Bosonic cascade terahertz lasers

Emission of terahertz radiation may be stimulated in a bosonic system, where the final state occupation is significant. Polariton lasers represent such a system, which occupation numbers of 10000 or more for a polariton condensate are achievable at room temperature. A set of equally spaced in energy polariton condensates can be created in a parabolic lateral trap in a planar semiconductor microcavity. Pumping one of the highest polariton states in the trap one can induce a cascade of terahertz tranisitons, which would result in terahertz lasing even without the external terahertz cavity. The quantum efficiency of terahertz lasers may achieve 700% according to our extimations.