Time-resolved diagnostic measurements of sub-atmospheric laser-induced air plasmas using the OI 777 nm emission

Abstract

Stark broadening of spectral lines in laser-produced plasmas is highly sensitive to changes in ambient pressure. This paper presents a novel time-resolved Stark broadening measurements of the O I emission at 777 nm in air plasmas from atmospheric pressure down to 200 Torr. The electron density is calculated from the measured Stark width, varying between 0.11-1.87×1017 m−3; the data demonstrate that decreasing ambient pressure directly decreases the electron density at a given gate delay. N II emissions are used to determine electron temperature via the Boltzmann method, which is found to range from 1.6-3 eV. The calculated temperature is higher in lower pressure air plasmas due to the absence of collisional cooling effects. The tabulated Stark broadening measurements of the O I 777 nm line will be of great use in further studies performing diagnostic calculations in low-pressure, high-temperature environments, such as high-speed aerodynamic flows.