Abstract The paper states a simple and analytically solvable model for the terahertz generation via a localized excited ensemble of identical three-level quantum particles within the resonator.
Abstract 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.
In this work, difference-frequency generation is theoretically analysed for the three-level quantum system, having forbidden in dipole approximation electronic and optically active vibration transitions from the ground state. Excitation of coherent phonon polaritons wave in the terahertz frequency range by an ultrashort optical pulse, being in the visible or near-infrared spectral regions, and injected pulse with frequency almost twice that of the pump is considered. Dynamics of terahertz radiation arising during excitation of both electronic and vibrational coherences at the two-photon and combined resonances in the ensemble of three-level quantum systems was evaluated.