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

We propose a scheme for the generation of continuous-wave terahertz (THz) r adiation. The scheme requires a medium in which three discrete states in a Lambda configuration can be selected, with the THz frequency transition bei ng between the two lower metastable states. The propagation of three-freque ncy continuous-wave electromagnetic (EM) radiation through a Lambda medium is considered. Under resonant excitation, the medium absorption can be stro ngly reduced owing to quantum interference of transitions, whereas the nonl inear susceptibility is enhanced. This leads to efficient energy transfer a mong the EM waves, providing the possibility of THz generation. We demonstr ate that the photon conversion efficiency is approaching unity in this tech nique. (C) 2000 Optical Society of America [S0740-3224(00)00208-3] OCIS cod es: 190.2620, 190.4410, 270.1670, 020.1670.