  A low-pressure double-inductively coupled plasma device is used to study the
fundamental plasma parameters, plasma chemistry, and UV photon emission from
the first excited state of nitric oxide, NO(A), in gas mixtures of nitrogen and
oxygen. In addition to the gas mixture, rf power and gas pressure are varied,
and the E-H mode transition of the inductively coupled plasma is studied
specifically. The gas temperature and UV photon emission are measured by
optical emission spectroscopy (OES), the absolute density of the nitric oxide
electronic ground state by laser-induced fluorescence (LIF), as well as
electron density and electron temperature by a multipole resonance probe (MRP).
A simple collisional-radiative model for UV emission from NO(A) is developed,
which takes the measured densities of ground state nitric oxide and electrons,
as well as the electron temperature and neutral gas temperature, as input
parameters. The results reveal the links between the absolute densities of
ground state nitric oxide, the excitation of this species driven by electron
impact and collisions with nitrogen metastables, quenching of the nitrogen
metastables, and the resulting UV photon emission rate. The density of ground
state nitric oxide is shown to increase with power, while the discharge remains
in E-mode, and to decrease significantly with the transition into H-mode, when
sufficient rf power is deposited in the discharge. Despite the lower densities
of ground state nitric oxide in H-mode, the UV photon emission intensity
increases continuously with higher rf powers and over the E-H transition. This
effect is shown to be caused by increased excitation of NO(A) by nitrogen
metastables in H-mode, which is sufficient to overcompensate the decrease in
ground state nitric oxide density.
