Femtosecond Coherent Anti-Stokes Raman Scattering for Time-Resolved Measurements of Temperature and Species Concentrations in Flames

项目简介:飞秒相干反斯托克斯拉曼散射用于火焰温度和物质浓度的时间分辨测量[j]提出的工作的主要目标是开发和应用基于超快激光的相干反斯托克斯拉曼散射（CARS）技术，用于以1khz或更高的数据速率单次测量温度和物质浓度。从湍流介质中获得完全时间分辨的数据将为湍流火焰模型提供更严格和有意义的测试，最终导致燃烧器效率更高，污染物排放水平更低。在实际燃烧器的测试过程中，测量的1 khz数据速率将是一个很大的优势，特别是当测试持续时间受到设备考虑的限制时。这项工作代表了将飞秒汽车传感器用于能源和环境应用的第一步。本研究将为机械工程专业的研究生提供良好的训练。飞秒（fsec） CARS项目将为机械工程研究生提供许多多学科活动的机会，因为fsec激光系统的操作需要光学物理学和电子学方面的专业知识。fsec激光系统和fsec激光物理的主题将被纳入高级激光诊断的研究生课程。本研究将积极招募来自代表性不足群体的本科生和研究生。为了协助本科生和研究生的招聘，将建立一个fsec CARS项目网站。飞秒CARS测量将使用普渡大学现有的激光设备进行；可以产生标称脉冲长度为80 fsec的780nm激光脉冲，脉冲能量超过1mj，重复频率为1khz。泵浦脉冲和探测脉冲将使用光参量放大器产生。为了以1khz或更高的数据速率测量温度和/或物质浓度，将使用脉冲长度为2-3 psec的啁啾脉冲探测光束将拉曼相干的时间行为映射到CARS信号的频谱上。CARS信号将使用光谱仪进行分散，并使用背照电子倍增CCD （EMCCD）进行检测。该EMCCD相机已被开发为帧传输相机，CARS光谱可以在1 kHz或更高的数据速率下提取。计算fsec CARS信号生成过程的独特数值方法将用于探索fsec CARS过程的物理特性，包括泵浦和斯托克斯光束相互作用以产生拉曼相干性的细节，并开发用于从实验数据确定温度和物种浓度的计算机代码。

PROJECT ABSTRACT: Femtosecond Coherent Anti-Stokes Raman Scattering for Time-Resolved Measurements of Temperature and Species Concentration in FlamesRobert P. Lucht and Xianfan Xu School of Mechanical Engineering, Purdue University, W. Lafayette, IN 47907-2088The primary objective of the proposed work is the development and application of ultrafast-laser-based coherent anti-Stokes Raman scattering (CARS) techniques for single-shot measurements of temperature and species concentrations at data rates of 1 kHz or greater. The acquisition of fully time-resolved data from turbulent media will provide more rigorous and meaningful tests of turbulent flame models, leading eventually to combustors that are more efficient and have lower levels of pollutant emission. The 1-kHz data rate of the measurements will be a great advantage during testing of practical combustors, especially when the test duration is limited by facility considerations. The work represents a first step toward enabling femtosecond CARS based sensors for energy and environment applications. The proposed research will provide excellent training for graduate students in mechanical engineering. The femtosecond (fsec) CARS project will provide numerous opportunities for multidisciplinary activities for mechanical engineering graduate students, because operation of the fsec laser systems requires considerable expertise in optical physics and electronics. The subjects of fsec laser systems and fsec laser physics will be incorporated in a graduate class on advanced laser diagnostics. Students from underrepresented groups will be actively recruited for this research, at both the undergraduate and graduate levels. To assist in undergraduate and graduate recruitment, a fsec CARS project web site will be created. The femtosecond CARS measurements will be performed using an existing laser facility at Purdue University; laser pulses at 780 nm with a nominal pulse length of 80 fsec can be generated with pulse energies in excess of 1 mJ at a repetition rate of 1 kHz. Pump and probe pulses will be produced using an optical parametric amplifier. To measure temperature and/or species concentrations at data rates of 1 kHz or greater, a chirped-pulse probe beam with a pulse length of 2-3 psec will be used to map the temporal behavior of the Raman coherence onto the frequency spectrum of the CARS signal. The CARS signal will be dispersed using a spectrometer and detected using a back-illuminated electron multiplying CCD (EMCCD). This EMCCD camera has been developed as a frame transfer camera and CARS spectra can be extracted at data rates of 1 kHz or greater. Unique numerical methods for calculation of the fsec CARS signal generation process will be used to both explore the physics of the fsec CARS process, including the details of the interaction of the pump and Stokes beams to create the Raman coherence, and to develop computer codes for determination of temperatures and species concentrations from experimental data.