Microplasmas as vacuum ultraviolet source for Cl-atom density measurements by resonance absorption spectroscopy

A micro-hollow cathode discharge was used to generate radiation on the chlorine atom resonance lines. Such radiation could be used to measure, by resonance absorption spectroscopy, the density of chlorine atoms in either ground state (3p(5) (2)P(3/2)) or in the fine structure metastable state (3p(5) (2)P(1/2)), which is located at 882.35 cm(-1). Among the nine analysed lines in the 132-142 nm spectral region, only those at 137.953 and 139.653 nm, which are strong enough and are not affected by the self-absorption, can be used for the resonance absorption diagnostic of the ground state and the metastable state, respectively. The best operating conditions of the lamp source are 0.5% of Cl(2) in argon at 150 mbar and 4mA discharge current. The measured 800 +/- 30K gas temperature of the microplasma, indicates that under these specific conditions, these two lines are dominantly Doppler broadened. So their profile is Gaussian shaped with full widths at half maximum of (4.7 +/- 0.1) x 10(-4) nm.