Physics of Wave Phenomena最新文献

A two-wavelength diode laser spectrometer has been developed and simultaneous changes in the concentrations of water and oxygen molecules in their mixtures with helium were observed. The concentrations behavior has been investigated at different stages: at the gas injection cycle into an evacuated tube, during burning of a DC glow discharge and at the phase after its shutdown. The measurements were carried out by the absorption of light on weak lines of vibrational-rotational intermode transitions of H₂O and spin-forbidden electron transitions of O₂ at reduced pressures of several millibars with concentration sensitivities of 10¹⁴ and 10¹⁵ cm^–3, respectively. Under such conditions, in addition to homogeneous interactions, heterogeneous interactions of particles with each other and with active surface centers are significant in the formation of the chemical composition of gases. It has been established that for different molecules that are stable under normal conditions, the concentrations at the discharge stage and its afterglow may not correspond to each other. This depends on the type of molecule, the composition of the plasma-forming mixture containing these molecules, the conditions of preparation and the operating mode of the reactor; imbalances of elements in the bulk phase are noted. The experimental results were interpreted using a plasma-chemical kinetic model of a direct current discharge in an O₂–He–H₂O gas mixture taking into account the interactions of electrons, ions and neutral particles in the ground and excited states. In addition to solving the kinetic equations for chemical reactions and the Boltzmann equation for electron energy distribution function, the model provides the profiles of gas temperatures and axial electric field strengths, and takes into account the effect of heating of the neutral gas in the non-equilibrium discharge plasma on the measurement results. To explain the imbalance of elements, in addition to the known heterogeneous processes of particle recombination, it is postulated that previously undiscussed chemical reactions of the decay products of the initial molecules in the plasma occur with particles adsorbed on the walls at the stage of filling the reactor with the plasma-forming gas. The model satisfactorily describes the results of measurements of particle concentrations in the discharge and afterglow stages, and the main macroscopic parameters of the discharge.

Amplitude-phase characteristics of sound pressure (SP) in the deep ocean is analytically and numerically investigated under summer conditions. To this end, analytical relations are obtained, which allow calculating and comparing space–frequency structure characteristics of water, leaky, and trapped modes, as well as of the SP field formed by the mode sum. The calculations are performed using the modified Wentzel–Kramers–Brillouin approximation. It is shown that modes of different types dominate at different distances, and this enables describing structure variability of both the amplitude and the phase distribution of the SP field in different zones with a different mode composition. It is found that in the field based on the sum of all modes the mode properties more distinctly manifested at various distances are of those modes which dominate at these distances. As a consequence, space–frequency structures of SP amplitudes are substantially different in different zones. But, due to stability of phase gradients in zones of interference maxima, phase surfaces coincide in shape for all types of modes, all frequencies, and almost all distances. Some difference is only observed for leaky modes in the near-field zone. Numerical values of effective phase velocities of the summed field depend, as expected, on phase velocities of modes of various types and on their “extinction” rate, and they are appreciably different in different zones. This should be taken into account during direction finding and estimation of noise source coordinates.

An experimental setup based on a powerful ultrawideband microwave source is devised to investigate absorption spectra of gaseous substances. A technique is developed for measuring the absorption coefficient of a substance. It is based on detection of a change in the spectrum of microwave radiation on its passing through the substance under study and is therefore low sensitive to features of the incident radiation spectrum. The accuracy is further increased by multiple repetition of measurements. Rotational spectra of organofluorine compound C₄F₉I vapor are investigated. In the spectral range under consideration, a number of microwave radiation absorption peaks are observed in this compound.

Phase-change materials are very interesting and promising objects for various optical applications due to simple and high-speed switching between the amorphous and crystalline states. In this study, we consider the specific features of laser crystallization and ablation of thin amorphous Ge₂Sb₂Te₅ films exposed to the HG₀₁ (Hermite–Gaussian TEM₀₁) mode of cw visible light. This exposure led to two-zone crystallization or ablation, depending on the laser intensity. Microscale two-zone ablation made it possible to observe Young’s fringes for the radiation transmitted through a sample, as in the case of two-point-source interference. This approach is promising for express analysis of the laser beam profile.

