Bulletin of the Lebedev Physics Institute最新文献

We report the results of experimental studies on the effect of ultraviolet (UV) radiation in a wide spectral range of 270–405 nm on bovine coronavirus. The sensitivity of bovine coronavirus to UV radiation is determined, a comparative analysis of the data is performed, and action spectra are constructed. It is shown that bovine coronavirus inactivation is possible in the UV-A range, which will make it possible to select safe radiation sources for use in public places in the presence of people.

We report a detailed study of the structure and absolute intensities of lines in the X-ray spectra of laser-produced tungsten plasmas. Plasmas are generated by focusing a laser pulse (0.53 μm, 5 J, 2 ns) onto massive solid targets. The spectra are measured by two focusing crystal spectrometers in the wavelength range of λ = 4–8 Å with a spectral resolution of λ/δλ = 600–1500. Plasmas are diagnosed using spectra of [He]-like ions of light elements. Absolute spectral brightness of the source is measured, and the temperature of tungsten plasma electrons in the range of T_e = 500–750 eV is estimated using the comparison method.

Spectrа of the Xe₂Cl(4²Г → 1²Г) laser transition and transitions from the Xe₂Cl(4²Г) state to the highlying states were modelled using the previously obtained results of quantum chemical (ab initio) calculations of the electronic structure and the dipole moment functions of optical transitions of the Xe₂Cl molecule. It has been established that the long wavelength wing of the laser transition band overlaps with the short wavelength wing of the Xe₂Cl(6²Г ← 4²Г) absorption band; the long wavelength threshold in the known from the literature generation spectra of the Xe₂Cl(4²Г → 1²Г) laser is located in the specified overlap region. The possible effect of absorption at the Rg₂X(6²Г ← 4²Г) transition on the generation spectra of other Rg₂X(4²Г → 1²Г) lasers, as well as a number of other issues related to intracavity absorption in the active medium of lasers of this type are discussed, in particular, absorption at transitions from metastable states of Rg atoms.

We report the effect of the built-in electric field emerging in elastically strained multiple InGaAs/GaAs quantum wells on the THz generation efficiency upon irradiation of the surface of these heterostructures, as well as photoconductive antennas based on them, with femtosecond optical laser pulses. The built-in field arises as a result of the piezoelectric effect in heterostructures with multiple {InGaAs/GaAs} × 10 quantum wells grown on GaAs substrates with (110) and (111)A crystallographic orientations. Terahertz radiation produced under the same excitation conditions from films with the same composition, but grown on substrates with different orientations, is compared. The most intense THz radiation is obtained from the surface of the {In_0.2Ga_0.8As/GaAs} × 10 heterostructure on a GaAs (110) substrate. Among photoconductive antennas, the highest efficiency of THz generation is demonstrated by antennas made on (110) and (100)-oriented {In_0.2Ga_0.8As/GaAs} × 10 heterostructures. In this case, the influence of the substrate orientation, which is clearly manifested upon generation of THz radiation directly by the surface of the films, is much weaker for photoconductive antennas on the same films.

We examine the features of the formation of the transfer functions of an acousto-optic spatial filter made of a uniaxial gyrotropic crystal operating in tangential diffraction geometry. It is shown that a decrease in the sound frequency is accompanied by distortions of the transfer functions on the side facing the optical axis of the crystal. The distortions are caused by the influence of the second diffraction order on the distributions of axisymmetric transfer functions. The cutoff frequency of sound below which the transfer functions become practically unsuitable for two-dimensional processing of optical images is determined. It is shown theoretically and experimentally that the cutoff frequency of sound for processing a two-dimensional image with a wavelength of 0.63 μm using a spatial frequency filter made of ТеО₂ is ∼40 MHz.

We report the results of a study of laser-induced transparency under the conditions of the optical Stark effect in CdSe nanoplatelets. The induced absorption spectra are measured by the pump–probe technique. Laser-induced transparency is observed due to the transfer of the population of the electron states of the valence band to the conduction band as a result of two-photon optical transitions under the action of pump radiation. The transparency of the medium is maintained for the lifetime of the first excited exciton level, which corresponds to 180 ps. The presence of a hypsochromic shift of the exciton absorption band by 3.1 meV for a pump power density of 39 GW/cm² with the coincidence of pump and probe pulses due to the optical Stark effect is demonstrated. The results of fundamental studies presented in this paper can find application in the development of new photonic devices for controlling light with light.

We performed an experiment on the acceleration of electrons in the laser peeler regime during the interaction of a focused subpetawatt laser pulses with solid-state targets. Electrons with energies up to 70 MeV were produced, and their directional pattern was determined. The use of serrated targets led to an increase in the maximum energies and the number of accelerated electrons. A numerical study conducted using particle-in-cell simulation showed good agreement with the experimental results.

Recent results of studies of Ξ_b baryons properties and decays are discussed, based on the data collected by the CMS experiment at the LHC in proton collisions with 13 TeV energy in 2016–2018, corresponding to an integrated luminosity of (140{kern 1pt} {kern 1pt} {text{f}}{{{text{b}}}^{{ - 1}}}{kern 1pt} ). The CMS experiment reports the first observation of the new decay (Xi _{b}^{ - }) → ψ(2S)Ξ^–, as well as the measurement of its branching fraction with respect to the known decay (Xi _{b}^{ - }) → J/ψΞ^– . Precise measurements of the (Xi _{b}^{{*0}}) baryon mass and natural width are also presented, with the ratio of the (Xi _{b}^{{*0}}) and (Xi _{b}^{ - }) production cross sections.

The investigation results of magnetization, dynamic magnetic susceptibility and microstructure of samples of second generation high-temperature superconducting wires irradiated by Bi ions at room temperature with energy of 670 MeV and fluences of 10¹¹ and 10¹² cm^–2 are presented. The dependences of the superconducting transition temperature and critical current density on the fluence have been determined. For the sample irradiated to fluence 10¹¹ cm^–2, an increase in the critical current density is observed compared to the control nonirradiated sample. The microstructure analysis of irradiated samples demonstrates the presence of amorphous tracks, which can act as effective pinning centers.

The erosion pattern of discharge device elements is studied in a high-voltage pulsed arc discharge initiated by an auxiliary spark discharge on the dielectric surface in a short vacuum gap. A dependence of the operating erosion mechanisms on the time profile of the flowing current is found.