Isotopically selective two-photon excitation of a three-level atom

A theoretical analysis is made of the process of isotopically selective excitation of atoms in the field of opposite waves when the compensation of the Doppler broadening is incomplete. The density matrix formalism for a homogeneous steady-state case is used to obtain expressions for the total probability of the excitation of resonating and nonresonating isotopes and for the selectivity of the process defined as the ratio of these probabilities. In some cases analytic expressions are obtained and these make it possible to determine the nature of the dependence of the total probability of the excitation and selectivity on the temperature of a vapor, buffer gas concentration, ratio of the Rabi transition frequencies, detuning from a resonance, and isotopic shifts. Numerical estimates are obtained of the atomic parameters for transitions in potassium and rubidium atoms. It is shown that the adopted method is more promising for the separation of the isotopes of alkali metals than is one-photon excitation.