Modeling of high pressure rare gas plasmas excited by an energetic flash x-ray source

The need for new tunable sources in the UV-VUV region, driven by the many diverse applications in material processing, microtechnics, microelectronics hor-ellipsis, have reawakened interest in studies of high pressure rare gas (Rg) and mixtures of rare gas plasmas. Recently, special attention has been given to the study of the broad fluorescences (often called open-quotes third continuumclose quotes) of rare gas ionic excimers radiating in the UV-VUV range. They have been produced efficiently in a variety of experiments in which high pressure samples have been excited by protons, α particles, heavy ion beams, electron beams, silent discharges and flash X-ray sources. Rare gas ionic excimers can be considered as candidates for a new class of tunable laser in the UV-VUV and, indeed, very recently Qi et al reported the first observation of laser oscillation attributed to Ar22+* around 213 nm. In a recent work, our experimental results obtained over a very extended pressure range (0.1-30 bar) have clearly shown that the so-called third continuum was in fact composed of many different spectral components which relative intensity depend on pressure and, in pulsed operation as it was, time in the afterglow. For example, in argon, we put in evidence five different continua between 150 and 300 nm located around 160, 185, 200, 220 and 245 nm. If undoubtedly attributed to ionic molecular species, the exact origins of these different spectral components remain unknown and are still under discussion. At this time, it appears that both Rg2+* and Rg2++* can be involved, probably together with heavier ionic clusters