Bulletin of the Lebedev Physics Institute最新文献

The results of particle-in-cell (PIC) simulation of the effect of intense laser pulses (peak intensities of 10¹⁹ to 10²¹ W/cm²) on near-critical density (NCD) plasma have been analyzed. As they propagate through NCD plasma, these laser pulses create an ion channel with lower electron density and strong quasi-stationary fields. Radial inhomogeneity of the electron density creates a radial electrostatic field due to the ponderomotive expulsion of background plasma electrons from the channel. At the same time, the current of accelerated electrons generates an azimuthal magnetic field. In direct laser acceleration (DLA), relativistic electrons trapped in the channel by focusing quasi-stationary fields experience transverse betatron oscillations and gain energy efficiently from the laser pulse when the frequency of the betatron oscillations becomes resonant with the Doppler shifted laser frequency. The potential for producing electron bunches with energies of tens of megaelectronvolts and charges of hundreds of nanocoulombs using DLA in NCD-plasma has been demonstrated. It is shown that the energy spectra of accelerated electrons can be approximated by Maxwell distributions. A scaling is proposed for the dependence of the effective temperature of “superponderomotive” electrons on the laser pulse and plasma parameters.

In this study, we conduct a theoretical analysis of the optical absorption coefficients (OACs) and refractive index changes (RICs) arising from intraband and interband transitions in monolayer germanene under the influence of a magnetic field. The findings reveal that both OACs and RICs blueshift as the magnetic field strength increases. Notably, the peaks associated with spin-up states consistently appear to the right of those corresponding to spin-down states. This distinction in peak positions is attributed to the strong spin–orbit coupling (SOC) characteristic of monolayer germanene. For intraband transitions, the OACs and RICs exhibit a single peak in the terahertz (THz) region. Moreover, interband transitions give rise to multiple peaks, spanning from the high THz range to the low far-infrared range, underscoring the promising potential of monolayer germanene for optoelectronic applications.

We report an investigation of optical and scintillation characteristics of a prototype module of an electromagnetic calorimeter based on a Lu₂SiO_5‒z:Y³⁺:Ce³⁺:Ca²⁺ crystal with the size of 20 × 20 × 90 mm³ and grown by the Czochralski method. The scintillation decay time of the crystal module excited by gamma quanta by a ¹³⁷Cs source is obtained. The energy resolution of the crystal module is estimated by simulating it with the GEANT4 program.

Based on two different nonempirical (calculated ab initio) interatomic potentials, we study the sensitivity of the line shape of the anomalous light-induced drift (LID) to the difference in interaction potentials using Cs atoms as an example and taking into account the real level structure in the atmosphere of inert buffer gases He, Ne, and Xe. It is found that even a slight difference in the interatomic potentials strongly manifests itself in the frequency dependence of the drift velocity in the region of the anomalous LID. The obtained results make it possible to perform high-precision testing of interatomic potentials based on experiments on the anomalous LID of Cs atoms.

The use of millisecond laser sources has become an essential part of clinical practice in assisted reproductive technologies. The biopsy of embryos at the blastocyst stage is one of the challenges addressed in reproductive medicine. We have examined the feasibility of applying femtosecond laser pulses (with a duration of 280 fs and a radiation wavelength of 514 nm) and their effectiveness in solving this problem. The biopsy procedure was performed using micropipettes as part of a standard clinical protocol. It is demonstrated that pulses with an intensity of 4 to 6 TW/cm² can be used to separate bioptate cells. The outcomes of exposure in different regimes (from a single pulse to a sequence of pulses) are presented.

We report a study of a soliton-like regime of second harmonic generation in a crystal containing impurity atoms with a quantum transition, which is quasi-resonant with respect to a laser pulse at the fundamental frequency. Mismatches of phase and group velocities are taken into account. It is shown that quasi-resonant impurities, on the one hand, lead to a decrease in the generation efficiency, and, on the other hand, they are capable of creating conditions for the implementation of a two-frequency soliton regime, which is impossible in their absence.

We report a comparative study of the impact of repetitively pulsed neodymium laser radiation of the first (λ₁ = 1064 nm, τ₁ = 12 ns) and second (λ₂ = 532 nm, τ₂ = 10 ns) harmonics on tableted microparticles of brown (2B), gas (G), and fat (Zh) coals. The concentration of synthesis gas molecules formed when microparticles of hard coals are exposed to laser pulses of the same energy density is higher in the case of the second-harmonic radiation. The concentration of synthesis gas molecules formed when microparticles of coals are exposed to first- and second-harmonic pulses of the same intensity is the same. A model is proposed to explain the nonlinear dependence of the synthesis gas yield on the intensity of laser pulses, based on the nonlinear generation of primary centers of thermochemical reactions formed during optical breakdown of coal samples and generation of laser-induced plasma. The spectral intensity of the laser-induced plasma glow when tableted samples of coal microparticles are irradiated by the second-harmonic laser pulses is higher than that during irradiation by the first-harmonic pulses, with radiation energy densities being the same.

Long-lived electron-beam-induced absorption in a number of UV-optical materials for windows and multilayer coatings of inertial fusion energy reactor and promising KrF laser driver was studied using a pulsed linear electron accelerator with electron energy of 10 MeV. In testing high-purity samples of quartz glasses Corning 7980, KU-1, and KS-4V, as well as crystals of calcium fluoride, magnesium fluoride, and leucosapphire the radiation dose of 18.2 MGy, was comparable to the dose absorbed by windows of KrF electron-beam-pumped laser driver operating for 1 year with a pulse repetition rate of 5 Hz. Quartz glass KS-4V with an admixture of OH showed the lowest absorption with a coefficient of 0.4 cm^–1 at a wavelength of 248 nm among all other glasses. Rather high absorption with a coefficient of 4 cm^–1 in calcium fluoride is effectively bleached by the own KrF laser radiation.

We study the propagation of soft X-rays in conical hollow through nano- and micropores of polymer track membranes. The distribution of the field amplitude and the transmission coefficient of the conical structures are determined. The problem is of interest for two reasons. First, the conical shape of pores in track membranes is the norm rather than an exception to the rule. It is determined by the final ratio of the etching rates of the intact polymer and the membrane material in the track region. Secondly, the concentration of soft X-rays at the output from the conical pores of the sample has been scarcely studied. Calculations are performed for porous membranes made of polyethylene terephthalate at wavelengths of 13.3 and 30.4 nm at normal incidence of radiation on the pore end and at various angles of the pore cone. Examples of calculations for oblique incidence of radiation on the sample are presented, and the effect of the damaged pore wall layer on the calculation results is discussed.

We present a spectrum of primary galactic particles with energies of 10 TeV < E₀ < 500 TeV, obtained from the data of reprocessing of events related to nucleon‒nucleus interactions measured in four X-ray emulsion chambers (RECs) exposed in the stratosphere at ∼10 g/cm² for 6‒7 days in the Russian‒Japanese RUNJOB balloon experiment. The spectrum agrees within statistical errors with the proton spectrum published on the results of the final processing of the RUNJOB experiment [1]. The presented spectrum of galactic particles includes events with found and missing single-charged primary particles in nucleon‒nucleus interactions, and is compared with the spectrum constructed only from events with detected primary protons and the final spectrum of the cosmic ray proton component of the RUNJOB experiment.