Lasing at 1.5 µm in quantum dot structures on GaAs substrates

Lasing at 1488–1515 nm in the temperature range 20–83°C was obtained in structures with an active region based on multiply stacked arrays of self-organized quantum dots grown on GaAs substrates. The threshold current density of a laser with four cleaved facets was 800 A/cm2 at room temperature. The method of wavelength extension is based on the use of a metamorphic buffer layer with an In content of about 20% intended for relieving the lattice mismatch stress.     

High efficiency (ηD>80%) long wavelength (λ>1.25 μm) quantum dot diode lasers on GaAs substrates

Diode lasers based on several layers of self-organized quantum dots (QD) on GaAs substrates were studied. The lasing wavelength lies in the range λ=1.25–1.29 μm, depending on the number of QD layers and optical losses. A record external differential efficiency of 88% and the characteristic temperature of threshold current, 145 K, were obtained. The internal losses, and also threshold and spectral characteristics, are correlated with the optical gain and radiative recombination efficiency, which are strongly dependent on the design of the active region and growth modes.     

Effect of physically active media on yarn orientation strengthening

Conclusions The effect of deforming Oksalon yarn in Various physically active liquid media on its physicomechanical properties has been studied.The action of water or carbon tetrachloride, with simultaneous deformation of the complex yarn, aids in reducing the cementation of elementary filaments, and assists polymer orientation molecular order, and raises the physicomechanical properties of the yarn.In the stage of high-temperature stretching, an increase in the efficiency of orientation strengthening is observed as a result of preliminary deformation of the yarn in physically active media.Translated from Khimicheskie Volokna, No. 3, pp. 27–29, May–June, 1985.     

Test facility for investigation of heat transfer of promising coolants for the nuclear power industry

The results are presented of experimental investigations into liquid metal heat transfer performed by the joint research group consisting of specialist in heat transfer and hydrodynamics from NIU MPEI and JIHT RAS. The program of experiments has been prepared considering the concept of development of the nuclear power industry in Russia. This concept calls for, in addition to extensive application of water-cooled, water-moderated (VVER-type) power reactors and BN-type sodium cooled fast reactors, development of the new generation of BREST-type reactors, fusion power reactors, and thermonuclear neutron sources. The basic coolants for these nuclear power installations will be heavy liquid metals, such as lead and lithium-lead alloy. The team of specialists from NRU MPEI and JIHT RAS commissioned a new RK-3 mercury MHD-test facility. The major components of this test facility are a unique electrical magnet constructed at Budker Nuclear Physics Institute and a pressurized liquid metal circuit. The test facility is designed for investigating upward and downward liquid metal flows in channels of various cross-sections in a transverse magnetic field. A probe procedure will be used for experimental investigation into heat transfer and hydrodynamics as well as for measuring temperature, velocity, and flow parameter fluctuations. It is generally adopted that liquid metals are the best coolants for the Tokamak reactors. However, alternative coolants should be sought for. As an alternative to liquid metal coolants, molten salts, such as fluorides of lithium and beryllium (so-called FLiBes) or fluorides of alkali metals (so-called FLiNaK) doped with uranium fluoride, can be used. That is why the team of specialists from NRU MPEI and JIHT RAS, in parallel with development of a mercury MHD test facility, is designing a test facility for simulating molten salt heat transfer and hydrodynamics. Since development of this test facility requires numerical predictions and verification of numerical codes, all examined configurations of the MHD flow are also investigated numerically.     

Electron-phonon interaction in short-period (GaAs) m (AlAs) n (001) superlattices

The deformation potentials of electron scattering at short-wavelength phonons for intervalley transitions in the conduction band of short-period (GaAs) _m (AlAs) _n (001) (m, n = 1, 2, 3) superlattices are determined by the electron density functional method. The dependences of the electron and phonon states and deformation potentials on the layer thickness in the superlattices are analyzed. The results of ab initio calculations are in good agreement with the data of empirical calculation of the deformation potentials integrated over phonons, but differ from data on the corresponding potentials for partial scattering channels because of approximations of the phenomenological model of interatomic binding.