Superfluorescence without inversion in coherently driven three-level systems

A superfluorescence effect in a V-type medium with initial Raman inversion, driven by a strong coherent held on one of the transitions, is studied ana lytically and numerically. It is shown that the collective spontaneous emis sion evolves in the presence of a minor population of an upper state of a s uperfluorescent transition. In the limit of the Rabi frequency of a driving field large compared to that of a superfluorescent pulse, the system of tw o equations for the fields and density-matrix equations for three states of the medium is reduced to Maxwell-Bloch equations for an effective two-leve l system. The shape of a superfluorescent pulse is perfectly described in t erms of a slowly varying envelope function (which is a solution of the Maxw ell-Bloch equations), filled with fast oscillations associated with Rabi fl oppings on the driving transition. In the average, i.e., after integrating over a period of Rabi oscillations, the upper superfluorescent state is pop ulated less than other states, such that the phenomenon may be called "supe rfluorescence without inversion" by analogy with lasing without inversion. [S1050-2947(99)04408-X].