Showing papers in "Technical Physics Letters in 1999"
TL;DR: In this article, the operation of cold explosive-emission cathodes having a current density of ∼104 A/cm2, fabricated using various materials, was investigated under a large number of switching cycles.
Abstract: The operation of cold explosive-emission cathodes having a current density of ∼104 A/cm2, fabricated using various materials, was investigated under a large number of switching cycles. The cathode voltage was ∼500 kV, the maximum current ∼5 kA, and the pulse duration ∼20 ns. It is shown that when the number of switchings is small (⩽103 pulses), cathodes having similar geometry exhibit similar emission properties. For most of the materials studied, as the number of switching cycles increases (⩾103 pulses), the current rise time increases (as far as the pulse duration) and the maximum vacuum diode current decreases. When a graphite cathode was used, the maximum current remained unchanged up to 108 switching cycles. The mass removed from the cathode was determined for various materials. The results were used to achieve continuous operation of a relativistic 3 cm backward-wave tube having an output power of 350–400MW and an almost constant power level during 108 pulses at a repetition frequency of 100–150 Hz.
31 citations
TL;DR: In this paper, high-temperature superconducting Josephson junctions on bicrystal sapphire substrates were fabricated and investigated experimentally, and the critical parameters of the junctions satisfy the constraints for the design of devices in the millimeter and submillimeter wavelength ranges.
Abstract: High-temperature superconducting Josephson junctions on bicrystal sapphire substrates were fabricated and investigated experimentally. The critical parameters of the junctions satisfy the constraints for the design of devices in the millimeter and submillimeter wavelength ranges. The results of dynamic measurements show that in these junctions the superconducting current exhibits a sinusoidal dependence on the phase difference of the superconducting wave functions of the electrodes, and a simple resistive model is used to analyze their microwave properties. At the same time, the temperature dependence of the critical current of the junctions differs appreciably from that typical of tunnel junctions with s-superconductors and may be explained as d-type pairing of the superconducting electrodes and an SNS junction.
24 citations
TL;DR: In this paper, a new highly selective Bragg cavity system having phase discontinuity in the ripples inside the interaction space was used to develop a free-electron maser based on the LIU-3000 accelerator.
Abstract: A new, highly selective Bragg cavity system having phase discontinuity in the ripples inside the interaction space was used to develop a free-electron maser based on the LIU-3000 accelerator (free-electron maser oscillator). This system operated at 30.7 GHz with a power of around 50MW and an efficiency of 35%, which is the highest yet recorded for this class of system.
24 citations
TL;DR: In this article, an experimental investigation was made of x-ray bremsstrahlung in the 2-10 keV range of a pulsed discharge under electron cyclotron resonance conditions in a straight magnetic mirror system pumped by a high-power millimeter radiation beam.
Abstract: An experimental investigation is made of x-ray bremsstrahlung in the 2–10 keV range of a pulsed discharge under electron cyclotron resonance conditions in a straight magnetic mirror system pumped by a high-power millimeter radiation beam. The plasma temperature and density were determined from the spectrum and intensity of the x-rays. The results indicate that a quasi-gasdynamic plasma confinement regime is achieved.
22 citations
TL;DR: In this paper, the condition for self-reproduction of multimode Hermite-Gaussian beams is analyzed and a numerical example is presented, where the condition is based on the condition of the Hermite Gaussian beam.
Abstract: The condition for the self-reproduction of multimode Hermite-Gaussian beams is obtained and analyzed. Partial self-reproduction planes are also considered. A numerical example is presented.
21 citations
TL;DR: In this paper, the epitaxial layers of InGaAs solid solutions were grown on porous GaAs(100) substrates by liquid-phase epitaxy, and a comparison between the compositions and thicknesses of these layers with those of layers obtained under the same conditions on normal monolithic GaAs substrates was made.
