2014, Pavlov, S.G., Deßmann, N., Shastin, V.N., Zhukavin, R.K., Redlich, B., van der Meer, A.F.G., Mittendorff, M., Winnerl, S., Abrosimov, N.V., Riemann, H., Hübers, H.-W.

Stimulated emission in the terahertz frequency range has been realized from boron acceptor centers in silicon. Population inversion is achieved at resonant optical excitation on the 1Λ8+ → 1Λ7- , 1Λ6-, 1Λ8- intracenter transitions with a midinfrared free-electron laser. Lasing occurs on two intracenter transitions around 1.75 THz. The upper laser levels are the 1Λ7- , 1Λ6- , and 1Λ8- states, and the lower laser level for both emission lines is the 2Λ8+ state. In contrast to n-type intracenter silicon lasers, boron-doped silicon lasers do not involve the excited states with the longest lifetimes. Instead, the absorption cross section for the pump radiation is the dominating factor. The four-level lasing scheme implies that the deepest even-parity boron state is the 2Λ8+ state and not the 1Λ7+ split-off ground state, as indicated by other experiments. This is confirmed by infrared absorption spectroscopy of Si:B.

2020, Pavlov, S.G., Deßmann, N., Pohl, A., Zhukavin, R.K., Klaassen, T.O., Abrosimov, N.V., Riemann, H., Redlich, B., Van Der Meer, A.F.G., Ortega, J.-M., Prazeres, R., Orlova, E.E., Muraviev, A.V., Shastin, V.N., Hübers, H.-W.

Transient-type stimulated emission in the terahertz (THz) frequency range has been achieved from phosphorus doped silicon crystals under optical excitation by a few-picosecond-long pulses generated by the infrared free electron lasers FELIX and CLIO. The analysis of the lasing threshold and emission spectra indicates that the stimulated emission occurs due to combined population inversion based lasing and stimulated Raman scattering. Giant gain has been obtained in the optically pumped silicon due to large THz cross sections of intracenter impurity transitions and resonant intracenter electronic scattering. The transient-type emission is formed under conditions when the pump pulse intervals exceed significantly the photon lifetime in the laser resonator. © 2020 Author(s).