【摘要】 飞秒激光分子标记测速是目前主流的非侵入式测速技术，在常压环境下的速度场测量方面应用广泛，尤其是在超声速及高超声速流场测量方面极具优势。目前，飞秒激光分子标记测速方法主要包括标记氮气分子的飞秒激光电子激发标记测速技术和标记甲烷/氮气混合气的飞秒激光诱导氰基化学发光测速技术（FLICC）。与飞秒激光电子激发标记测速技术相比，FLICC技术的信号强度和持续时间都具有极大的优势，其测速范围和适用场景也得到了极大的拓宽。该技术可以为高速风洞、航空航天推进系统等环境下的流场速度测量提供技术支持。然而，高速流场往往伴随着低压的环境，如地面的低压风洞、近地或深空等环境。因此，研究低压环境下的流场测速技术具有重要的意义。目前，FLICC技术在低压环境下测速的适用性还无法确定。由于FLICC技术是通过拍摄发光分子在一定时间内的位移获得速度信息，因此被标记分子发光的强度和持续时间直接决定着该技术的应用可行性。在低压环境下，由于粒子数密度降低，飞秒激光与分子作用以及粒子之间的能量传递都会受到影响，进而影响发光的强度和寿命。本工作主要研究从常压到低压环境下FLICC的发光特性，实验中，低压腔压力可以在10 Pa至0.1 MPa间调节，腔内为1%浓度的CH₄/N₂混合气，飞秒激光入射到低压腔中与混合气作用，诱导化学反应生成高能态的CN,通过CN（B-X）的跃迁发出荧光，利用ICCD相机和光谱仪对光谱进行成像。通过拍摄不同时间延迟下的光谱信息，获得不同压力下CN发光谱线的强度和持续时间，建立了光谱强度随压力的变化曲线。结果表明，随着压力的降低，CN的发光强度逐渐下降，在10 Pa的压力下仍保持着较好的信号强度，通过ICCD相机的延迟成像，获得其荧光寿命约为5μs,满足FLICC的测速要求。该研究为FLICC技术在低压环境下的应用打下基础。更多还原

【Abstract】 Femtosecond laser molecular tagging velocimetry is currently the most mainstream non-intrusive velocimetric technique and is widely used in velocity field measurement in atmospheric pressure environments, especially having great advantages in supersonic and hypersonic flow field measurement. Currently, femtosecond laser molecular tagging velocimetry methods primarily include femtosecond laser electron excitation tagging velocimetry for tagging nitrogen molecules and femtosecond laser-induced cyano chemiluminescence velocimetry（FLICC） for tagging methane/nitrogen. Compared to femtosecond laser electron excitation tagging velocimetry, FLICC technology offers significant advantages in signal strength and duration, and its velocity measurement range and applicable scenarios have also been significantly expanded. This technology can provide technical support for flow velocity measurement in environments such as high-speed wind tunnels and aerospace propulsion systems. However, high-speed flow fields are often accompanied by low-pressure environments, such as those found in low-pressure wind tunnels on the ground, near-Earth, or in deep space. Therefore, it is of great significance to study flow field measurement technology in a low-pressure environment. Currently, the applicability of FLICC technology for velocity measurement in low-pressure environments remains undetermined. Since FLICC technology obtains velocity information by capturing the displacement of tagged luminescent molecules over a specific period, the intensity and duration of the tagged molecule’s luminescence directly determine the feasibility of its application. In low-pressure environments, due to the decrease in particle number density, the interaction between the femtosecond laser and molecules, as well as the energy transfer between particles, is affected, thereby altering the intensity and lifetime of luminescence. The main focus of this study is to investigate the luminescence characteristics of FLICC under atmospheric to low-pressure environments. In the experiment, the pressure in the low-pressure chamber can be adjusted between 10 Pa and 0.1 MPa, and the chamber is filled with a 1% concentration of CH₄/N₂ mixture. A femtosecondlaser is incident into the low-pressure chamber and interacts with the mixed gas, inducing a chemical reaction to generate high-energy CN. Fluorescence is emitted through the transition of CN（B-X）, and the spectrum is imaged using an ICCD camera and spectrometer. By capturing spectral information at different delays, the intensity and duration of various luminescence spectral lines of CN under different pressures are obtained, and a curve of spectral intensity versus pressure is established. The results show that as the pressure decreases, the luminescence intensity of CN gradually decreases. At the pressure of 10 Pa, it still maintains a good signal intensity. Through the delayed imaging of an ICCD camera, its fluorescence lifetime is about 5 μs, which meets the requirements of FLICC velocimetry technology. This research lays the foundation for the application of FLICC technology in low-pressure environments.更多还原