Physics of Wave Phenomena最新文献

Micellar aqueous solutions of ionic surfactants have been observed to exhibit proton delocalization (the nuclear quantum effect) and to oscillate between a low density (LDL) and a high-density liquid (HDL) state of water at a fixed temperature. It is shown in this paper that such phenomena can be explained with the help of the interpolating Schrӧdinger equation proposed by Ghose. The nuclear quantum effect can be described by the tunneling of a harmonic oscillator in a symmetric double-well potential, and an ensemble of harmonic oscillators can model the LDL-HDL oscillations. The thermodynamics of such harmonic oscillators has been worked out showing continuous transitions between the quantum and classical limits.

We propose methods for estimation of the number of the sources and their localization in complex mechanical systems. These methods are based on the matching vibrational field obtained using finite element modeling with the measured field from vibration sensors. A modification of the MUSIC (Multiple Signal Classification) algorithm, which is often employed in direction-of-arrival estimation of wavefield sources, is effectively used to localize several simultaneously operating sources of vibration. Numerical simulation and experimental testing in mechanical systems showed the superior efficiency of the proposed method in comparison with the methods previously used to solve similar problems.

The harmonic phase dependence on the laser field intensity is one of the key properties of high-harmonic generation (HHG) in intense laser field. We have studied this dependence both analytically and numerically. Our method, in contrast to other approaches, does not use any phenomenological parameters. We suggest an analytical equation describing the dependence of the harmonic phase on the laser intensity. Analytical results agree with the results of numerical integration of the 3D time-dependent Schrödinger equation (TDSE) for a model one-electron atom in external laser field. We compare the analytical and numerical results obtained for two different fundamental wavelengths and various fundamental intensities. The investigated dependence of the harmonic phase leads to curved harmonic wavefront in the case of generation in the laser beam focus. We suggest an equation for this curvature, whose solution agrees well with the numerical results. Finally, we present an equation for the radius of curvature of the harmonic wavefront generated at some distance from the focus of the generating beam.

The spectra and kinetics of selective and continuum thermodynamically equilibrium emission of electromagnetic radiation from Er₂O₃ microcrystals and a ruby single crystal in the visible and near-IR spectral regions under laser–thermal excitation by electric-discharge CO₂ lasers at a wavelength λ = 10.6 µm in the cw and pulsed modes have been experimentally investigated. The effect of the delay of continuum emission fronts and intensity peaks relative to laser pulses is explained by the difference in the temperatures of the heated layer and electromagnetic radiation. The delay time of the electromagnetic emission maximum is the characteristic time for establishing thermal equilibrium.

We demonstrate a novel approach to inversely design one-dimensional (1D) photonic stubbed systems with targeted topological properties by leveraging the power of deep learning. The process involves developing a data-driven model to accurately predict the geometric parameters of the photonic system based on a label vector that encodes the targeted topological properties. A tandem network comprising an inverse network connected to a pre-trained forward network is trained to efficiently learn the intricate relationship between the system’s topological properties and the corresponding geometry. After training, the model is shown to effectively perform the inverse design task. The study’s outcomes give new perspectives for the design of topological photonic systems.

Irradiation of carbon-containing liquids by ultrashort laser pulses makes it possible to synthesize linear carbon chains (polyynes), which are of great practical interest for optics and electronics. To obtain homogeneous suspensions of polyynes, it is important to study the stability of synthesized structures and search for efficient methods of separating polyynes from laser processing byproducts. In this study polyynes were synthesized using irradiation of graphite suspensions in ethanol by a picosecond laser source (τ = 10 ps, f = 10 kHz, λ = 1064 nm). The processed suspensions contained polyynes of different length (C₈H₂–C₁₆H₂) and some other carbon components. The stability of polyynes was investigated, and a systematic comparison of the results of separating polyynes from other components of irradiated suspensions using filtering, sedimentation, and centrifugation was performed. The optical properties of synthesized polyynes were investigated by optical spectroscopy. The laser processing byproducts were studied using transmission electron microscopy.

Consideration is given to various forms of energy balance relations that describe the influence of the scatterer on radiation of given currents and are connected with the classical description of the Purcell factor and with the optical theorem. It is shown that these relations hold not only integrally but also locally, i.e., for integrands. A transition is described from the ordinary integral form of the scattering problem (of the type of the Lippmann–Schwinger equation) to the system of two equations for the Hermitian and anti-Hermitian parts of the scattering T-operator, so that for the former the diagonal matrix element corresponding to an arbitrary incident wave directly gives the general form of the optical theorem. A particular case is also described, which concerns nonradiating currents in the absence of the scatterer with their radiation loss being only due to the presence of a scatterer.

The spectrum of high-order harmonics generated in interaction of an intense femtosecond laser pulse with a singly charged gallium ion is theoretically investigated. The results of the calculations reveal enhancement of odd harmonics that are in resonance with the frequency of the transition from the ground state to the odd autoionizing state 3d⁹4s²4p ¹P₁ and harmonics that correspond to the multiphoton resonance with the even autoionizing states 3d¹⁰4p5p ¹S₀ and ¹D₂ (dark states) and are one laser frequency away from them. The effect of resonant enhancement of harmonics was earlier observed in experiments on gallium targets with a plasma plume.

The possibility of observing the mode coupling effect, caused by a local inhomogeneity, is studied for a long-range stationary acoustic track between a single sound source and a single receiver in a shallow-water waveguide. This effect manifests itself in the form of oscillations of normal mode amplitudes in the frequency domain and can be used to localize inhomogeneities. An analytical formula linking the oscillation period of the first-mode amplitude with the distance to the inhomogeneity is proposed. Numerical experiments with a model inhomogeneity in the form of a local bottom rise show that the frequency dependence of the mode amplitude can be selected not only at a vertical line array but also at a single receiver, with the use of warping transform. In this case, the receiver depth should correspond to zero of the second-mode vertical profile. The dependence of the mode amplitude oscillations on the local inhomogeneity size is discussed.

The concept of a phase invariant (PI), introduced in our previous studies, is used to describe the sound-field phase distribution in an underwater waveguide in the distance–frequency plane. This concept is similar to the classical waveguide Chuprov invariant (ChI), which specifies the slopes of constant-field intensity lines in the same plane. The PIs of vector–scalar fields excited by multipole sources are investigated for the first time in this paper. It is shown that, as well as in the case of a monopole source, PI is a stable characteristic of a sound field. It is demonstrated by numerical simulation that the PI value in shallow water barely depends on the source directional pattern, the path length, the frequency of emitted signal, and the waveguide characteristics. Significant deviations of PI from its basic value (–1) are observed only in the vicinity of interference minima (in the phase-dislocation zones).