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For plasma heating and stabilization in open magnetic traps, the high-power neutral beam injector with tunable beam energy was developed at Budker Institute of Nuclear Physics. The initial energy of the beam particles is 15 keV, and it can be subsequently increased to 40 keV. In this case, the neutral beam power increases from 1.7 to 3.5 MW. A distinctive feature of this injector is the fact that, as the accelerating voltage considerably changes, the ion beam current remains constant. The injectors based on the ion sources with tunable energy are used in experiments at the C-2W open trap (USA).

The spatial and temporal dynamics of the optical loss and carrier density in the heterostructure of a semiconductor laser with a segmented contact are studied using an optical pump–probe technique based on the injection of probe radiation with a wavelength of 1560 nm into a semiconductor laser chip under study that is based on an AlGaAs/InGaAs/GaAs heterostructure and emits at wavelength of 1010 nm. It is demonstrated that employing probe light at a wavelength of 1560 nm enables sensitivity in measuring an internal optical loss of no less than 1 cm–1. The segmented design of the current pumping region made it possible to estimate the absolute internal optical loss. It is shown that changing the configuration of the Fabry–Perot eigenmodes of the laser affects the carrier distribution and the internal optical loss both in the current pumping region and in the passive, current unpumped part of the laser chip.

The emission characteristics of narrow mesa-stripe (5.5 μm) lasers based on asymmetric AlGaAs/GaAs heterostructures are studied. It is shown that the maximum optical power achieved in the continuous-wave (CW) operation mode is limited by heating and reaches a value of 1695 mW at a current of 2350 mA at +25°C, with the maximum efficiency reaching 54.8%. Reducing the working temperature to –8°C makes it possible to raise the maximum low-mode CW power to 2 W. A peak power of 2930 mW is obtained under pumping with current pulses (width 240 ns, amplitude 4230 mA). It is shown that the power profile has in the pulsed mode an “optical dip” region in which low-efficiency lasing occurs with the generation of a train of subnanosecond pulses.

Pulse-pumped MOVPE-fabricated (metal-organic vapor-phase epitaxy) semiconductor lasers emitting in the spectral ranges 1000–1100 and 1400–1600 nm at temperatures of 110–120 K are studied. It is found that cooling the lasers for both spectral ranges to low temperature results in their light–current curves approaching linearity, and an optical power of, respectively, 110 and 20 W can be attained. The low-temperature effect is reduced for lasers emitting in the spectral range 1400–1600 nm. The processes affecting a rise in the internal optical loss in semiconductor lasers are considered. It is shown that an increase in the carrier concentration in the waveguide of a laser structure greatly depends on temperature and is determined by the noninstantaneous capture (capture rate) of carriers from the waveguide into the active region. It is demonstrated that, upon lowering the temperature to 115K, the concentration of electrons and holes in the waveguide becomes lower, which leads to a significant decrease in the internal optical loss and to an increase in the output optical power of the semiconductor laser.

Approaches to the development of laser heterostructures with a broadened single-mode waveguide are studied theoretically and experimentally. It is shown that the use of n- and p-type emitters with different refractive-index values ensures lasing in the fundamental mode only, if the thickness of the waveguide layer is 2 μm. The studied semiconductor lasers fabricated using the developed heterostructure feature internal optical losses amounting to 0.6 cm−1; the divergence in the plane perpendicular to the p-n junction is 23°. In the continuous lasing mode at room temperature, a linear power-current characteristic is obtained at an output optical power as high as 7 W.

Laser heterostructures with waveguides and emitter layers made of AlGaAs and AlGaAsP alloys are grown by hydride metal-organic vapor-phase epitaxy on a GaAs substrate and studied. It was shown that the heterostructure containing AlGaAsP layers has a large curvature radius in comparison with the structure consisting of AlGaAs layers. Ridge waveguide lasers with an aperture of 100 μm are fabricated based on the AlGaAsP/GaAs laser heterostructure and studied. The internal optical loss of the lasers is 0.75 cm−1; the characteristic parameter T0 = 140 K in the temperature range of 20–70°C. The maximum optical output power per mirror reached 4.1 W; cw lasing was retained at a heat sink temperature of 120°C.

