Generation of continuous-wave terahertz radiation by use of quantum interference

We propose a scheme for the generation of continuous-wave terahertz (THz) radiation. The scheme requires a medium in which three discrete states in a Lambda configuration can be selected, with the THz frequency transition being between the two lower metastable states. The propagation of three-frequency continuous-wave electromagnetic (EM) radiation through a Lambda medium is considered. Under resonant excitation, the medium absorption can be strongly reduced owing to quantum interference of transitions, whereas the nonlinear susceptibility is enhanced. This leads to efficient energy transfer among the EM waves, providing the possibility of THz generation. We demonstrate that the photon conversion efficiency is approaching unity in this technique. (C) 2000 Optical Society of America [S0740-3224(00)00208-3] OCIS codes: 190.2620, 190.4410, 270.1670, 020.1670.