  We study theoretically and numerically spasing conditions and optical
dynamics of a composite hyperbolic metamaterial interacting with gain
molecules. By combining Maxwell-Bloch equations with Green's function approach,
we calculate lasing frequency and threshold population inversion for various
gain density in the gain layer. We demonstrate high level of enhancement for
photonic density of states in spacious spectral range provided by hyperbolic
metastructures. We find that direct dipole-dipole interactions between
molecules in the gain layer has a negligible effect on spasing conditions. We
identify a region of parameters in which spasing can occur considering these
effects.
