Bulletin of the Lebedev Physics Institute最新文献

We examine the main mechanisms limiting the optical power of InGaAsP/InP semiconductor lasers operating at 1.55 μm at high pump currents. Analysis is performed using a numerical calculation of a two-dimensional laser diode model, taking into account transverse drift-diffusion transport and nonuniform distribution of charge carriers and photons along the cavity axis. The calculation results demonstrate the dominant influence of internal losses from scattering by free carriers in the waveguide layer on saturation of the output laser power. As the pump current increases, the primary saturation mechanism becomes leakage current, generated by electron transport into the p-emitter and reducing the internal quantum efficiency. Analysis also shows that the uneven distribution of photons and gain along the cavity axis contributes to the limitation of the output laser power; however, this effect does not significantly affect the primary mechanisms—leakage current and free-carrier losses.

We report the results of studying X-ray emission spectra in the energy range 0.2 keV ≤ hν ≤ 20 keV from the plasma of a laser-induced spark discharge with a current of up to 30 kA. The X-ray energy spectra are measured using an absorber method with a set of lithium fluoride LiF(Mg,Ti) thermoluminescence detectors. X-ray measurements by a pin diode are performed as a supplementary diagnostic. It is shown that the X-ray spectra exhibit noticeable differences at different voltage polarities on high-voltage triggering electrode, with intensity and stability being higher across the entire studied range upon initiation at cathodes.

A compact, all-fiber source of few-cycle pulses at a wavelength of 1.56 μm has been created, based on a two-stage nonlinear amplification scheme in active erbium-doped fibers. Subsequent pulse compression in a silica-glass optical fiber with a large-mode-area (LMA) is demonstrated. The pulse spectrum undergoes coherent broadening due to self-phase modulation sequentially in the first and second amplification stages, based on a highly nonlinear erbium-doped fiber with positive group velocity dispersion. The final pulse compression occurs in a silica-glass LMA fiber with a core diameter of 39 μm, having negative second-order dispersion and lower nonlinearity. The low second-order and third-order dispersion in the active erbium-doped fiber enables effective compression of positively chirped pulses from its output to a duration of 30 fs, corresponding to approximately six wave cycles, in a 10 cm long LMA optical fiber. A maximum compressed pulse energy of 6.3 nJ at an average power of 238 mW is achieved by increasing the pump power of the second amplification stage to 1.2 W, while their peak power is about 100 kW.

We report a computational study of the effect of the initial temperature of the air‒fuel mixture on heat release pulsations during combustion of a pretreated ethane‒air mixture in a model burner device. Combustion processes are modeled using large eddy simulation (LES) with flamelet generated manifolds (FGMs). The amplitude of the air‒fuel mixture velocity pulsations at the inlet is 10%, and the pulsation frequency varies in the range from 150 to 600 Hz. The acoustic response is analyzed using the n‒τ flame model to account for the interaction of the flame front with the acoustic field. As a result, the dependences of heat release pulsations on the velocity pulsation frequency of the supplied mixture are obtained at initial temperatures of 300, 400, and 500 K. It is shown that with a change in the initial temperature of the mixture, the values of the peak frequencies of the pressure pulsations shift upwards by 3‒5%. This means that, for the same flow velocity pulsation frequencies at the inlet, the heat release pulsation amplitudes can vary severalfold with changes in the inlet air temperature.

Numerical modeling tools are more and more valuable due to the availability of high processing power. This study consists of studying the modeling and simulation of a n-V₂O₅ thin film solar cell connected to p-CdTe using the one dimensional PC1D simulation software in a personal computer. In this research, I investigate the impact of different CdTe absorber layer thickness and doping concentration 0.5 to 5 µm and 10¹⁴ to 10²⁰ cm^–3, without a back surface field (BSF) layer. A BSF layer was incorporated in the n-V₂O₅/p-CdTe heterojunction to improve solar cell performance. The influence of the thickness and doping concentration of the Back Surface Field layer (of 0.5–2 µm and 10¹⁴–10²⁰ cm^–3 respectively) was investigated. The highest efficiency of η = 19.7% with J_sc = 27.7 mA/cm², V_oc = 0.807 V, and FF = 88.32% was achieved by the optimal doping concentration and thickness of the p-CdTe and p-ZnTe layers.

