Characterization of a high-pressure microdischarge using diode laser atomic absorption spectroscopy

Abstract

A high-pressure dc glow discharge based on micro-structured-electrode (MSE) arrays was investigated by diode laser atomic absorption spectroscopy. The microdischarge was studied at constant current in pure Ar for pressures ranging from 50 to 400 mbar. The measurements of the absolute population density of the excited 1s5, 1s4, 1s3, and 1s2 levels of Ar in the discharge revealed a population density of excited atoms in metastable and resonance states in the range 1012–1015 cm−3. The gas temperature and the electron number density were evaluated from the analysis of the absorption line profiles, taking into account significant broadening mechanisms. The gas temperature, derived from the Doppler broadening, was found to increase with pressure from 380 K at 50 mbar to 1100 K at 400 mbar. The electron number density was calculated from the Stark broadening and shift, and it ranges from 9×1014 to 5×1015 cm−3. The MSE-sustained discharges are combining the non-equilibrium character with the advantage of high-pressure, which recommends them for non-thermal plasma processing e.g. surface treatment, plasma chemistry and generation of UV and VUV radiation.