Physics of Wave Phenomena最新文献

An improved optical ultramicroscope is described to be used for visualizing single nanoparticles (NPs) sized over 5–10 nm in aqueous solutions and determining their hydrodynamic radii. The ultramicroscope is based on detection of Brownian motion trajectories of NPs using the elastic light scattering signals of two—laser and nonlaser—sources and their subsequent analysis for determining individual hydrodynamic radii of the detected NPs. The actual capabilities of the developed microscope in studying NPs of a different nature, including biological ones, are demonstrated. The analysis results for silver and silicon dioxide (SiO₂) NPs obtained using the developed microscope are compared to those obtained using a transmission electron microscope and a dynamic light scattering microscope (DLS). The developed microscope is shown to hold promise in medical diagnosis applications. Advantages of using a nonlaser source of bright incoherent radiation for analysis of submicron particles larger than 100 nm are demonstrated.

The effect of γ-irradiation from a ