Selective Excitation Spectroscopy and Some Possible Applications

Abstract

If an atomic transition is optically pumped by a beam of laser radiation, having the appropriate frequency, the population in the upper state of the transition can be considerably enhanced along the path of the beam. This will give rise to an intensification of the spontaneous emission originating from this upper state in the region localized by the beam. Such intensified emission contains information about the conditions within the pumped region and can, under certain conditions, be identified from the background radiation. It is shown that this process called ``selective excitation spectroscopy'' can be used in a variety of ways, one of the most important being the determination of the local values of electron temperature and density in low-temperature plasmas. This technique is illustrated for both potassium- and barium-seeded plasmas. Furthermore, because this technique involves a pulsed laser, temporal as well as spatial resolution is possible.