ABSTRACT
INTRODUCTION Environmental awareness has attracted the research efforts into searching for an alternative chemical element to directly replace the toxic mercury used in fluorescent lamps [1-2]. Xenon emits strong radiation in the ultra-violet (UV) region and hence is one of the most promising candidates as an alternative to mercury. Nevertheless, the UV radiation efficiency from a xenon discharge is in general lower than that from mercury discharge. Besides, the positive column of a xenon discharge tends to contract at high current density and the intensity of the phosphor-converted emissions from a contracted discharge is very low. One of the ways to suppress the contraction and to enhance the efficiency is to make the "off' period in the voltage waveform, i.e. pulsed discharge. In a pulsed discharge, processes in a xenon plasma such as ionization, excitation, emission and so on are greatly different from that in steady state discharges such as DC, AC and RF. Thus, efficiency and characteristics of the contraction in the pulsed discharge are different but its mechanisms are not well known. In the pulsed mode, behavior of the metastable atoms is one of the most important parameters to understand the processes in the plasma because its lifetime is long and they stay in the "off' period. In this study, we measured temporal behavior of the spatial distribution of xenon metastable atoms by IR laser absorption spectroscopy.