Abstract: Epitaxial layers of InGaAs solid solutions were grown on porous GaAs(100) substrates by liquid-phase epitaxy. A comparison between the compositions and thicknesses of these epitaxial layers with those of layers obtained under the same conditions on normal monolithic GaAs substrates suggests that the crystallization of epitaxial layers on porous substrates may be considered as the growth of free unstrained films.
21 citations
TL;DR: The breakdown velocity increases to 10−20 cm/ns when the leading edge of the negative voltage pulse decreases to 0.5−2.5 ns as discussed by the authors, which can be explained by the appearance of a short-pulse beam of high-energy electrons which produce in the gap a sufficient number of initial electrons.
Abstract: The breakdown velocity increases to 10–20 cm/ns when the leading edge of the negative voltage pulse decreases to 0.5–2.5 ns. The sharp increase in the velocity can be explained by the appearance of a short-pulse beam of high-energy electrons which produce in the gap a sufficient number of initial electrons.
20 citations
TL;DR: In this paper, it was shown experimentally and theoretically that when an optical vortex propagates in free space, its wavefront rotates through an angle numerically equal to the Gouy phase, and that both the energy maximum of the optical vortex light flux and the amplitude zero of the perturbed optical vortex field propagate along the ray surface.
Abstract: It is shown experimentally and theoretically that when an optical vortex propagates in free space, its wavefront rotates through an angle numerically equal to the Gouy phase. It is found that both the energy maximum of the optical vortex light flux and the amplitude zero of the perturbed optical vortex field propagate along the ray surface. It is shown that the ray surface, which is a consequence of the relativistic constraints on the beam group velocity, forms an unparted hyperboloid of revolution and has various properties: 1) the circulation of the Poynting vector on the surface does not depend on the longitudinal coordinate z; 2) the evolution of the light flux and a pure screw dislocation takes place along straight lines of this surface; 3) the Poynting vector on the ray surface is always perpendicular to the wavefront surface.
19 citations
TL;DR: In this paper, the experimental confirmation of the existence of the electrostriction mechanism of microwave losses in a thin ferroelectric film is discussed and the results of simulation of the dielectric loss tangent due to the mechanism discussed for a planar capacitor with one gap are compared with existing experimental data for an interdigital capacitor.
Abstract: The experimental confirmation of the existence of the electrostriction mechanism of microwave losses in a thin ferroelectric film is discussed. The results of simulation of the dielectric loss tangent due to the mechanism discussed for a planar capacitor with one gap are presented and compared with existing experimental data for an interdigital capacitor. The simulation results agree well with the experimental data. The small discrepancy with experiment could be due to inaccurate determination of the sound velocity in the ferroelectric film and to differences in the capacitor structures used in the simulation and in the experiment.
19 citations
TL;DR: In this paper, a study was made of the possibility of using fullerene-containing polymers as materials for gas-separating membranes and a correlation was established between the change in the transport properties and the free volume.
Abstract: A study is made of the possibility of using fullerene-containing polymers as materials for gas-separating membranes. Fullerene-containing poly(phenylene oxide) was prepared and its density and free volume were estimated. The coefficients of gas permeability and the selectivity factors for separation of air into oxygen and nitrogen were measured for poly(phenylene oxide) having various fullerene contents. A correlation is established between the change in the transport properties and the free volume. It is shown that modifying poly(phenylene oxide) with fullerene is potentially useful for improving the transport properties of the membranes.
18 citations
TL;DR: In this paper, an analysis of the equilibrium profile of the free surface of a liquid metal in an external electric field neglecting gravitational forces is made, and it is shown that a conformal mapping method can be used to find a wide range of exact solutions corresponding to the case of planar symmetry.
Abstract: An analysis is made of the equilibrium profile of the free surface of a liquid metal in an external electric field neglecting gravitational forces. It is shown that a conformal mapping method can be used to find a wide range of exact solutions corresponding to the case of planar symmetry.
TL;DR: In this article, it was shown that InN and GaN whiskers and plate-shaped crystals can be grown by molecular-beam epitaxy (MBE), and the growth mechanism on gallium arsenide and sapphire substrates was investigated.
