Investigation of optical amplification of Cu II 224.7 nm spectral line in multiple segmented Grimm discharge

Abstract

In this study the resonance energy transfer from metastable argon ion to copper atom in an argon glow discharge is used to investigate posibility of inverse population of the upper energy level of the line Cu II 224.7 nm. This resonance energy transfer is very efficient due to small difference between the energy levels of Ar II (3p5,2P1/2) and Cu II (4p,3P2). In order to examine the possibility of obtaining the inverse population of this copper ion level, arrangement of eight aligned catodes of Grimm-type abnormal glow discharges has been assembled. The length of the active medium is changed, by varying the number of the active discharges while the intensity of the Cu II line is monitored. It has been found that the increase of the line intensity is not a linear function of the active medium length. This can be considered as the first indication of an optical amplification of mentioned Cu II line and a possibility to achieve an inverse population on Cu II (4p,3P2) level. Since the intensity of this copper ion line depends on the discharge current, dependence of the Cu II line intensity on the plasma length for different currents is recorded. In order to achieve higher line intensity of Cu II 224.7 nm line, instead of DC power supply, a laboratory made pulse generator has been used. The device enables high intensity current pulses through the discharge and consequently increased the population of the excited level of copper ion. To determine parameters of the most efficient pulse regime, dependence of the Cu II line intensity on pulse duration has been studied.