Atomic potassium is ionized by three channels when it is excited by a pulse dye laser. They are energy pooling induced ionization, 4S→6S and 4S→4D two photon resonant three photon ionization. The ionization current intensity at various vapor temperature and laser intensity were investigated for the former two ionization channels. The atomic radiation trapping and nonlinear ionization were found in ionization current spectra. The qualitative explanations for above phenomena are given.
A realistic model for resonant two-photon ionization of an atom is developed which can be solved exactly to give the ionization probability as a function of time, photon intensity, and a few atomic parameters. The exact solutions are compared to various commonly used perturbation results in order to ascertain the regions of validity of the perturbation calculations. It is shown that there are combinations of the parameters for which ionization rates cannot accurately describe the correct results, and that one commonly used perturbation development is not generally applicable to resonant two-photon ionization. Extension of the model to
(n+m)-photon ionization having an
m-photon resonance is discussed. The model is applied to two- and three-photon ionization in Cs.