On the signal collection in laser enhanced ionization spectrometry

A theoretical model is developed which relates the experimentally observed signal to the charged species produced in laser enhanced ionization. The model is based on a general equation, which describes the electric field in a flame confined between electrodes at fixed potentials, and a relation for the charge induced on these electrodes. A complete analytical solution is found in a one-dimensional geometry. The signal corresponding to the laser induced electrons is described accurately by the model. The ionic part of the signal, although in most cases negligible, is influenced significantly by dynamic screening in the flame, and requires a more complete model. The theory is applied to an experimental situation, and relations for optimal signal collection are derived. Then the predictions from the theory in a cylindrical geometry are compared to results from a graphite furnace experiment. The temporal behaviour of the signal is further used for a determination of the electron mobility in a flame.