Heterostructures with an active region containing a Ga0.59In0.41As quantum well located between GaAs1 − y P y compensating layers were studied using photoluminescence spectroscopy. It was shown that an increase in the phosphorus content in compensating layers makes it possible to obtain unrelaxed heterostructures with wider Ga0.59In0.41As quantum wells. On the basis of photoluminescence studies, the parameters of such a composite active region were chosen with a view to attaining the longest lasing wavelength possible. Laser heterostructures with a composite active region consisting of a highly strained Ga0.59In0.41As quantum well located between GaAs0.85P0.15 compensating layers were grown on GaAs substrates by metalloorganic chemical vapor deposition. Stripe mesa-structure laser diodes of 100-μm aperture emitting at 1220 nm were fabricated. The highest emission power of these laser diodes in the continuous-wave regime amounted to 2 W per output mirror.

Results of photoluminescence (PL) studies of heterostructures with strongly strained InxGa1 − xAs quantum wells (QWs) are presented. It is shown that the dependence of the PL intensity on the QW thickness has a maximum whose position depends on the composition of the InxGa1 − xAs solid solution. The PL wavelength at the maximum intensity is 1.13 µm at a QW thickness of 60 µm at a QW thickness of 50 A for x = 0.39 and 0.42, respectively.

Optical and electrical characteristics of different high-power multimode laser diodes with an emission wavelength of 835 nm are compared; the diodes were obtained on the basis of three systems of solid solutions: AlGaAS/GaAs, AlGaAs/GaAsP, and (Al)GaInP/GaInAsP. An output continuous optical power of 5 W is attained in lasers with a stripe width of 80 μm irrespective of the chosen material system. The highest optical power, 7 W, is attained in the lasers based on the (Al)GaInP/GaInAsP system.

The parameters of high-power multimode laser diodes featuring a radiation wavelength of 808 nm obtained on the basis of asymmetric heterostructures with an ultrawide waveguide in the systems of AlGaAs/GaAs and (Al)GaInP/GaInAsP/GaAs are compared. In the lasers based on an AlGaAs/GaAs system, the maximum optical power was limited by optical degradation of the SiO2/Si mirrors and amounted to 4.7 W. In the lasers based on an (Al)GaInP/GaInAsP/GaAs system, the maximum optical power was limited by thermal saturation and equaled 7 W. The obtained results show that the (Al)GaInP/GaInAsP/GaAs system is more reliable from the standpoint of an increase in both the maximum optical power and operation life of lasers.

Spectral and emission-power characteristics of semiconductor lasers based on quantum-dimensional asymmetric heterostructures with separate confinement in a system of InGaAs/GaAs/AlGaAs alloys are studied in the case of high pump levels in the pulsed mode of lasing (200 A, 100 ns, and 10 kHz). It is shown that, in lasers with a quantum-dimensional active region containing one or two levels of dimensional quantization, the spectrum consists of one or two lasing bands. It is established that the condition for inverse population of the second electron level and two-band lasing are attained due to leveling-off of the rate of stimulated recombination from the first electron level and a high density of states for the second level. It is shown that, in lasers with double-band lasing spectrum, the total emission spectrum exceeds appreciably the emission power of a laser with a single electron level and a single spectral band.

