Physics of Wave Phenomena最新文献

The possibilities of predicting the behavior of the speed of sound in water–alcohol mixtures in dependence of component concentration and under high pressure have been analyzed. A comparative analysis of the thermodynamic properties of water and methanol at high pressures, obtained experimentally and by molecular dynamics simulation for different computer models of water and methanol, was performed, which showed inadequate description of experimental data. It is demonstrated that the existing theoretical methods do not make it possible to study the speed of sound in water–alcohol mixtures at a high pressure, whereas the experimental methods are extremely laborious. Arguments are presented in favor of the fact that the qualitative behavior of the speed of sound in a water–alcohol mixture at high pressures should be similar to the behavior of a mixture of noble gases. The behavior of the speed of sound in an argon–helium mixture in dependence of the component concentration at a high pressure was investigated by the molecular dynamics method. This dependence was found to contain a minimum, which is in good agreement with the experimental data obtained at the same thermodynamic parameters and component concentrations. We present a qualitative explanation of the behavior of argon–helium mixture, based on the Frenkel line concept. Proceeding from this, we suggest that the speed of sound in a water–alcohol mixture under high pressure conditions should also demonstrate a minimum in the dependence on the component concentration.

The spectrum of the high harmonics generated by a Ga⁺ ion exposed to an intense femtosecond laser pulse simultaneously with short-wavelength radiation whose frequency is multiple of the fundamental harmonic and intensity is much lower than the laser intensity has been theoretically investigated. The calculation results show significant enhancement of the radiation of the odd harmonic that is in a multiphoton resonance with the transition from the ion ground state to the autoionizing state 3d⁹4s²4p ¹P₁ and single-photon resonance for the short-wavelength radiation with an increase in its intensity to 10⁹ W/cm². The effect of the enhancement due to the single-photon resonant pump may explain the resonant enhancement of the harmonic observed in experiments with a gallium plasma target.

This work analyzes ion-acoustic shock waves in the presence of an external noise or perturbation by deriving the Korteweg–de Vries–Burgers–Kuramoto (KdVBK) equation. Our plasma model is a five-component magnetized, temperature anisotropic, cometary plasma consisting of two components of electrons (of solar and cometary origin) described by nonextensive distribution functions, a drifting ion component (H₃O⁺) and a pair of oppositely charged oxygen ion components. We have studied the solution of the KdVBK equation in the vicinity of the “inner shock” that occurred at a cometocentric distance of roughly 4000 km for comet 1P/Halley. A drop in the shock amplitude is observed with an increase in the nonextensive parameter of the electrons and as the temperature of the cometary electrons rise. It is found that a shock wave oriented perpendicular to the direction of the magnetic field dissipates more quickly than one that is parallel. As the values of the parallel pressures of H₃O⁺, O⁺ and O⁻ ions increase, the shock amplitude reduces. The dissipation coefficient C is found to rise with increasing kinematic viscosities of ions. Additionally, the shock amplitude exhibits a direct correlation with the ambient magnetic field strength. Also, in general, the shock amplitudes are slightly greater when described by the KdVBK equation rather than the KdVB equation.

Narrow graphene nanoribbons with the width of three carbon atoms and the edge structure of the armchair type (3a-GNRs) are synthesized in inner channels of single-wall carbon nanotubes (SWCNTs) about 1.8 nm in diameter. The method used involves gas-phase filling of nanotubes with 4,4-dibromo-p-terphenyl molecules and subsequent polymerization of individual molecules into graphene nanoribbons inside the tubes. We have established that 3a-GNRs encapsulated in single-wall carbon nanotubes retain their optical and electronic properties. Investigation by the Raman scattering method confirms the structure and high quality of the resulting hybrid systems—3a-GNR@SWCNTs. Like free 3a-GNRs, encapsulated graphene nanoribbons show bright luminescence in the UV/blue and green spectral regions with characteristic features with maxima at the wavelengths of 385 and 555 nm in films and 410 nm in aqueous suspensions of 3a-GNR@SWCNTs. Carbon nanotubes used as containers of graphene nanoribbons allow not only protecting the GNR structure but also individualizing GNRs for subsequent optical measurements. The results are important for further investigations of optical properties of narrow GNR@SWCNTs and practical applications of GNRs in development of photosensitive optoelectronics elements.

