Numerical study of collisional effects in saturated absorption spectrum of argon arcjet plasma

Abstract

We numerically studied the saturated absorption spectrum of an argon arcjet plasma with the aim of developing a method for diagnosing the collision parameters of the plasma. In a plasma with strong velocity-changing collisions with a buffer gas, the saturated absorption spectrum was partially or fully broadened to a Gaussian shape whose width is on the same order as that of the Doppler broadening. In an argon arcjet plasma—a plasma that exhibits an intermediate pressure region, a variety of saturated absorption spectra have been experimentally observed by tuning the pressure in the discharge section. We performed a numerical analysis to validate the shape of the experimentally observed spectrum by numerically solving the two-state rate equation system with the assumption of strong velocity-changing collisions. In particular, we numerically reproduced the spectrum with an inverted pedestal, which has not been previously reported, by assuming that the collisional frequency is significantly different for each electronic state. The conditions for the emergence of the inverted pedestal were numerically determined by regression.