Spectral and light-current characteristics of separate-confinement lasers that are based on InAl-GaAs/InP and InGaAsP/InP alloys and emit in the wavelength range of 1.5–1.8 μm are studied at high excitation levels (up to 80 kA/cm2) in pulse operation (100 ns, 10 kHz). It is shown that the peak intensity in the stimulated-emission spectrum saturates as the pump current is increased. Further increase in the emitted power is attained owing to the emission-spectrum broadening to shorter wavelengths, similar to lasers on the GaAs substrates (λ = 1.04 μm). It is established experimentally that the broadening of the stimulated-emission spectrum to shorter wavelengths is caused by an increase in the threshold current and by an increase in the charge-carrier concentration in the active region. This concentration increases by a factor of 6–7 beyond the lasing threshold and can be as high as 1019 cm−3 in pulse operation. It is shown that saturation of the light-current characteristics in pulse operation takes place in the InAlGaAs/InP and InGaAsP/InP lasers as the pump current is increased. It is shown experimentally that there is a correlation between saturation of the light-current characteristic and an increase in the threshold current in the active region. An increase in the charge-carrier concentration and gradual filling of the active region and waveguide layers with electrons are observed as the pump current is increased; stimulated emission from the waveguide is observed at high pump currents.

Asymmetric GaInAs/GaInAsP/AlGaAs heterostructures with the emission wavelength of 940 and 980 nm were grown by MOCVD. The composition of solid solution in the waveguide layer, Ga0.74In0.26As0.47P0.53, was chosen based on the calculations of the escape energy of electrons from the quantum well of the active region into the waveguide. Semiconductor lasers with the emission aperture of 100 μm were fabricated from these heterostructures. The CW output optical power of 12 W was achieved at room temperature. The internal optical loss was 0.6 and 0.3 cm−1 for 940 and 980 nm wavelengths, respectively.

Asymmetric separate-confinement laser heterostructures with ultrawide waveguides based on AlGaAs/GaAs/InGaAs solid solutions, with an emission wavelength of ∼1080 nm, are grown by MOCVD. The optical and electrical properties of mesa-stripe lasers with a stripe width of ∼100 μm are studied. Lasers based on asymmetric heterostructures with ultrawide (>1 μm) waveguides demonstrate lasing in the fundamental transverse mode with an internal optical loss of as low as 0.34 cm−1. In laser diodes with a cavity length of more than 3 mm, the thermal resistance is reduced to 2°C/W, and the characteristic temperature T 0= 10°C is obtained in the range 0–100°C. A record-breaking wallplug efficiency of 74% and an output optical power of 16 W are reached in CW mode. Mean-time-between-failures testing for 1000 h at 65°C with an operation power of 3–4 W results in the power decreasing by 3–7%.

Metal-organic chemical vapor deposition (MOCVD) was used to form laser heterostructures in the system of GaInAsP/GaInP/AlGaInP solid solutions. The design of the laser structure was chosen on the basis of the calculated band offsets at the heteroboundaries in the active region of the waveguide. A maximal optical power of 320 mW is attained at the output of the mesa-stripe diode laser with a stripe width of W=5 µm in continuous-wave mode at 780 nm.

Optical and structural properties of InGaAsP solid solutions grown by MOVPE at 600°C on GaAs(001) substrates are studied. The photoluminescence spectra of InGaAsP solid solutions with a composition corresponding to the miscibility gap contain a main band and an additional auxiliary band. It is established that both bands are related to band-to-band radiative transitions; i. e., the studied layer includes two solid solutions with different compositions and different band gaps. It is shown that the observed high-energy shift of the additional band with an increasing level of excitation is governed by the nanometer size of domains in the corresponding solid solution. This conclusion is consistent with the results of TEM study, which revealed the presence of a periodic structure comprised of alternating domains with different compositions. This structure of alternating domains extends along the [100] and [010] directions with a characteristic period of 10 nm.

Carbon doping of GaAs and AlGaAs layers grown by low-pressure metalorganic chemical vapor deposition, using triethylgallium, trimethylaluminum and arsine as growth precursors and carbon tetrachloride as dopant precursor, were investigated. Doping level dependence on growth temperature, growth rate, V/III ratio and AlAs mole fraction was established. InGaAs/AlGaAs DQW broad waveguide separate confinement laser heterostructures with different p-clad doping have been studied. Heterostructures design and optimization of active area growth conditions have been fulfilled to obtain high-power operation of laser diodes (LDs) with low transverse divergence. Carbon tetrachloride and diethylzinc were used as p-type dopant precursors. There were investigated three types of heterostructures: (a) C-doped AlGaAs p-clad and heavy C-doped GaAs contact layer, (b) C-doped AlGaAs p-clad and heavy Zn-doped GaAs contact layer, (c) Zn-doped AlGaAs p-clad and heavy Zn-doped GaAs contact layer. Broad area LDs were manufactured and analyzed. As a result the optimal p-type dopant precursor for high-power LDs was discussed.

