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

项目摘要：飞秒相干反斯托克斯拉曼散射用于时间分辨测量火焰中的温度和组分浓度普渡大学机械工程学院徐先帆，普渡大学，W.Lafayette，47907-2088年。拟议工作的主要目标是发展和应用基于超快激光的相干反斯托克斯拉曼散射(CARS)技术，用于在1千赫或更高的数据速率下单次测量温度和组分浓度。从湍流介质中获取完全时间分辨的数据将为湍流火焰模型提供更严格和更有意义的测试，最终导致更高效和更低水平的污染物排放的燃烧室。在实际燃烧室的测试中，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施考虑的限制时。这项工作代表着使飞秒汽车传感器能够用于能源和环境应用的第一步。拟议的研究将为机械工程研究生提供良好的培训。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相当多的光学物理和电子学专业知识。FSEC激光系统和FSEC激光物理的课程将纳入高级激光诊断学的研究生班。这项研究将积极招募来自代表性不足群体的学生，包括本科生和研究生。为了协助本科生和毕业生的招聘，将创建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；780 nm的激光脉冲标称长度为80fsec，脉冲能量超过1mJ，重复频率为1 kHz。泵浦和探测脉冲将使用光学参数放大器产生。为了在1 kHz或更高的数据速率下测量温度和/或物种浓度，将使用脉冲长度为2-3PSEC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信号将使用分光计进行分散，并使用背照式电子倍增电荷耦合器件(EMCCD)进行检测。这种EMCCD相机已经被开发为帧传输相机，并且CARS光谱可以在1 kHz或更高的数据速率下提取。用于计算FSEC CARS信号产生过程的独特的数值方法将被用于探索FSEC CARS过程的物理，包括产生拉曼相干的泵浦和斯托克斯光束的相互作用的细节，并开发用于根据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.