Effective noise amplification is detected for the first time at the interaction of a relativistic electron beam with slow plasma waves in a coaxial plasma–metal waveguide. Unlike configurations of existing plasma masers, this configuration of the plasma–beam interaction region can be used for long operation in the pulsed-periodic mode with the hollow electron beam deposition on an easily cooled collector. In addition, the internal metal conductor at the ground potential increases the limiting vacuum current of the electron beam and the current at which the maximum transfer efficiency of the electron beam energy to the plasma wave is achieved. The electron beam with the energy of 250 keV, current of up to 1.5 kA, and duration of 2.5 ns has interacted with the plasma waves with the measured concentration of up to 3 × 10¹³ cm^–3. A radiation spectrum from 2 to 6 GHz with the power of up to 70 MW is recorded.

In this study, we investigate optical bistability in one-dimensional photonic crystals using Fibonacci layer sequences. We introduce a novel approach by incorporating vanadium dioxide (VO₂) into these sequences, deposited on a glass substrate with a negative refractive index material. Our works reveal significant high transmission peaks in the microwave spectrum, characterized by both optical bistability and multistability. We explore the theoretical implications of various parameters, including the VO₂ filling fraction, layer thickness, and incidence angle, on light transmission within this novel structure. Additionally, we demonstrate how temperature and phase variations in the VO₂ layer can modulate transmission peak characteristics and induce optical bistability. These adaptable structures show considerable promise for developing optical devices with controlled transmission peaks, with potential applications ranging from optical switches to tunable microwave filters. The observation of optical bistability at critical transmission wavelengths in the microwave range represents a highly desirable outcome with broad implications.

The structural transformations occurring in a chlorine monolayer on a previously oxidized Ag(111) surface, containing Ag₆O₆ oxide rings centered at vacancies in the upper silver layer, were investigated using scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. It is found that, at a temperature of 80 K in the initial stage, chlorine atoms form chain structures in the gaps between oxide rings. As the coverage increases, chlorine forms domains having a uniaxially compressed structure, with boundaries determined by the local oxide. Continued Cl₂ adsorption leads to condensation of molecular chlorine. Annealing of the resulting system to 300 K causes significant structural transformations on the surface, resulting in the formation of islands of (20–30) Å in size with the reconstruction Ag(111)-(3 × 3)-Cl, as well as chains of objects with a height of ≈1 Å. Based on the DFT calculations these objects were found to be O–Cl quasi-molecules, formed by surface oxygen atoms and adsorbed chlorine atoms.

Sixteen approximations of the density functional theory for calculating the structure and Raman spectra of the most stable α-phase of poly(L-lactide) (PLLA) with an orthorhombic crystalline lattice have been analyzed. It is shown that the GGA functionals OLYP and PBE provide good correspondence with experimental X-ray diffraction and Raman spectroscopy data. It is found that, when using extended basis sets of three- and four-exponential types, the choice of the functional affects the calculation results much more radically than the choice of the basis set.

Abstract—Influence of nonlinear hydrodynamic effects on formation of pressure pulses investigated in condensed media under pulsed actions leading to fast local variation in their density. In contrast to the ordinary thermoacoustic mechanism where density variation is caused by absorption of the incident radiation energy, models with the given space–time perturbation of density in an incompressible fluid are considered. It is shown how hydrodynamic nonlinearities give rise to transformation of a pressure pulse generated at different perturbation amplitudes and durations.

The laws of amplification of electromagnetic fields in thin ferromagnetic films due to the local surface plasmon resonance have been investigated for structures of spintronic THz emitters. The optimal parameters of Pt/Co and Pt/Co/W plasmonic structures, providing maximum optical absorption in the films at a wavelength of 800 nm, have been determined using numerical simulation. The results show that the use of plasmonic structures makes it possible to increase the optical absorption in Pt/Co and Pt/Co/W structures to 25 and 18%, respectively. The structures are found to have high polarization sensitivity, which manifests itself in high absorption anisotropy, equal to 0.9.