Abstract
The recently observed efficient ionization of sodium vapor by a laser tuned to the sodium resonance line can be explained in terms of the large population of resonance‐state atoms created by laser‐induced radiative equilibrium. This large population of excited atoms represents (a) a reservoir of energy that can rapidly be transferred to the free electrons via superelastic collisions and (b) a source of pseudo‐ground‐ state atoms possessing a much reduced ionization energy. Three‐photon ionization is proposed as the mechanism for creation of the primary pool of free electrons.