Terahertz-range stimulated emission due to electronic nonlinear frequency conversion in silicon

Silicon-based semiconductors offer optically low-loss and high-thermal-conducting lattice for the broad-band terahertz active media that can be used in the range of 5-7 THz. We report on realization of the terahertz-range stimulated emission from monocrystalline natural and isotopically enriched silicon crystals doped by group-V donor centers due to nonlinear frequency conversion. Lasing in the frequency bands of 1.2 - 1.8 THz; 2.5 - 3.4 THz has been achieved from silicon crystals doped by phosphorus and in the frequency band of 4.6 - 6.4 THz from different donors under optical pumping by radiation of mid-infrared free electron laser at cryogenic temperatures. Analysis of the data shows that the emission in high-frequency band corresponds to electronic Stokes-shifted Raman-type lasing. The low-frequency bands indicate on high-order nonlinear frequency conversion processes similar to four-wave mixing accompanied by highenergy intervalley g-phonons and f-phonons of host lattice. These lasers supplement terahertz silicon lasers operating on transitions between donor states.