Creation of efficient sources of terahertz (THz) radiation is of high importance for various fields of modern technology, including information transfer, biosensing, security and others. These applications are currently limited due to the lack of compact and reliable solid state sources of THz radiation. Recently we have proposed that the emission rate of THz photons may be increased by bosonic stimulation if the THz transition feeds a condensate of exciton-polaritons . We have developed a quantum theory of vertical cavity surface emitting terahertz lasers. The vertical terahertz lasing coexists with polariton lasing and, consequently, is characterised by a low pumping threshold. The resonant two photon pumping of 2p exciton states in such a cavity may be assured by a conventional vertical cavity light emitting diode (VCLED) emitting in red. The terahertz radiation will be emitted due to the transition from 2p-exciton state to 1s exciton-polariton state, which is expected to be stimulated by the occupation number of the 1s state which may achieve 10000 in the polariton lasing regime. Further improvement of quantum efficiency of bosonic terahertz lasers may be achieved taking advantage of a cascade effect in a parabolic trap where the THz transition between equidistant exciton energy levels is optically allowed . Bosonic cascade lasers are predicted to achieve quantum efficiencies of 500-700% in realistic structures.
 A.V. Kavokin, I.A. Shelykh, T. Taylor and M.M. Glazov, Vertical Cavity Surface Emitting Terahertz Lasers, Phys. Rev. Letters, 108, 197401 (2012).
 T.C.H. Liew, M.M. Glazov, K.V. Kavokin, I.A. Shelykh, M.A. Kaliteevski, and A.V. Kavokin, Proposal for a Bosonic Cascade Laser, Phys. Rev. Letters, 110, 047402 (2013).