Exciton and intracenter radiative recombination in ZnMnTe and CdMnTe quantum wells with optically active manganese ions

The emission spectra of Zn_1?x Mn _x Te/Zn_0.6Mg_0.4Te and Cd_1?x Mn _x Te/Cd_0.5Mg_0.5Te quantum-well structures with different manganese concentrations and quantum-well widths are studied at excitation power densities ranging from 10⁵ to 10⁷ W cm^?2. Under strong optical pumping, intracenter luminescence of Mn²⁺ ions degrades as a result of the interaction of excited managanese ions with high-density excitons. This process is accompanied by a strong broadening of the emission band of quantum-well excitons due to the exciton-exciton interaction and saturation of the exciton ground state. Under pumping at a power density of 10⁵ W cm^?2, stimulated emission of quantum-well excitons arises in CdTe/Cd_0.5Mg_0.5Te. The luminescence kinetics of the quantum-well and barrier excitons is investigated with a high temporal resolution. The effect of the quantum-well width and the managanese concentration on the kinetics and band shape of the Mn²⁺ intracenter luminescence characterized by the contribution of the manganese interface ions is determined.     

Thermochemistry of complex salts of transition metals with tetrazolyl ligands

A combined use of precise combustion calorimetry and reaction calorimetry made it possible to obtain the standard enthalpy of formation of complex salts of transition metals (nickel, zinc, and cadmium) with 2-(1H-1,2,3,4-tetrazol-1-yl)acetohydrazide ligands. The enthalpy of combustion of the ligand was determined using combustion calorimetry, based on which its standard enthalpy of formation was calculated. For measurements by reaction calorimetry, a thermochemical cycle was designed to determine the standard enthalpy of formation of complex salts. The enthalpies of solution in water and in a 0.1 N hydrochloric acid solution of the ligand and complex transition metal salts were measured. Based on these data, the enthalpy of formation of the salts and the enthalpy of formation of three new complex ions were calculated.     

Achromatic reconstruction of the wave front of femtosecond laser pulses

Wave-front reconstruction by geometric-optical reflection of the reconstructing radiation from interference surfaces of a structure recorded in the bulk of a medium by counterpropagating laser pulses is observed. The recording is done with the aid of a sapphire titanate laser. Pulse durations of 30–40 fs are used. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 5, 388–390 (10 March 1997)     

Spatial amplification of a laser wave and the transverse spread of electrons in an undulator with a noncollinear configuration

The spatial amplification of a wave in a magnetostatic undulator with noncollinear electron and laser beams is studied in the framework of the dispersion relation for single-frequency and collective regimes. The dependence of the gain on the electron beam width is estimated with regard to the spatial boundedness of the beams. The laser power threshold at which the selection with respect to the transverse velocity is possible is obtained for a free-electron laser without inversion.     

Optical control of the anisotropy of the orientation of molecules in a liquid

The control of the anisotropy of the orientation of molecules in pure 1,2-dichlorobenzene, C₆H₄Cl₂ at room temperature is demonstrated experimentally. To accomplish the optical control, the medium is exposed to non-resonant excitation with two successive linearly polarized laser pulses with a duration of 60 fs. The state of transient anisotropy is probed with the third pulse by detecting the ultrafast optical Kerr effect via optical heterodyne detection and synchronous demodulation. It is shown that variations in the two parameters, the delay time between two pump pulses, and the angle between the polarization directions of the pump pulses ensure the control of the anisotropy of the orientation of molecules in the subpicosecond region. Original Russian Text ? V.G. Nikiforov, G.M. Safiullin, A.G. Shmelev, A.V. Leont’ev, V.S. Lobkov, 2007, published in Pis’ma v Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2007, Vol. 86, No. 10, pp. 757–761.     

Band structure and broadband compensation of absorption by amplification in layered optical metamaterials

The frequency dependence of the gain required to compensate for absorption is determined for a layered structure consisting of alternating absorbing and amplifying layers. It is shown that the fulfillment of the same conditions is required for the existence of a band structure consisting of alternating bands allowed and forbidden for optical radiation propagation in the frequency-wave vector parametric region. Conditions are found under which the gain required for compensation is smaller than thresholds for absolute (parasitic lasing) and convective (waveguide amplification of radiation) instabilities.     

Physical principles of forecasting the characteristics of the ELF environmental electromagnetic background noise from the meteorological factors

Physical principles of forecasting the environmental electromagnetic background noise (EMBN) characteristics in the extra low frequency (ELF) range are suggested in the work based on an analysis of the meteorological conditions. Dependences of the spectral EMBN characteristics in the ELF range on the meteorological parameters such as the atmospheric pressure, ground wind velocity, temperature, and relative air humidity are obtained. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 89–94, September, 2008.     

Photoluminescence and EPR of porous silicon formed on <Emphasis Type="Italic">n</Emphasis><Superscript>+</Superscript> and <Emphasis Type="Italic">p</Emphasis><Superscript>+</Superscript> single crystals implanted with boron and phosphorus ions

The effect of combined doping by shallow donor and acceptor impurities on boosting the quantum yield of porous-silicon photoluminescence (PL) in the visible and near IR range was studied using phosphorus and boron ion implantation. Nonuniform doping of samples and subsequent oxidizing annealing were performed before and after porous silicon was formed on silicon single crystals strongly doped by arsenic or boron up to ≈10¹⁹ cm^?3. The concentration of known P_b centers of nonradiative recombination was controlled by electron paramagnetic resonance. It is shown that there is an optimal joined content of shallow donors and acceptors that provides a maximum PL intensity in the vicinity of the red part of the visible spectrum. According to estimates, the PL quantum yield in the transitional n ⁺⁺-p ⁺ or p ⁺⁺-n ⁺ layer of porous silicon increases by two orders of magnitude as compared to that in porous silicon formed on silicon not subjected to ion irradiation.     

Absorption and emission of terahertz radiation in doped GaAs/AlGaAs quantum wells

Spontaneous emission of terahertz radiation from structures with GaAs/AlGaAs quantum wells in a longitudinal magnetic field has been studied. It is shown that some bands in the emission spectrum can be related to radiative electron transitions between resonant and localized impurity states, as well as to the transitions with participation of subband states. The temperature dependence of the equilibrium intraband absorption of terahertz radiation and its modulation in a longitudinal electric field in GaAs/AlGaAs quantum wells has been investigated.