3-LEVEL SYSTEM WITH COHERENCE FORMED VIA CONTINUUM STATES FOR INVERSIONLESS AMPLIFICATIONS OF RADIATION

A three-level system with coherence formed by transitions via continuum states in an additional (driving) electromagnetic field was considered theoretically. It was shown that, in the steady-state regime, both amplification of radiation due to transitions between discrete levels and the inversionless situation are realized simultaneously. This is possible only in the case of rather small intensity of the amplified field when the Rabi frequency is less than the separation between two upper levels. Otherwise, in the case of higher intensities, absorption of radiation and inversion of population occur simultaneously. Effects of the saturation of the amplified field and of population trapping in discrete levels (stabilization) are shown to exist in this system. It was shown that the linear regime of amplification can be realized only in the weakly inversionless situation, when the populations of upper and lower levels are almost equal to each other. The strong inversionless situation corresponds to the nonlinear regime of amplification.