Study of atmospheric air AC glow discharge using optical emission spectroscopy and near infrared diode laser cavity ringdown spectroscopy*

AC glow discharges were generated in atmospheric pressure by applying high voltage AC in the range of 3500-15000 V to a pair of stainless steel electrodes separated by an air gap. The discharges were characterized by optical emission spectroscopy (OES) and continuous wave cavity ringdown spectroscopy (cw-CRDS). The electronic (T$_{ex})$, vibrational (T$_{v})$, and rotational (T$_{r})$ temperatures were measured. Spectral stimulations of the emission spectra of several vibronic bands of the 2$^{nd}$ positive system of N$_{2}$, the 1$^{st}$ negative system of N$_{2}^{+}$, the (0,1,2,3-0) bands of NO (A-X), and the (0-0) band of OH (A-X), which were obtained under various plasma operating conditions, show that T$_{r}$, T$_{v}$, and T$_{ex}$ are in the ranges of 2000 - 3800, 3500 - 5000, and 6000 - 10500$^{ }$K, respectively. Emission spectra show that OH concentration increases while NO concentration decreases with an increase of electrode spacing. The absorption spectra of H$_{2}$O and OH overtone in the near infrared (NIR) were measured by the cw-CRDS with a telecommunications diode laser at wavelength near 1515 nm.