  Laser-induced fluorescence (LIF) is a powerful tool in studying wave-particle
interactions, velocity-space diffusion and other phenomena in plasmas under the
proper conditions. Ignoring the possible instrumental errors in LIF, such as
metastable lifetime effects, may result in unreliable measurements. LIF is
frequently performed on metastable states that are produced from direct
ionization of neutral gas particles and ions in other electronic states.
However, the metastable population born from neutrals cannot faithfully
represent processes which act on the ion dynamics in a time shorter than the
metastable lifetime. A numerical simulation is performed to study the
metastable lifetime effects using a Lagrangian approach for LIF. A theoretical
model in determining the fraction of metastable ions produced from direct
ionization is reported to provide corrections to the LIF measurements.