For the first time to our knowledge, a single-phase cationic Sr_0.86Ba_0.14MoO₄ solid solution was used as an active medium for multiwavelength generation via stimulated Raman scattering (SRS) on dual (primary and secondary) Raman modes. When pumped by a subpicosecond laser with controllable chirping of radiation pulses (at a wavelength of 1030 nm), single-pass highly transient SRS generation of a larger number of Stokes radiation components (up to six) was obtained as compared to the original SrMoO₄ crystal. This is explained by the increase in the spectral width and relative intensity of the secondary Raman mode in the solid solution. In addition, simultaneous efficient anti-Stokes SRS generation was obtained, especially with a low-frequency shift on the secondary Raman mode due to the small phase mismatch of the Stokes–anti-Stokes parametric Raman interaction. The total efficiency of the Stokes–anti-Stokes SRS conversion reached 33% with an optimal duration of chirped pumping pulses of 2 ps. This makes the obtained simple a source of multiwavelength radiation attractive for use in multiphoton microscopy and photodynamic therapy not only in the second (1000–1350 nm) but also in the first (650–950 nm) therapeutic window of biological tissue transparency.

The electric microfield distribution functions were computed using two approchs: Monte Carlo simulation and analytical calculation. To achieve this, the Kelbg interaction, which accounts for quantum effects at short distances, was employed. Although the focus is on a weak coupling regime where quantum effects are negligible at average interparticle distances, the Kelbg potential was still utilized. In the simulation, all interactions between plasma components were fully accounted for, while the analytical calculation relied on the independent particles model (emitter–perturber). The results were compared with other findings that either include or exclude quantum effects. Various behaviors of the microfield distribution functions were identified. Additionally, the spatial derivatives of the microfield distribution functions were analytically derived, considering all interactions. These functions and their spatial derivatives were then incorporated into the calculation of the spectral line shape Ly-α of the pure plasma Li⁺², which was subsequently used to determine the electrical permittivity of the plasma. The obtained results for the electrical permittivity of this plasma are quite similar to those found in the literature. These results are important for modern applications. It has been shown that quantum action at zero interparticles has an important role in the microfield distribution functions in strongly correlated plasmas, where the degree of quantification is relatively large.

Raman scattering spectra in crystals of TlGa_xIn_1–xTe₂ solid solutions are investigated, frequencies of modes of the solid solutions are determined, and the spectrum behavior character is revealed. Contributions from various atoms of the TlGa_xIn_1–xTe₂ solid solutions to the phonon density of states are determined from first principles, phonon spectra are constructed, and frequencies of solid-solution modes are calculated.

The dependence of the photostimulated multipulsed laser nanoablation of single-crystal diamond on the sizes of the irradiation spot (1.5–5 µm in diameter) and external heating in the range of 300–500 K has been investigated. A possibility of controlling efficiently the performance of this laser nanoprocessing mode and forming atomic-scale nanostructures on the diamond surface is demonstrated.

The paper discusses the prospects of using single-frequency fiber lasers based on two different types of active fibers from the point of view of their applying for interrogating hydroacoustic antennas. Two single-frequency fiber lasers fabricated from two different types of erbium-doped fibers have been demonstrated. One of the lasers was made using conventional erbium doped fiber manufactured by vapour phase deposition technique. Another was based on a new type of fiber made by sintering phosphate glass in a silica glass tube (composite fiber). Both fibers were photosensitive to laser radiation at a wavelength of 248 nm (KrF excimer laser), and laser cavities were inscribed directly in the core of these types of active fibers. Stable single-frequency lasing was obtained for both laser configurations. The maximum value of relative intensity noise measured at the frequency of relaxation oscillations was approximately the same for both laser configuration: –82 and –86 dB/Hz, but the generation bandwidth in the conventional fiber laser was lower: 6.5 kHz instead of 14 kHz in composite fiber laser. Due to the high concentration of erbium ions the slope efficiency of the laser based on composite fiber was 0.98% compared to a conventional erbium doped fiber laser (0.19%).

A high-sensitivity fiber-optic interferometric horizontal accelerometer using passive phase demodulation is proposed and demonstrated. The principle of sensitivity improvement using multiturn optical fiber coil as a horizontal sensing element is described. A fiber-optic 3 × 3 splitter is used as a phase demodulator. The optical responsivity for the frequencies below the resonance was found to be equal 1770 rad/g. Accelerations as small as 0.16 μg at 55 Hz have been detected. The noise level of a fiber-optic accelerometer was compared with a piezoelectric accelerometer. The intrinsic noise level of the fiber-optic accelerometer is lower than that of the piezoelectric accelerometer and provides an opportunity to detect accelerations down to 5 × 10^–8 g. Operating frequency band is 10 to 130 Hz.