Abstract: It is shown that InN and GaN whiskers and plate-shaped crystals can be grown by molecular-beam epitaxy (MBE), and the growth mechanism on gallium arsenide and sapphire substrates is investigated. A comparison is made with the theory. It is proved that the growth mechanism corresponds to the vapor-liquid-solid (VLS) mechanism, and the parameters of the crystallization process are determined. The nanometer sizes of the crystals grown give hope that the crystals and the VLS growth method itself can be used to obtain quantum-size objects (quantum dots and wires) by MBE in the promising system of elements A3B5-AlGaInN.
TL;DR: In this article, a glow discharge in a mixture of argon and hydroxyl (OH) was investigated experimentally and it was shown that under certain discharge conditions a considerable portion of the electrical energy imparted to the discharge is used to generate resonant emission of OH molecules.
Abstract: A glow discharge in a mixture of argon and hydroxyl (OH) is investigated experimentally. It is shown that under certain discharge conditions a considerable portion of the electrical energy imparted to the discharge is used to generate resonant emission of OH molecules. The results obtained point to a realistic possibility of creating a new, ecologically friendly source of optical radiation, which can replace mercury lamps in the near future.
TL;DR: In this paper, it was shown that GaN layers can be grown on (100)-and (111)-oriented porous single-crystal GaAs substrates by molecular-beam epitaxy with plasma activation of the nitrogen by an rf electron cyclotron resonance discharge.
Abstract: It is shown that GaN layers can be grown on (100)-and (111)-oriented porous single-crystal GaAs substrates by molecular-beam epitaxy with plasma activation of the nitrogen by an rf electron cyclotron resonance discharge. The resulting undoped epitaxial layers possessed ntype conductivity with a carrier concentration ∼1018. Data obtained by scanning electron microscopy and cathodoluminescence indicate that at thicknesses ∼2000 A, continuous layers of the cubic GaN modification are obtained regardless of the substrate orientation.
TL;DR: In this paper, an experimental investigation was made of the possibility of developing a new efficient gas-discharge source of optical radiation based on an OH hydroxyl molecular additive, and it was shown that under certain discharge conditions, the luminous efficiency of a positive discharge column in a rare gas-hydroxyl mixture is similar to that of a mercury discharge.
Abstract: An experimental investigation was made of the possibility of developing a new efficient gas-discharge source of optical radiation based on an OH hydroxyl molecular additive. It is shown that under certain discharge conditions, the luminous efficiency of a positive discharge column in a rare gas-hydroxyl mixture is similar to that of a mercury discharge. The results suggest that it may be possible to develop a new ecologically innocuous source of optical radiation which may in future replace mercury luminescence light sources.
TL;DR: A theoretical and experimental investigation of the magnitude and nature of dielectric losses in weakly absorbing synthetic diamonds in the wavelength range 1.75-6.8 mm at temperatures T=20-500 °C was made in this paper.
Abstract: A theoretical and experimental investigation is made of the magnitude and nature of the dielectric losses in weakly absorbing synthetic diamonds in the wavelength range 1.75–6.8 mm at temperatures T=20–500 °C. Some samples exhibited extremely low losses (tan δ <10−5) which makes plasma-chemically deposited diamond wafers suitable for fabricating windows for megawatt continuous gyrotrons. It is shown that in principle, a further substantial reduction in losses can be achieved.
TL;DR: In this paper, it is suggested that nitrogen may be used as the ambient medium to obtain highly dispersed powders of pure metals, and a reduction in the gas density reduces the particle size of the pure metal powder down to the nanometer range.
Abstract: It is suggested that nitrogen may be used as the ambient medium to obtain highly dispersed powders of pure metals. At reduced pressure nitrogen is chemically inert and has a higher dielectric strength than rare gases. A reduction in the gas density reduces the particle size of the pure metal powder down to the nanometer range.
TL;DR: In this paper, the photoelectric properties of In2O3-GaTe and GaTe-InSe heterojunctions were investigated using a diffusion model of the heterojunction.