A metal-organic chemical vapor deposition (MOCVD) technique is developed for a diode laser heterostructure in a system of InGaAs/GaAs/AlGaAs solid solutions; the optimal sizes and the doping profile of the structure are determined to minimize the internal optical losses. Mesa-strip diode lasers with a threshold density of current Jth=150–200 A/cm2, internal optical loss factor αi=1.6–1.9 cm−1, and an internal quantum yield ηi=85–95% were fabricated. In the continuous lasing mode of a diode laser with a 100-µm-wide aperture and a wavelength of 0.98 µm, the optical power output was as high as 6.5 W and was limited by the catastrophic optical degradation of mirrors. The radiation divergence in the plane normal to the p-n junction amounts to θ⊥. The use of wide-gap waveguide layers, which deepens the potential electron well in the active region, is shown to reduce the temperature sensitivity of the InGaAs/GaAs/AlGaAs laser heterostructures in the temperature range from 0 to 70°C.

A MOCVD technology for growth of InGaAs/GaAs/InGaP laser heterostructures on a modified Epiquip VP-50-RP installation was developed. Mesa stripe laser diodes with threshold current density Jth=100–200 A/cm2, internal optical loss αi=1.3–1.7 cm−1, and internal quantum efficiency ηi=60–70% have been fabricated. A CW output optical power of 5 W has been obtained for a single 100-µm-wide aperture mesa stripe laser diode emitting at 1.03 µm. It is shown that use of AlGaAs waveguide layers, which increase the conduction band barrier offset, lowers the temperature sensitivity of laser heterostructures within the temperature range 10–80°C.

Continuous-wave output powers of 9.2 W at a constant heatsink temperature of 10°C and 12.2 W at a stabilized temperature of the active region have been obtained on an InGaAs/AlGaAs laser with a 0.4-µm-thick waveguide, operating at 1.03 µm. Record-breaking output mirror power densities of, respectively, 29.9 and 40 MW/cm2 have been achieved without catastrophic optical mirror damage in the two temperature-stabilization regimes. A maximum power conversion efficiency of 66% has been achieved in a laser with a cavity length of 2 mm.

Liquid-phase epitaxy of InGaAsP solid solutions isoperiodic with (001)GaAs substrates was studied in the miscibility gap. At the initial stage of deposition (first 1–2 s), thin (up to 0.15 µm) planar layers of homogeneous InGaAsP solid solutions are formed. This is aided by pronounced supercooling of the melt (by 10–15°C) and the resulting high growth rates. In further stages, growth becomes slower and a natural nanoheterostructure starts to form owing to decomposition of the solid solution. The formation of a nanoheterostructure comprising domains of different compositions with different lattice constants is accompanied by the appearance of an undulating relief on the sample surface, with the undulation magnitude increasing as the layer grows. Under the technological conditions employed, the thickness of InGaAsP solid solution layers containing a nanoheterostructure is limited to 0.5 µm.

The paper is concerned with the application of path integration (successive integration over “fast” and “slow” variables and the Hubbard-Stratonovich transformation) to the antiferromagnetic state in the three-band, two-dimensional repulsive Hubbard model. It is shown that, in the lowest approximation, the model under consideration is equivalent to the half-filled single-band Hubbard model. The effective action for the collective Bose-fields, the critical temperature of the phase transition, and the spectra of excitations are obtained. Bibliography: 24 titles.

