Terahertz emission from lithium doped silicon under continuous wave interband optical excitation

We report on experimental observation and study of terahertz emission from lithium doped silicon crystals under continuous wave band-to-band optical excitation. It is shown that radiative transitions of electrons from 2P excited states of lithium donor to the 1S(A1) donor ground state prevail in the emission spectrum. The terahertz emission occurs due to capture of nonequilibrium electrons to charged donors, which in turn are generated in the crystal as a result of impurity assisted electron-hole recombination. Besides the intracentre radiative transitions the terahertz emission spectrum exhibits also features at about 12.7 and 15.27 meV, which could be related to intraexciton transitions and transitions from the continuum to the free exciton ground state

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

Prospects of the application of curable decontamination solutions in problems of impact improving of nuclear power plants

The technology of power generation from nuclear power is accompanied by the formation of radioactive waste, which has significant potential environmental hazards. This paper proposes new methods of decontamination of NPP equipment with fluids that immediately after use can be converted into an environmentally safe condition - curing methods of decontamination solutions. A characteristic feature of curable solutions decontamination methods is that the composition of the decontamination solution, and also processes in the solution during deactivation, affect the subsequent transfer of this solution to a solid state, as well as on the properties of the matrix, which will be "sealed" removed radionuclides. The main factor determining the course of the process of decontamination methods can be divided into contact, acid-abrasive, ultrasound and combined. Concerning the main component of the decontamination solution (slurry) methods can be subdivided into solutions with hydraulic binders, clay slurry (with conventional clay and a clay with a high alumina content) suspension of diatomite and combined. The means of transfer of the solutions used in the solid state methods are divided into "self-curing" heat treatable and cemented. Application of methods of the curing solution allows us to reduce the number of operations to deactivate air conditioning that provides economic benefits and allows us to create a whole class of portable equipment and to reduce the amount ongoing to dump 4-6 times in comparison with cemented. © 2014 WIT Press.International Journal of Safety and Security Engineering;International Journal of Sustainable Development and Planning;WIT Transactions on Ecology and the Environmen

Terahertz lasers based on intracentre transitions of group V donors in uniaxially deformed silicon

This paper presents a brief overview of available experimental data on the characteristics of stimulated terahertz emission (4.9 – 6.4 THz) from optically excited neutral group V donors (phosphorus, antimony, arsenic and bismuth) in crystalline silicon subjected to uniaxial compressive strain along the [100] axis. Strain is shown to have a significant effect on the characteristics in question. Optimal strain depends on the dopant and may reduce the threshold pump intensity and improve lasing efficiency. We discuss possible mechanisms behind this effect and estimate the limiting output emission parameters

Injection-seeded internal-reflection-mode p-Ge laser exceeds 10 W peak terahertz power

Injection seeding of a large active p-Ge laser crystal operating on total internal reflection modes is demonstrated with peak output power at the level of 40 W in the 1.5-4.2 THz spectral range. The improvement over traditional 1 W axial mode p-Ge lasers is due both to spatially and temporally more efficient use of the available population inversion

Pulse separation control for mode-locked far-infrared p-Ge lasers

Active mode locking of the far-infrared p-Ge laser giving a train of 200 ps pulses is achieved via gain modulation by applying an rf electric field together with an additional bias at one end of the crystal parallel to the Voigt-configured magnetic field. Harmonic mode locking yields a train of pulse pairs with variable time separation from zero to half the roundtrip period, where pulse separation is electrically controlled by the external bias to the rf field

Relaxation of Coulomb States in semiconductors probed by FEL radiation

This article has no abstract