斯托克斯光种子法固体相干反斯托克斯拉曼频移器的理论研究

以波动方程和受激拉曼散射(SRS)物质方程为基础,采用光种子法,建立了固体相干反斯托克斯拉曼频移器的归一化耦合波方程,研究了晶体中反斯托克斯光转换效率。在脉冲抽运条件下分析了归一化增益系数G、归一化相位失配系数ΔK以及一阶斯托克斯光种子的归一化光场振幅ψs0三个变量对固体相干反斯托克斯拉曼频移器的影响,并作出了一系列相应曲线,由所得曲线估算了各归一化变量的合理取值范围。分析结果表明,在ΔK=0时,通过增大sψ0来打破拉曼增益抑制的影响,其转换效率峰值可达到44%。而当sψ0较弱时,可选取合适的相位失配系数,反斯托克斯光转换效率可达40%。     

Optical fiber distributed temperature sensor using short term Fourier transform based simplified signal processing of Raman signals

A simplified technique using short term Fourier transform to reduce the errors in distributed temperature measurement with a Raman scattering based optical fiber sensor system is presented. The two main sources of errors are differential attenuation to anti-Stokes and Stokes signal by fiber and local change in Stokes due to change in temperature. The proposed technique compensates these errors and extracts correct temperature profile in spite of practical difficulties encountered in applying the theoretical concept. Moreover proposed technique is less complex, self-reliant, can tolerate variation in laser power, requires less dead zone and suits automation using embedded solution. Results of measurement carried out, using the system developed at RRCAT, Indore, for two hot zones having spatial width of 1.9 m (kept at 56 °C) and 1.5 m (kept at 78 °C), located at 47 m and 85 m respectively, show that these parameters can be recovered with significantly small errors.     

Recent advances in coherent anti-Stokes Raman scattering spectroscopy: Fundamental developments and applications in reacting flows

Coherent anti-Stokes Raman scattering (CARS) spectroscopy is widely used for measuring temperature and species concentration in reacting flows. This paper reviews the advances made over the last twelve years in the development and application of CARS spectroscopy in gas-phase reacting flows. The advent of high-power nanosecond (ns) lasers and off-the-shelf compact picosecond (ps) and femtosecond (fs) lasers is enabling the rapid expansion of the application of single-shot or high-bandwidth CARS spectroscopy in a way that would have been quite unimaginable two decades ago. Furthermore, compact ps lasers are paving the way for the development of a fiber-based CARS system for use in harsh environments. The objective of this paper is to provide an overview of recent progresses in ns-, ps-, and fs-CARS spectroscopy for gas-phase thermometry and species-concentration measurements since the second edition of A.C. Eckbreth's book entitled Laser Diagnostics for Combustion Temperature and Species, which was published in 1996. During the last two decades, four encompassing issues have driven the fundamental development and application of CARS spectroscopy in reacting flows: 1) measurement of temperature and concentration of multiple species with one CARS system, 2) extension of the application of traditional ns-CARS to challenging reacting flow environments, 3) performance of nonresonant background-free and collision-free measurements in high-pressure reacting flows, and 4) measurement of temperature and species concentration at high bandwidth, typically 1 kHz or greater, to address the instability and transient phenomena associated with turbulent reacting flows in the combustors and augmentors of modern propulsion systems. This review is focused on identifying and discussing the recent results of gas-phase CARS spectroscopy related to the four issues mentioned above. The feasibility of performing high-bandwidth CARS spectroscopy with one laser beam as well as the potential of tailored fs lasers for thermometry and species-concentration measurements in gas-phase reacting flows are also discussed.     

基于拉曼散射原理的分布式光纤测温系统研究

在研究拉曼散射原理及其应用技术的基础上,开发了一种分布式结构的光纤测温系统。通过对光纤的拉曼散射光谱信息进行解调处理,实现了全光纤的分布式温度检测。系统达到的温度分辨率为0.3℃,空间分辨率为3m,最大测量距离为6 000m。相关的实验室和野外试验结果表明,该系统的主要性能指标能够满足实际工程的使用要求。     

Chemically specific imaging of cryptosporidium oocysts using coherent anti-Stokes Raman scattering (CARS) microscopy

We demonstrate the application of coherent anti-Stokes Raman scattering microscopy for the rapid, label-free chemical imaging of waterborne pathogens. Chemically selective images of cryptosporidium were acquired in just a few seconds using coherent anti-Stokes Raman scattering microscopy, demonstrating its capability for the rapid detection of cryptosporidium at the single oocyst level. We discuss the applicability of such a technique in a near-real time automated water testing system.     

