A systematic investigation of N-level inversion schemes, with use of ‘‘chirped frequency lasers,’’ in and beyond the adiabatic limit is presented. (1) It is shown that, contrary to intuition, the favorable scheme for adiabatic inversion requires that, during the process, resonances occur in reversed order, i.e., first the (N-1)-N transition and then backward along the atomic-level ladder down to the transition 1-2. (2) A new multilevel inversion process at fast rates (far beyond the adiabatic limit) is found. Surprisingly, the process occurs for pulse area equal to π in spite of large (time-dependent) detunings. Full analytic explanation of this generalized π pulse inversion is presented. General new properties of the multilevel adiabatic approximation are also derived and discussed.

• Received 4 April 1985

DOI:https://doi.org/10.1103/PhysRevA.32.2776