The observation of far-infrared stimulated emission from shallow donor transitions in silicon is reported. Lasing with a wavelength of 59 &mgr;m due to the neutral donor intracenter 2p(0)-->1s(E) transition in Si:P pumped by CO2 laser radiation is obtained. Populations of D0 and D- center states and the balance of the radiation absorption and amplification are theoretically analyzed.

The frequency of a terahertz quantum-cascade laser is stabilized to the absorption line of methanol gas at a frequency of 2.55 THz. The method is based on frequency modulation of the laser emission across the absorption line. The resulting derivativelike signal is used as an error signal for a control loop that keeps the laser frequency at maximum absorption. The unstabilized laser that is operated in a pulse tube cooler has frequency fluctuations of 15 MHz, which are reduced to 300 kHz with the control loop in action. The line shape of the locked signal is Gaussian

Far-infrared stimulated emission from optically pumped neutral Bi donors in silicon has been obtained. Lasing with wavelengths of 52.2 and 48.6 μm from the intra-center 2p±→1s(E:Γ8),1s(T2:Γ8) transitions has been realized under CO2 laser pumping. The population inversion mechanism is based on fast optical-phonon-assisted relaxation from the 2p0 and 2s excited states directly to the ground 1s(A) state leading to relatively small population in the intermediate 1s(E), 1s(T2) excited states.

A liquid cryogen-free terahertz heterodyne receiver in a pulse tube cooler has been realized. The receiver operates at 2.5 THz. It is based on a quantum cascade laser (QCL) as local oscillator and a hot electron bolometric mixer. A detailed study of the QCL beam quality yielded a beam propagation factor of 1.1-1.2. The double sideband noise temperature of the system is 2000 K and when corrected for optical losses in the signal path it is similar to 800 K. (C) 2008 American Institute of Physics

Two mechanisms of the inverse population of shallow impurity states in silicon under optical pumping have been proposed and analyzed, using a procedure allowing to reduce the number of required matrix elements of transitions. The first mechanism is based on the resonance interaction of the 2p 0 state in Si : Bi with optical phonons. The other one is based on the suppression of acoustic-phonon-assisted relaxation from the 2p 0 state in Si : P due to the momentum conservation law. Spontaneous emission was registered from shallow donors in Si : P under photoionization by a CO 2 laser. The dependence of the spontaneous emission intensity on the intensity of pumping radiation confirms the possibility of amplification on impurity transitions.

No abstract

Single axial-mode operation of the pulsed far-infrared p-Ge laser with an intracavity Fabry–Perot type frequency selector has been observed by means of Fourier-transform spectroscopy. A spectral resolution better than 1 GHz has been achieved on an ordinary continuous-scan spectrometer using the event-locked technique for pulsed emission sources. A laser active-cavity finesse of at least unity has been directly confirmed from the measured emission spectral width. Analysis of the envelope of the corresponding interferogram suggests that the finesse exceeds 10.

Investigations of the dynamics of the far-infrared p-Ge laser emission reveal strong periodic soliton-like intensity spikes with less than 100 ps duration. We interpret these spikes as self-mode-locking of p-Ge laser modes. The effect becomes more pronounced when a GaAs/ AlGaAs/InGaAs quantum well structure on a semi-insulating GaAs substrate is inserted into the laser cavity.