用于去除非共振背景的圆偏振宽带CARS光谱研究

相干反斯托克斯拉曼散射(CARS)是一种受激拉曼现象,在显微成像时,存在非共振背景,会导致光谱产生峰位偏移和谱线变形。本文利用飞秒激光作为光源,通过光栅滤波系统产生窄带泵浦光,飞秒激光激发光子晶体光纤产生超连续谱作为斯托克斯光,两束光被调制为圆偏振光后同时激发样品产生CARS光谱。通过模拟计算说明圆偏振光可以有效去除各向异性材料CARS光谱中的非共振背景,从而使CARS光谱具有和自发拉曼相似的谱线形状。聚苯乙烯微球和液晶样品的CARS光谱实验结果与模拟计算基本相符,说明圆偏振是一种有效去除CARS光谱非共振背景的方法。     

用位相失匹配CARS方法研究尿嘧啶核苷分子的振动结构

在９００～１５００ｃｍ－１波段范围内，检测了尿嘧啶核苷水溶液的ＣＡＲＳ谱。由于采用了位相失匹配方法，从而消除了非共振背景，由此确定了碱基环骨架振动的若干模式，以及Ｃ—Ｈ键和Ｎ—Ｈ键的弯曲振动模式，侧链糖环的弱振动模式也可以在谱中观察到。对失匹配方法的原理及其实验条件给予了讨论。     

环形泵相位匹配CARS技术的匹配方式和空间分辨率的实验研究

通过对环形泵辅相位匹配方式的解剖，发现所得到的CARS信号是由多种相让匹配方式产生的，分析了各种匹配方式产生的CARS强度的份额与空间分布。通过光路设计可得到与交叉BOXCARS相比拟的空间分辨率。计算和实验都证实了两束泵浦光与斯托克斯光在透镜表面上的张角有一最佳值，这种相位匹配方式是不存在相位失配的BOXCARS，并充分利用了环形泵浦束的能量。     

反斯托克斯荧光制冷及其在空间遥感领域的应用

激光诱导反斯托克斯荧光制冷，是近年来刚刚起步的一个全新的制冷概念．它在体积、重量、振动、电磁、寿命等方面都具有其他制冷方式所无法比拟的优点，针对空间红外探测器致冷苛刻的空间环境具有良好的适应性．详细介绍了反斯托克斯荧光制冷目前发展的状况，展望了它在空间遥感领域的应用前景．     

A practical-use hydrogen gas leak detector using CARS

The purpose of this research is to develop a non-contact, fast response, practical-use hydrogen gas leak detector using Coherent Anti-Stokes Raman Spectroscopy (CARS). To make it realize, the optimization of its practical light source was investigated minutely for this detector. The light source condition to generate the highest Anti-Stokes Raman light is obvious on the theory, while it is not matched with its practical condition under the physical constraints. In this study, the light source configuration was devised in which the laser beam (355 nm) is split into two optical paths and the Raman cell filled hydrogen gas is arranged on the one side. As a result, it was found that when its irradiation ratio (R = Stokes light/Pump light) was 0.140 ≤ R ≤ 0.173, the generation efficiency of the anti-Stokes light was high. The high generation efficiency of anti-Stokes light can be maintained even if the laser light intensity and hydrogen pressure to the Raman cell are changed. We discussed the difference between the obtained experimental results and the theoretical results. The detection limit of hydrogen gas concentration of our detector was set to 500 ppm. As a result, hydrogen gas up to 200 ppm ± 15% (lower detection limit: 157 ppm) could be measured. In addition, the measurement value of the hydrogen gas leaking from a nozzle was considered under the acceptance situation, too.