Cryogenic to high temperature measurements in gas flows by femtosecond laser-induced CN luminescence

Temperature is a crucial parameter of gas flow fields. Here, we present a novel thermometry technique for gas flow based on femtosecond laser-induced cyano (CN) luminescence. Specifically, a femtosecond laser with a central wavelength of 267 nm is used to induce CN violet emissions in a nitrogen flow seeded with a trace amount of methane. The spectral peak of CN B²Σ⁺- X²Σ⁺ (0,0) transitions shift to longer wavelengths with increasing temperatures, and the concentration of methane does not influence this spectral shift. The calibration curve of the spectral peak position and the temperature ranging from 93 to 1028 K is obtained through the experiment, and the curve exhibits a nearly linear trend in the low-temperature regime, and an uncertainty of 3.6 % at 173 K is obtained. The technique's wide temperature measurement capability makes it suitable for gas flow temperature measurements, particularly in environments with significant temperature variations, such as wind tunnels.