Spectral Property Investigation of Air Plasma Generated by Pulsed $\hbox {CO}_{2}$ Laser

In this paper, the laser propulsion plasma has been diagnosed experimentally using the method of optical emission spectroscopy. The spectral evolution of the air plasma generated by pulsed CO₂ laser radiation with a parabolic reflector was studied, with a pulse energy of 2 J and a pulsewidth of 70 ns (full-width at half-maximum). In addition, most of the plasma spectral lines in the visible light region were identified, and the spectra of air plasma were dominated by the emission of single ionization of nitrogen and oxygen, with a weak emission of nitrogen and oxygen atom. Based on the local-thermodynamic-equilibrium state, the basic spectral properties of laser-induced plasma evolution, including the evolution of the plasma spectrum, electron temperature, and electron number density, were analyzed. We utilized the Boltzmann plot to evaluate the electron temperature and the Stark broadening and Stark center frequency shift to evaluate the electron number density. Results proclaimed that the maximum values of the electron temperature and electron number density were about 4.5 × 10 K and 10¹⁹ cm^-3, respectively.