Abstract: The photoelectric properties of In2O3-GaTe and GaTe-InSe heterojunctions were investigated. Their characteristics were described using a diffusion model of the heterojunction. Some deviation of the characteristics from ideal was observed for In2O3-GaTe heterojunctions as a result of the presence of a thin dielectric layer at the heteroboundary. Qualitative energy band diagrams were constructed for the heterojunction and their photosensitivity was determined in the range 0.33–1.0 μm.
TL;DR: In this paper, the Keating model was used to calculate the elastic constants of GaN and AlN for sphalerite and wurtzite structures for cubic gallium and aluminum nitride: C11=325 and 322, C12=142 and 156, C44=147 and 138.
Abstract: The Keating model is used to calculate the elastic constants of GaN and AlN for sphalerite and wurtzite structures. The following values of the elastic constants (in gigapascals) were obtained for cubic gallium and aluminum nitride: C11=325 and 322, C12=142 and 156, C44=147 and 138.
TL;DR: In this paper, a numerical simulation is used to investigate the dynamics of positive streamers in liquid argon and it is shown that as in gases, the nature of the streamer propagation depends on the field strength in the discharge gap.
Abstract: A numerical simulation is used to investigate the dynamics of positive streamers in liquid argon. It is shown that as in gases, the nature of the streamer propagation depends on the field strength in the discharge gap. It is established that electron-ion recombination in the streamer channel plays a significant role compared with streamers in gases.
TL;DR: In this article, an analysis is made of the possibility of solving the inverse problem of reconstructing the internal structure of an object using a set of experimental distributions measured in an x-ray beam for various orientations of the object.
Abstract: An analysis is made of the possibility of solving the inverse problem of reconstructing the internal structure of an object using a set of experimental distributions measured in an x-ray beam for various orientations of the object.
TL;DR: In this paper, it was shown that for a symmetric definition of the transport current across the junction with an edge transparency of the order of 10 − 4 and a mirror-symmetric bicrystal interface, the current-phase dependence is close to sinusoidal.
Abstract: Dependences of the amplitudes of the harmonic and subharmonic Shapiro steps on an external monochromatic signal were used to study the current-phase dependence of high-temperature superconducting junctions on a bicrystal substrate. It is shown that for a symmetric definition of the transport current across the junction with an edge transparency of the order of \(\bar D = 10^{ - 4}\) and a mirror-symmetric bicrystal interface, the current-phase dependence is close to sinusoidal which differs from the theoretical predictions and is most likely caused by twinning of the high-temperature superconducting films of the electrodes forming the junction. A departure from symmetry in the definition of the transport current across the junction causes the current-phase dependence to deviate from sinusoidal, which increases with increasing degree of asymmetry. This change in the current-phase dependence is accurately described by a model which takes into account the formation of coupled Andreev states in junctions of superconductors with a \(d_{x^2 - y^2 } \) type of superconducting wave function.
TL;DR: In this paper, specific characteristics of the amplification of short electromagnetic pulses propagating along a steady-state nonequilibrium electron beam whose group velocity differs from the particle translational velocity are studied.
Abstract: Specific characteristics of the amplification of short electromagnetic pulses propagating along a steady-state nonequilibrium electron beam whose group velocity differs from the particle translational velocity are studied. It is shown that as a result of one of the pulse leading edges being continuously supplied with electrons having no initial modulation, a high level of amplitude is achieved, substantially exceeding the saturation level for the amplification of quasisteady-state signals.
TL;DR: In this article, an optoelectronic neural system for processing the output data from a distributed fiber-optic tomographic-type measuring network is reported, in which the interneuron coupling matrix is implemented using a collection of amplitude holograms recorded on a diskshaped holographic carrier.
Abstract: The results of an investigation of an optoelectronic neural system for processing the output data from a distributed fiber-optic tomographic-type measuring network are reported. The processing system is based on the operation principle of an optical perceptron in which the interneuron coupling matrix is implemented using a collection of amplitude holograms recorded on a disk-shaped holographic carrier. It is shown experimentally that this system makes it possible to reconstruct to within 20% the spatial distribution functions of the physical quantity under investigation.