Photoluminescence and electroluminescence techniques were used to study spontaneously forming periodic InGaAsP structures that consisted of two types of alternating solid-solution domains differing in composition and lattice constant. It was found experimentally that the volume of the narrow-gap material domains is smaller than that of the wide-gap domains. Existence of the inelastic strain caused by the large (2–3%) lattice constant mismatch between the adjacent domains was inferred. Laser diodes with the spontaneously forming periodic InGaAsP structures in the active region were fabricated, and lasing in the long-wavelength electroluminescence spectral band that originated from the radiative recombination in the narrow-gap domains was obtained. Lasing at the threshold current densities of 70 A/cm2 at 77 K and 700 A/cm2 at 300 K was observed in the highest-quality samples.

Arrays of strained nanoscale InP islands in an In0.49Ga0.51P host on a GaAs(100) substrate and InAs islands in a In0.53Ga0.47As host on an InP(100) substrate are obtained by metalorganic vapor-phase epitaxy (MOVPE). Their structural and photoluminescence properties are investigated. It is shown that the nanoscale islands that are formed measure 80 nm (InP/InGaP) and 25–60 nm (InAs/InGaAs). The photoluminescence spectra of the nanoscale islands display bands in the wavelength ranges 0.66–0.72 and 1.66–1.91 µm at 77 K with maxima whose position does not vary as the effective thickness of InP and InAs increases. The radiation efficiency of the nanoscale InP islands is two orders of magnitude greater than the luminescence intensity of the InAs islands.

This paper discusses the photoluminescence and x-ray microstructural properties of epitaxial layers of solid solutions of InGaAsP isoperiodic with InP (100) and GaAs (100) substrates, obtained in the region of immiscibility and spinodal decay. It shows that there is good agreement of the experimental results with the theoretical model of spinodal decay. The boundaries of the region in which two solid phases of different composition exist in epitaxial layers of solid solutions of InGaAsP isoperiodic with the InP and GaAs substrates are determined. A periodic nanoheterostructure is obtained in an epitaxial layer of InGaAsP solid solutions with a repetition period of 650±30 A in two mutually perpendicular directions.

The spectrum of collective modes in the antiferromagnetic state of the two-dimensional weakly repulsive Hubbard model is calculated by means of path integration with the use of “fast” and “slow” variables and the Hubbard-Stratonovich transformation both in the Ginzburg-Landau region and near zero temperature.

A method of taking account of the strong Coulomb correlations for the Kondo-lattice model is suggested. The elementary excitations and phase transitions in this model for the CuO2 layers in the superconducting oxides are investigated by this method. Bibliography: 12 titles.

Photoluminescence (PL) of n-InN grown by molecular beam epitaxy with Hall concentrations from 3.6 to 7.3 × 1017 cm–3 demonstrates dependences on carrier concentration, temperature, and excitation density which give evidences of a fast energy relaxation rate of photoholes and their equilibrium distribution over localized states. The structure of the PL spectra observed at 4.2 and 77 K in the energy interval from 0.50 to 0.67 eV indicates that a considerable part of holes is trapped by deep and shallow acceptors before the interband recombi- nation with degenerate electrons occurs. At room temperature, the band-to-band recombination of free holes and electrons dominates in PL. Experimental results on PL and absorption are described by model calculations under the assumptions of a band gap equal to 0.665–0.670 eV at zero temperature and zero carrier concentration and a non-parabolic conduction band with the effective mass at the G-point equal to 0.07 of the free electron mass. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We represent the partition function of the Hubbard model with a strong Coulomb repulsion as a path integral over auxiliary Grassman variables. An approximate analysis of the phase transitions demonstrates that (1) the system is an antiferromagnetic insulator when the doping constant δ is small, (2) when δ ⩾ t/U, the system is a ferromagnetic metal if U/t > 10, and a superconducting metal if U/t ≲ 10.

Results of photoluminescence (PL) studies of self-organized nanoscale InP islands (quantum dots, QDs) in the In0.49Ga0.51P matrix, grown on a GaAs substrate by metalorganic vapor phase epitaxy (MOVPE), are presented. Dependences of the PL efficiency on temperature in the range 77–300 K and on excitation level at pumping power densities of 0.01–5 kW/cm2 have been obtained. The PL spectra are a superposition of emission peaks from QDs and the wetting layer. Their intensity ratio depends on the pumping power and temperature, and the emission wavelength varies in the range 0.65–0.73 µm. At 77 K and low excitation level, InP QDs exhibit high temperature stability of the emission wavelength and high quantum efficiency.

