The role of spontaneous relaxation in the three-photon ionization of Ba through the two-photon resonant 5d7s ³D₂ state

The influence of spontaneous relaxation on the multiphoton ionization process is considered. Experimental and theoretical investigations have shown that with a comparable weak field there is an interval of low stability of the ionization process, when the probabilities of the competing processes of spontaneous relaxation and ionization are nearly equal. It leads to the unusually rapid growth of the amplitude of the discrete two-photon 5d7s ³D₂ resonance in the yield of Ba⁺, when the field strength was increased very little.