Ultrafast Population Inversion without the Strong Field Catch: The Parallel Transfer

Quantum systems with sublevel structures, like molecules, prevent full population inversion from one manifold of sublevels to the other using ultrafast resonant pulses. We explain the mechanism by which this population transfer is blocked. We then develop a novel concept of geometric control, assuming full or partial coherent manipulation within the manifolds, and show that by preparing specific coherent superpositions in the initial manifold, full population inversion or full population blockade, that is, laser transparency, can be achieved. By properly choosing the relative phases of the initial state, one can interfere in the stimulated emission process, changing the pattern of Rabi oscillations so that full population inversion to the excited electronic state can be achieved almost regardless of the pulse intensity after a minimal threshold value. This is the basis of a novel control mechanism, termed parallel transfer.