Study on the mid infrared emission spectral characteristics of high enthalpy air plasma jet

Abstract

Mid infrared time-resolved emission spectra of high enthalpy air plasma jet are recorded. These spectra constitute the first study of high enthalpy air plasma jet spectra in the mid infrared range. We use inductive coupling to ionize air and generate high enthalpy air plasma jets, the infrared Fourier spectrometer focuses on the plasma jet, the detection direction is perpendicular to the direction of the plasma jet, and the mid infrared plasma spectrum under medium pressure background is detected in the range of 2–$16\mu m$. Despite the arrangement of an optical detection environment, there is still a strong background in the spectrum, on which a wide and complex emission range is superimposed. Therefore, we smoothed and corrected the detection spectrum. According to NIST’s atomic spectroscopy data, it can be concluded that atoms and ions in air plasma jets are very weak in this spectral region, and the width of the mid infrared range supports molecular origin. Therefore, the molecular emission spectra are calculated, and the emission ranges are compared with the radiation characteristics of ${\mathrm{CO}}_2$ and $H_{2}O$ molecules to obtain a general understanding of the detection spectral lines. On this basis, we also study the variation of spectral intensity with voltage, plasma thickness, gas pressure, and along the direction of plasma flow in the spectral region. The study find that the main characteristic peak of ${\mathrm{CO}}_2$ is more sensitive to voltage, while the main characteristic peak of $H_{2}O$ is more sensitive to gas pressure. The research results can provide support for accurate surface temperature measurement of plasma coated targets.