Bulletin of the Russian Academy of Sciences: Physics最新文献

The generation of broadband terahertz radiation by optical pulses in a nonlinear uniaxial crystal is studied through numerical simulation. This process is accompanied by the creation of a stable optical-terahertz soliton and an additional broadband terahertz signal.

The dynamics of propagation of electromagnetic pulses consisting of a single field oscillation in a composite system of carbon nanotubes integrated into a polymer matrix was studied. Nanotubes with an impurity energetically isolated from the zone structure of nanotubes were considered. An influence of the composite parameters on the processes of propagation of ultrashort pulses was revealed, which opens up new possibilities for controlling their characteristics in such hybrid systems.

The dynamics of a laser beam in a nonlinear medium with carbon nanotubes under the influence of external electromagnetic fields was theoretically studied. Application of the method of slowly varying amplitudes to the nonlinear wave equation allowed one to derive a modified parabolic equation for the spatiotemporal evolution of a Gaussian beam. The influence of electric and magnetic fields on the main radiation parameters, including the maximum intensity, was estimated. The obtained results demonstrated a significant dependence of the radiation characteristics on both the parameters of the laser beam itself (frequency, initial amplitude) and the external constant electric field.

Ce_0.50Y_0.44–xTb_0.06Eu_xF₃ nanoparticles (x = 0, 0.015, 0.03, 0.06) of single-phase hexagonal structure (CeF₃ matrix) are synthesized via co-precipitation. The average particle size is found to be 14.5 nm. Characteristic emission bands are observed upon excitation at 266 nm: Ce³⁺ (5d → 4f transition), Tb³⁺ (⁵D₄ → ⁷F_J, 480–620 nm), and Eu³⁺ (⁵D₀ → ⁷F_J, 570–700 nm). The temperature dependence of integral intensities and their ratios (Ce³⁺/Tb³⁺, Ce³⁺/Eu³⁺, Tb³⁺/Eu³⁺) are studied in the 80–320 K range of temperatures. The highest sensitivity toward temperature is obtained for ratio Ce³⁺/Eu³⁺ at Eu³⁺ concentration x = 0.03. Kinetic studies of Tb³⁺ luminescence confirm temperature-induced quenching due to enhanced phonon-assisted transfer of energy to Eu³⁺.

A new approach was considered that combines generation methods in optical fibers with a strongly modified dispersion profile and nonlinear crystals with periodic poling. The results of numerical analysis showed the rich potential of such systems for generating quantum states, in particular, for generating ultrabroadband states for two-photon microscopy applications.

Under the conditions of the Markov approximation, a master kinetic equation is derived that describes the transfer of the state of a single-photon packet to the state of a solitary object, depending on the nature of the latter. A single-photon excitation is a broadband packet with a Gaussian frequency distribution (an information signal) that interacts nonresonantly with a selected high-Q cavity mode (an intermediary). The latter also interacts nonresonantly with an absorber whose natural frequency is resonant to the central frequency of the packet.

In metal-enhanced fluorescence of nanoparticles with rare earth ions, the number of photons and the rate of spontaneous transition are increased due to localized plasmon resonance. The model describes a nonmonotonic dependence of the quantum yield on the concentration of gold nanoparticles. The maximum is achieved due to the balance between the Purcell effect and optical absorption. These results are useful for the development of biological sensors with increased sensitivity.

To determine the optimal parameters of optical random number generation and mathematical postprocessing based on the lexicographic numbering of the noise of the optical random number generator, an integral indicator is proposed that combines the normalized values of three metrics: the arithmetic mean and the median percentage of successful NIST tests, as well as the proportion of results exceeding a given threshold.

In the electron paramagnetic resonance spectra of crystals of narrow-gap semiconductor Pb_1–xGd_xS ((3.2 times {{10}^{{ - 4}}} leqslant x leqslant 9.5 times {{10}^{{ - 3}}})), unusual changes in the shape of the lines of Gd³⁺((4{{f}^{7}},;,S = 7{text{/}}2)) centers were detected, which are caused by a change in the concentration of impurity gadolinium. The spectra of the studied crystals with increased gadolinium concentrations also show weaker additional lines of two types of new gadolinium centers with cubic symmetry of magnetic properties and with effective electron spins of (S = 7{text{/}}2) and (S = 5{text{/}}2.) Two possible explanations for the observed properties of the discovered paramagnetic centers were proposed.

The effect intermolecular interactions have on the conformational equilibria of several ethane-like compounds in a mixture of polyvinyl chloride and polyvinyl butyral is analyzed via Fourier-transform IR spectroscopy. The differences between enthalpies in the conformations of ethane-like compounds in a polymer mixture are determined, and the contributions from intermolecular interactions are estimated. The contributions from intermolecular interactions of ethane-like compounds, the polymer mixture, and the components of the mixture are compared.