Si. Derzhavin et al., 3-LEVEL SYSTEM WITH COHERENCE FORMED VIA CONTINUUM STATES FOR INVERSIONLESS AMPLIFICATIONS OF RADIATION, Laser physics, 5(1), 1995, pp. 118-125
A three-level system with coherence formed by transitions via continuu
m states in an additional (driving) electromagnetic field was consider
ed 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 p
ossible only in the case of rather small intensity of the amplified fi
eld when the Rabi frequency is less than the separation between two up
per levels. Otherwise, in the case of higher intensities, absorption o
f 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 onl
y in the weakly inversionless situation, when the populations of upper
and lower levels are almost equal to each other. The strong inversion
less situation corresponds to the nonlinear regime of amplification.