A new approach to the development of sources of coherent radiation is studied both theoretically and experimentally. The approach is based on parametric excitation of collective modes of the "field + atoms" system in two-level resonance media without population inversion, with the super-critical coupling between the field and matter subjected to stimulated modulation. The theoretical results include a description of computer simulation of the gain and stimulated emission based on quantitative formalism of the semiclassical theory of laser physics (Maxwell-Bloch equations). Experimental study of coherent light amplification in optically dense media without population inversion was carried out using a multimode pulsed dye laser in the two-wave pump-probe configuration. As the absorbing medium, we used the positive column of a glow discharge with metastable Ne atoms. A qualitative agreement is demonstrated between the data of numerical simulation and experimental spectral characteristics and dynamics of coherent amplification and lasing.