Exceeding the Manley-Rowe quantum efficiency limit in an optically pumped THz amplifier

Using a microscopic theory based on the Maxwell-semiconductor Bloch equations, we investigate the possibility of an optically-assisted electrically-driven THz quantum cascade laser. Whereas in optical conversion schemes the power conversion efficiency is limited by the Manley-Rowe relation, the proposed optically-assisted scheme can achieve higher efficiency by coherently recovering the optical pump energy. Furthermore, due to quantum coherence effects the detrimental effects of scattering are mitigated.