Stimulated terahertz emission due to nonlinear frequency conversion in silicon

New principals to generate stimulated emission in terahertz frequency range from silicon doped by shallow donor centers have been demonstrated. Lasing in the frequency bands of 1.2-1.8 THz; 2.5-3.4 THz, 5.0-5.2 THz and 6.1-6.4 THz, has been achieved from silicon crystals doped by phosphorus to ~10¹⁵ cm^-3, 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 Stokes-shifted Raman-type lasing, the shift is determined by the 1s(E)-1s(A₁) donor electronic resonance. The low-frequency bands indicate on high-order nonlinear frequency conversion processes accompanied by high-energy intervalley phonons of host lattice.