Double-lambda four-level configuration, coupled to two driving and two probe fields is considered. Explicit formulae, based on density-matrix approach, for the analysis of the conditions of amplification without population inversion both in V and $Lambda configurations are given. Effects of inhomogeneous broadening of the transitions on coherent coupling are discussed. Crucial importance of these effects for the choice of the proper transition schematics is shown. Numerical analysis of the conditions for amplification without inversion and four-wave mixing in the Ne energy-level configuration, relevant to the experiments, which are under way, is given.
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