Generation of Extremely Short Pulses of Terahertz Radiation Based on Superradiation of a Three-Level Resonant Medium

The possibility of generating extremely short pulses of terahertz (THz) radiation due to superradiance-collective spontaneous emission 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 arises in the interval between its excitation and deexcitation. 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 a terahertz superradiance pulse is discussed.