JETP Letters最新文献

The spectrum of inelastic collisions of low-energy protons in the field of molecular excitations of water is obtained in terms of the complex refractive index of water determined from optical measurements in the infrared, visible, and ultraviolet regions. In the range of atomic frequencies (energies), the inelastic collision spectrum is determined from the integrated absorption cross section of X and gamma rays. The resulting spectra will extend the range of applicability of the photoionization model, which is of interest for improving dosimetry planning of the exposure of patients in proton (ion) therapy.

The long-term relaxation dynamics of neutral excitations with spin 1 in the Laughlin liquid at an electron filling factor of 1/3 has been studied. It has been found that there are two types of excitations with the same energies, the relaxation times of which to the ground state differ by at least two orders of magnitude. Assumptions are made about the nature of these excitations.

To study the spatial distribution of the intensity of an X-ray source of electric discharge plasma, a new-type coded aperture, which is a structure of intersecting mutually perpendicular transparent and opaque strips with the widths selected using a random number generator, has been used. The radiation passed through the coded aperture has produced a complex pattern of the coded image, which has been recorded on a Fuji TR fluorescent imaging plate without a protective coating. A mathematical procedure based on the iterative method of solving an incorrectly posed problem given by the Fredholm integral equation of the first kind has been applied to reconstruct the spatial distribution of plasma radiation intensity from this pattern. It has been shown that the use of the coded aperture not only has increased significantly the light intensity of the recording system in comparison with a pinhole camera, but also has made it possible to obtain a spatial resolution of the discharge plasma no worse than the resolution of the pinhole camera. The applicability of the developed iterative method for both sources close to point ones and extended emitting objects has been demonstrated.

Resonant interactions of a coherent field with an anharmonic oscillator are classified based on the established analogy with multiphoton interactions of light with atoms. It is shown that interference interactions in which the absorption of a single coherent field quantum induces a multiphoton transition in the anharmonic oscillator are superpositions of resonances of the “cascade” and “lambda-V” types, and a general description of these resonances is given. For the third- and fourth-order nonlinearities, the general expressions are applicable to a resonant process with the absorption of a single photon and the double excitation of the oscillator. Resonant processes of the second harmonic generation and “rectification” of radiation are predicted and described; experimental investigation of these processes will provide information about anharmonicity parameters in the proposed model.

First results on the polarization of (Lambda ) hyperons inclusively produced on 26.5-GeV/c ({{K}^{ - }}) and ({{pi }^{ - }}) beams are presented. The measurements were carried out using the SPASCHARM setup at the U-70 accelerator facility (Protvino, Russia) on nuclear targets in 2021 and 2022. The polarization of an (Lambda ) hyperon on the ({{pi }^{ - }}) beam does not exceed several percent in most of the studied kinematic region. The data obtained on the ({{K}^{ - }})-meson beam exhibit a significant positive polarization at large values of the Feynman variable x_F and transverse momentum p_T measured for the first time on nuclei.

Dusty plasma processes in the physics of comets are considered. The distribution functions of photoelectrons, the altitude dependences of the charges and sizes of dust particles, as well as electric fields are determined using a physicomathematical model for the self-consistent description of densities of photoelectrons and dust particles above the illuminated part of a comet nucleus. It has been shown that dusty plasma processes are significantly manifested when a comet is sufficiently far from the Sun. The dusty plasma near the comet nucleus with the parameters close to the parameters of the nucleus of Halley’s comet at distances to the Sun no less than ~2.5–3.5 AU is formed due to the electrostatic interactions similar to the formation of dusty plasmas near other atmosphereless bodies (e.g., the Moon, satellites of Mars, and asteroids). The dynamics of dust particles at closer distances from the Sun is determined by the gas flow from the comet nucleus.

Since a theory that can justify the condition of matching of the laser and plasma parameters to implement the relativistic self-trapping regime for laser light in a plasma, which is the most efficient for the acceleration of electrons, is still absent, doubts remain in the necessity of the corresponding extensive experimental studies, particularly in view of the lack of justification or completion of previous theories. The presented theoretical analytical approach, which includes the relativistic nonlinearity of the electron mass and electron cavitation in the plasma, allows one to overcome this problem and provides an analytical justification of the conditions of such matching for ultrarelativistic laser beams at the quantitative level, which is in agreement with the multidimensional numerical simulation.

A new mechanism of the generation of a random laser based on a random photonic network with dissipative tunneling of photons between microcavities that are placed at the nodes of such network and contain identical two-level quantum systems has been revealed. It has been shown that an additional source of photon losses in tunneling promotes the separation of individual modes of the random laser and the achievement of the lasing threshold even at a vanishingly small population inversion. In this case, the enhancement of laser modes has an interference nature and is due to the energy redistribution between the nodes of the photonic network that correspond to different signs of the frequency detuning of stationary modes of the random laser from the transition frequency of two-level systems. It has been shown that the traditional lasing mechanism, which demonstrates features of the spectrum of single microcavities, i.e., is almost independent of the topological properties of the network and the tunneling parameter, is present in the region of zero detuning.

The frequency dependence of the complex refractive index of an InAs/GaSb superlattice where plastic relaxation is suppressed by interface compensation of strains and the fundamental absorption edge falls in the far-infrared range is experimentally determined for the first time at temperatures of 77–300 K. The energy structure of the superlattice minibands and its variation with temperature are discussed.

Shubnikov–de Haas oscillations and magneto-intersubband oscillations of the magnetoresistance in structures with single HgTe quantum wells with a width of 10−18 nm have been experimentally investigated. The conduction band spectrum in these arrays is split by the spin–orbit interaction. This leads to beats in the Shubnikov−de Haas oscillations and gives rise to low-frequency magneto-intersubband oscillations. The mutual positions of the antinodes of the Shubnikov−de Haas oscillations and the peaks in the magneto-intersubband oscillations are unusual: at low magnetic fields, they are opposite to theoretical predictions. The measurements in high magnetic fields, at which the relative amplitude of Shubnikov–de Haas oscillations exceeds 0.2–0.3, show a change in the mutual positions of the antinodes of the Shubnikov–de Haas oscillations and the peaks in low-frequency oscillations. Numerical calculations and additional measurements at different temperatures suggest that the observed effects are due to magnetic-field-induced oscillations of the Fermi level.