Generation of extremely short pulses of terahertz radiation based on superradiance of a three-level resonant medium

The possibility of generating extremely short pulses of terahertz (THz) radiation due to superradiance - collective spontaneous emission of stopped polarization of a thin layer of a three-level resonant medium excited by a pair of attosecond (or femtosecond) pulses is studied theoretically. The source of a terahertz pulse is a pulse of stopped nonlinear polarization of the medium, which occurs in the interval between its excitation and de-excitation. The case of a three-level medium with equidistant energy levels (as in a quantum harmonic oscillator), the transition frequency of which lies in the THz range, is considered. The influence of the populations of the excited levels of the medium on the shape of the terahertz superradiance pulse is discussed.