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.
单 沅，严 浩，刘旭辉，韩 磊，鲁 政，刘子晗，李 博，高 强. 低压环境下飞秒激光诱导氰基化学发光特性研究[J]. 光谱学与光谱分析, 2025, 45(09): 2445-2451.
SHAN Yuan, YAN Hao, LIU Xu-hui, HAN Lei, LU Zheng, LIU Zi-han, LI Bo, GAO Qiang. Study on the Characteristics of Femtosecond Laser-Induced Cyano
Chemiluminescence Under Low-Pressure Environment. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2025, 45(09): 2445-2451.
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