相当于反-斯托克斯频率光束。量子效率可达1%,散射强度比自发喇曼谱高10~5倍以上,连续CARS谱分辩率为0.01cm~(-1)。这种具有高空间分辩、高抗荧光干扰、高分辩率及高效率等特点的CARS技术,

Numerical solution of the incompressible Navier-Stokes equations with an upwind compact difference scheme

A new finite difference method for the discretization of the incompressible Navier-Stokes equations is presented. The scheme is constructed on a staggered-mesh grid system. The convection terms are discretized with a fifth-order-accurate upwind compact difference approximation, the viscous terms are discretized with a sixth-order symmetrical compact difference approximation, the continuity equation and the pressure gradient in the momentum equations are discretized with a fourth-order difference approximation on a cell-centered mesh. Time advancement uses a three-stage Runge-Kutta method. The Poisson equation for computing the pressure is solved with preconditioning. Accuracy analysis shows that the new method has high resolving efficiency. Validation of the method by computation of Taylor's vortex array is presented.

Perturbational Finite Volume Method For The Solution of 2-D Navier-Stokes Equations on Unstructured and Structured Colocated Meshes

Based on the first-order upwind and second-order central type of finite volume( UFV and CFV) scheme, upwind and central type of perturbation finite volume ( UPFV and CPFV) schemes of the Navier-Stokes equations were developed. In PFV method, the mass fluxes of across the cell faces of the control volume (CV) were expanded into power series of the grid spacing and the coefficients of the power series were determined by means of the conservation equation itself. The UPFV and CPFV scheme respectively uses the same nodes and expressions as those of the normal first-order upwind and second-order central scheme, which is apt to programming. The results of numerical experiments about the flow in a lid-driven cavity and the problem of transport of a scalar quantity in a known velocity field show that compared to the first-order UFV and second-order CFV schemes, upwind PFV scheme is higher accuracy and resolution, especially better robustness. The numerical computation to flow in a lid-driven cavity shows that the under-relaxation factor can be arbitrarily selected ranging from 0.3 to 0. 8 and convergence perform excellent with Reynolds number variation from 102 to 104.

Simulation of Free-Surface Flow in a Tank Using the Navier-Stokes Model and Unstructured Finite Volume Method

Modelling free-surface flow has very important applications in many engineering areas such as oil transportation and offshore structures. Current research focuses on the modelling of free surface flow in a tank by solving the Navier-Stokes equation. An unstructured finite volume method is used to discretize the governing equations. The free surface is tracked by dynamically adapting the mesh and making it always surface conforming. A mesh-smoothing scheme based on the spring analogy is also implemented to ensure mesh quality throughout the computaiton. Studies are performed on the sloshing response of a liquid in an elastic container subjected to various excitation frequencies. Further investigations are also carried out on the critical frequency that leads to large deformation of the tank walls. Another numerical simulation involves the free-surface flow past as submerged obstacle placed in the tank to show the flow separation and vortices. All these cases demonstrate the capability of this numerical method in modelling complicated practical problems.

扩散抛物化Navier-Stokes方程数值解法评述

20世纪60年代末期在边界层理论基础上发展起来的各种简化Navier-Stokes(N-S)方程(统称为扩散抛物化N-S方程)及其算法,较为彻底地解决了无黏流及黏流的相互干扰问题,并为高雷诺数大型复杂黏性流场的数值模拟开辟了新的途径.本文将系统地评述这一领域的主要成果,包括各种简化N-S模型的优缺点;数学奇性及正则化方法;代表性的数值解法以及最近几年的新进展.

Navier-Stokes方程二阶速度滑移边界条件的检验

对微尺度气体流动，Navier-Stokes方程和一阶速度滑移边界条件的结果与实验数据相比，在滑移区相互符合，在过渡领域则显著偏离，为改善Navier-Stokes方程在过渡领域的表现，有些研究者尝试引入二阶速度滑移边界条件，如Cercignani模型，Deissler模型和Beskok-Karniadakis模型．以微槽道气体流动为例，将Navier-Stokes方程在不同的二阶速度滑移模型下的结果与动理论的直接模拟Monte Carlo（DSMC）方法和信息保存（IP）方法以及实验数据进行比较．在所考察的3种具有代表性的二阶速度滑移模型中，Cercignani模型表现最好，其所给出的质量流率在Knudsen数为0．4时仍与DSMC和IP结果相符；然而，细致比较表明，Cercignani模型给出的物面滑移速度及其附近的速度分布在滑流区和过渡领域的分界处（Kn=0．1）已明显偏离DSMC和IP的结果．

高雷诺数流动的控制方程体系和扩散抛物化Navier-Stokes方程组的意义和用途

在计算机发达的时代,高雷诺(Re)数绕流计算中有无必要使用简化NS方程组,本文讨论这个问题.主要内容如下:(1)高Re数绕流包含3种基本流动:所有方向对流占优流动、所有方向对流扩散竞争流动和部分方向对流占优部分方向对流扩散竞争流动(简称干扰剪切流动),3个基本流动的特征彼此不同且在流场中所占领域大小彼此相差悬殊,NS方程区域很小,它们的最简单控制方程组Euler、Navier-Stokes(NS)和扩散抛物化(DP)NS方程组的数学性质彼此不同,因此利用Euler-DPNS-NS方程组体系分析计算高Re数绕流流动就是一个合乎逻辑的选择,该法与利用单一NS方程组的常用方法可以彼此检验和补充.(2)流体之间以及流体与外界的动量、能量和质量交换,流态从层流到湍流的演化主要发生在干扰剪切流动中,干扰剪切流及其最简单控制方程--DPNS方程组具有基础意义;DPNS方程组笔者在1967年已提出.(3)诸简化NS方程组:DPNS、抛物化(P)NS、薄层(TL)NS、黏性层(VL)NS方程组的发展、相互关系,它们的历史贡献和今后的用途;它们的数学性质均为扩散抛物型,但它们包含的黏性项彼此有所不同;从流体力学角度来看,它们中只有DPNS方程组能够准确描述干扰剪切流动.提出把诸简化NS方程组统一为DPNS方程组的建议.(4)干扰剪切流--DPNS方程组与无干扰剪切流--边界层方程组之间的关系以及进一步研究干扰剪切流的意义.