Population densities of Fe I and Fe II levels in an atomic beam from partially saturated LIF signals

Laser-induced fluorescence has been used to measure number densities of the ground states and of various metastable states of Fe I and Fe II in an atomic beam. The iron atoms and ions have been generated in a hollow cathode discharge from where they were extracted as an effusive beam. The densities were calibrated via Rayleigh scattering in nitrogen. Number densities of - were obtained from measurements on a volume. Saturation in the LIF signals has been studied both experimentally and theoretically. The spatial dependence of the saturation due to the spatial distribution of the laser pulse energy proved to be essential. Thus, the LIF signals are partially saturated. A theoretical model is presented enabling an adequate description of the partially saturated LIF signals, and an extrapolation of these signals into the unsaturated regime yields absolute number densities. The various systematic error sources including the influence of linearly polarized laser radiation are discussed.