TL;DR: In this article, the influence of microwave irradiation on the low-frequency current-voltage characteristics of p-n junction diodes was investigated and it was shown that when the microwave power increases to a certain level, a clearly defined S-shaped section appears on the currentvoltage characteristic of the diode.
Abstract: An experimental investigation was made of the influence of microwave irradiation on the low-frequency current-voltage characteristics of p-n junction diodes. It is shown that when the microwave power increases to a certain level, a clearly defined S-shaped section appears on the current-voltage characteristic of the diode. This section becomes broader as the microwave signal increases further and then disappears when the microwave irradiation ceases.
TL;DR: In this article, the effect of the ratios of the cationic components and internal strains on the critical temperature T c and the dielectric characteristics of BSTO ferroelectric films grown on α-Al2O3 and LaAlO3 substrates was investigated.
Abstract: The effect of the ratios of the cationic components and internal strains on the critical temperature T
c
and the dielectric characteristics of BSTO ferroelectric films grown on α-Al2O3 [1012] and LaAlO3 substrates were investigated. Ion backscattering diagnostics revealed a barium deficiency in the surface layer of the films and showed that the films differ in structural quality.
TL;DR: In this article, the development of sealed XeCl, KrCl and XeI excilamps excited by a capacitive rf discharge was reported, and an average emission power of 3W was obtained with a ∼12% efficiency.
Abstract: The development of sealed XeCl (λ∼308 nm), KrCl (λ∼222 nm), and XeI (λ∼253 nm) excilamps excited by a capacitive rf discharge is reported. It is shown that highly efficient emission of exciplex molecules is achieved under capacitive discharge excitation and the emitter has a simple design. An average emission power of 3W was obtained with a ∼12% efficiency and the lifetime of the sealed excilamps was longer than 1000 h.
TL;DR: In this paper, the absorption spectra of a single-crystal La0.35Pr 0.35Ca0.3MnO3 film were studied in the spectral range 0.1-1.6 eV at temperatures between 80 and 295 K.
Abstract: The absorption spectra of a single-crystal La0.35Pr0.35Ca0.3MnO3 film were studied in the spectral range 0.1–1.6 eV at temperatures between 80 and 295 K. The metal-insulator transition in the temperature range 160–180K was accompanied by an abrupt increase in the intensity of the transmitted light by a factor of ∼400. An applied magnetic field of 0.8 T causes a 55% relative change in the intensity near the transition. The prospects for using these effects to create magnetically controlled optical devices are considered.
TL;DR: In this article, it is shown that the use of a strontium titanate sublayer can ensure that the dielectric properties of barium strontia titanate films have a weak temperature dependence over a wide temperature range, which is consistent with those required to fabricate microwave microelectronics devices.
Abstract: Results are presented of experiments to deposit barium strontium titanate films on an r-cut sapphire substrate with a strontium titanate sublayer. It is shown that the use of a strontium titanate sublayer can ensure that the dielectric properties of barium strontium titanate films have a weak temperature dependence over a wide temperature range. Moreover, the parameters of the films are consistent with those required to fabricate microwave microelectronics devices.
TL;DR: In this article, the synthesis of layers of glycerin-containing, self-developing bichromated gelatin between 100 and 500 μm thick is described and the holographic characteristics of this light-sensitive material are discussed.
Abstract: The synthesis of layers of glycerin-containing, self-developing bichromated gelatin between 100 and 500 μm thick is described and the holographic characteristics of this light-sensitive material are discussed. Experimental data obtained by measuring the diffraction efficiency of holograms of two plane waves recorded using a symmetric system for layers of different thickness and various ammonium bichromate concentrations showed that the optimum layers for hologram recording are around 200 μm thick and have an ammonium bichromate concentration of 2–2.5% by weight of dry gelatin. The sensitivity of these layers is 5–10 J/cm2.