Terahertz optically pumped silicon lasers

Stimulated terahertz (THz) emission from silicon single crystals doped by group-V donors has been obtained by optical excitation with pulsed infrared lasers. Pumping by a conventional TEA CO2 laser results in lasing on discrete lines between 1.3 and 7 THz (see figure). Laser thresholds can be as low as 10 kW/cm2. They depend on the donors species and the laser mechanism. Intracentre population inversion is realized between particular excited states which are large-spaced due to the chemical shift of the donor binding energy. The lifetime of an electron in an excited state (up to ~70 ps) is determined by the efficiency of phonon-assisted nonradiative relaxation. Optical excitation by the emission of a frequency-tunable free electron laser results in two different types of lasing. At relatively low pump intensities (~1 kW/cm2) the intracentre mechanism of lasing is dominating. At pump intensities above ~100 kW/cm2 stimulated scattering of pump photons on transverse acoustic intervalley phonons can occur in the vicinity of an impurity atom. This results in laser emission in the frequency range from 4.6 to 5.8 THz. In this case the laser frequency can be tuned proportionally to the pump frequency

THz lasing from donor centers in uniaxially stressed silicon

Recent results of experimental and theoretical studies of THz stimulated emission from optically excited group-V shallow donor centers (P, Sb, As, Bi) in uniaxially stressed silicon are reviewed and discussed. Low-temperature intracenter phonon-assisted relaxation responsible for the population inversion of bound excited states, the lifetime of principle states and small signal gain available on donor intracenter transitions are considered. The summary of the laser performance differed for differing donor centers is analyzed. Special attention is paid to the effects of essential enhancement of small signal gain, laser threshold diminution and switching of the laser transition in As donor under the strain

Terahertz Raman laser based on silicon doped by phosphorus

Raman-type simulated emission at frequencies between 5.0 and 5.2 THz as well as between 6.1 and 6.4 THz has been realized in silicon crystals doped by phosphorus donors. The Stokes shift of 3.16 THz is equal to the difference between the energies of the phosphorus ground state, 1 s(A1), and the 1 s(E) excited state

Stimulated Terahertz Stokes Emission of Silicon Crystals Doped with Antimony Donors

Stimulated Stokes emission has been observed from silicon crystals doped by antimony donors when optically excited by radiation from a tunable infrared free electron laser. The photon energy of the emission is equal to the pump photon energy reduced by the energy of the intervalley transverse acoustic (TA) g-phonon in silicon (2.92 THz). The emission frequency covers the range of 4.6–5.8 THz. The laser process occurs due to a resonant coupling of the 1s(E) and 1s(A1) donor states (separation 2.97 THz) via the g-TA phonon, which conserves momentum and energy within a single impurity center

First terahertz-range experiments on pump – probe setup at Novosibirsk free electron laser

A single-color pump-probe system has been commissioned at the Novosibirsk free electron laser. The laser emits a tunable monochromatic terahertz radiation. To prove the proper system operation, we investigated the time-resolved absorption of a sample of n-type germanium doped with antimony, which was previously investigated at the FELBE facility, in the temperature range from 5 to 40 K. The measured relaxation time amounted to about 1.7 ns, which agreed with the results obtained at the FELBE. The results of pump-probe measurements of non-equilibrium dynamics of hot electrons in the germanium crystal at cryogenic temperatures are presented for wavelengths of 105, 141 and 150 μm