The paper describes a method for depositing thin copper films (~0.5‒2.5 μm thick) on Fe, V, and Ti metal surfaces using high-temperature plasma flows. A plasma focus setup with an energy reserve of ~4 kJ is used to generate plasma flows. The elemental composition of Cu films is studied using Rutherford backscattering (RBS) spectrometry. In addition to Cu, the metal surfaces are found to contain C, O, N, and H atoms. It is found that the distribution profiles of these elements and their penetration depth depend on the substrate material: Fe, V, and Ti. The penetration depths of Cu and C atoms for Fe, V, and Ti substrates are ~106, ~120, and ~160 nm and ~150, ~120, and ~200 nm, respectively. A transition layer is found in the initial metal samples: Fe, V, and Ti with a thickness of ~0.01, 0.5, and 0.2 μm, respectively. It occurs after mechanical processing of samples and contains various impurities. An oxide film with a thickness of ~5 nm is found on the surface of the initial metal samples. It is assumed that the oxide film and the transition layer on the metal surface can have a significant effect on the adhesive and electrophysical properties of Cu films. The obtained results are of interest for research on the development of methods for obtaining thin, highly adhesive copper films on the surface of refractory materials. The scope of application of these films includes the production of microchips and electrical contacts, the obtaining of Ti‒Cu alloys for use in biomedical implants, coatings for solar batteries on board spacecraft, and metallization of dielectrics.

The paper describes the observation of a new decay of a beauty baryon using the data collected in CMS experiments in 2016, 2017, and 2018 in proton‒proton collisions at a center-of-mass energy of 13 TeV. The study of the new decay deserves attention because its products contain a charmonium resonance and a doubly strange cascade hyperon, which opens a pathway to the search for new types of pentaquark states. The branching fraction ratio of the new decay to the normalization channel decay is measured.

We report the results of examining the effect of two-photon laser lithography parameters, such as radiation power, lithography speed, and number of repeated exposures per area, on characteristics of the formed features. Analytical relationships are obtained for each parameter. The degree of oligomer conversion as a function of radiation power is analyzed.

A new hodoscopic installation has been built at the Tien Shan Mountain Station to investigate in detail anomalous effects discovered in cosmic rays. It is designed to measure directly the density of muon flux in the core region of extensive air showers (EAS) with a primary energy of 1 to 100 PeV. The new muon hodoscope is based on modern charged particle detectors with a short scintillation flash duration and a high (of the order of several nanoseconds) time resolution of the registration electronics. A specialized program toolchain based on modern machine learning algorithms has been designed for analyzing the acquired information. In addition to investigating the characteristics of the muonic EAS component, the new installation can be used for tasks involving an analysis of the angular distribution of cosmic ray arrival points on the celestial sphere and for selecting showers with reduced hadronic and muonic contents for super-high-energy gamma-ray astronomy.

From the spin dynamics matrix describing the precession of ferromagnetically coupled spins, in a semiinfinite fcc diatomic alloy, we easily access to the localized magnons spectra of the surface of the material. The modeling is carried out by a calculation based on a Heisenberg Hamiltonian with the nearest neighbor interactions and in the presence of the anisotropy term. The localized magnon spectra are calculated and analyzed for different probabilities of the values of the integral exchange and the anisotropy field at the surface of the perfect diatomic alloy waveguide. The simulated cases investigate the magnon modes response to variations in surface parameters (exchange integrals, anisotropy intensity, as well as to the direction of propagation of the exciting spin wave). The numerical results yield an understanding the interference effects between the continuum and the localized spin states on the atomic layers which constitute the surface domain.