Self-induced transparency of few-cycle terahertz pulses

A new integrable system of equations that describes the effect of self-induced transparency for few-cycle terahertz pulses propagating in a system of resonant tunnel transitions is obtained. This system is derived within an approach based on the concept of envelopes for the electric field of a pulse and dipole moments of resonant and nonresonant transitions involved in the interaction with it. This approach makes it possible to describe solitons, whose velocity can be much less than the linear group velocity of light in the medium. This distinguishes it favorably from the method in which the concept of envelopes is not used but the density of the medium is assumed to be low.