The modified “slave-boson” method is used to describe the metal-insulator and metal-superconductor phase transitions in the Hubbard model. Expressions are derived for the energy gap and phase-transition temperature.

It is established theoretically and experimentally that in certain temperature and composition ranges the solid solutions InGaAsP comprise a system of strained, alternating (in mutually perpendicular directions [100] and [010]) domains of a solid solution with two different compositions and different lattice constants. The domains are clearly seen at the surface of an epitaxial film and wash out into its depth in the direction of the substrate. The data obtained most likely show spinodal decomposition of InGaAsP solid solutions in the experimental samples.

Abrasive cutting wheels reinforced with silicon carbide fibers are produced and tested. Their wear resistance for cutting steel pipes is much greater than in commercially produced wheels reinforced by glass network. The use of silicon carbide fibers makes it possible to produce wheels 1.0–1.5 mm in thickness while analogous commercial wheels are only 3.0 mm in thickness. Decreasing the thickness of the wheel helps save a scarce material, reduces the power rating of the equipment, and decreases the width of the cut.

Measurements are conducted of the Kerr constant of ultrapure water with resistivity 107 Ω · cm. Values of the Kerr constant of (3.26 ± 0.10) · 10-7 and (2.29 ± 0.07) · 10-7 esu were obtained at a temperature of 30 °C for wavelengths of 441.6 nm and 632.8 nm.

The thermal conductivity of lithium vapor is measured. Equations are derived for calculation of the effective thermal conductivity and its components over a wide range of temperature and pressure.

New results are presented on studying the beam-plasma interaction and plasma heating dynamics at the INAR device. The specific features of the generation of 'hot' (E>approximately 1keV) plasma electrons containing the main part of the plasma energy are studied. In the case of a beam with a small initial angular spread, the 'hot' electrons are mainly generated near the point where the beam is injected into the plasma. Also reported are the results of the experiments in which the magnetic field in the beam-plasma interaction region was increased up to 70 kOe. In this case, at the plasma length of 75 cm, the total beam energy losses exceed 40%. The growth of the plasma energy content at higher magnetic field is observed. The first stage of the GOL-3 experiment is described which is aimed at the study of the plasma heating of a solenoid by a 100 kJ microsecond electron beam. This experimental device is ready for operation.

We consider the phenomenon of localized superconductivity (LS), the local raising of temperature of superconductivity transition near a planar imperfection and the surface of a metal. We find a condition for the existence of LS depending on the density of the states on the Fermi surface. We show that the presence of Tamm states is sufficient for LS to occur.

A self-consistent field equation obtained by the method of functional integration is applied to investigate the structure of the lattice near the surface of a simple metal. Formulas are obtained for the displacements of ions relative to the nodes of an ideal lattice near the surface of the metal. Formulas are presented for the surface potential and the work of exit for one-dimensional and three-dimensional models.

The potential of the effective interaction between electrons in a thin layer around the Fermi surface is derived by the functional integration method. A condition for the attraction between electrons is established in the statical limit.

The experimental excitation of intense collisionless shock waves (M ≥ 5) with subsequent plasma compression by the magnetic field of a shock coil is described. A magnetic plug > 20 kOe is produced in ≈ 100 × 10−9 sec by a current generator, a long line with 250-kV water insulation and a characteristic impedance of l Ω At an initial deuterium-plasma density of ≈ 2 × 1014 cm−3, shock waves with a front width of ≈ 20c/ω03and a velocity of ≈ 5 × 107 cm/sec are recorded. The ion energy after the accumulation, determined from the neutron yield, turns out to be ≥ 2 ke V. Axial shock waves excited by the plasma flow beneath the shock coil are observed.