  The theory of dynamic conductivity of nanosystem is developed within the
model of rectangular potentials and different effective masses of electron in
open three-barrier resonance-tunnel structure in a constant homogeneous
electric field. The application of this theory for the improvement of operating
characteristics of quantum cascade laser active region (for the experimentally
investigated In$_{0.53}$Ga$_{0.47}$As/In$_{0.52}$Al$_{0.48}$As heterosystem)
proves that for a certain geometric design of nanosystem there exists such
minimal magnitude of constant electric field intensity, at which the
electromagnetic field radiation power together with the density of current
flowing through the separate cascade of quantum laser becomes maximal.
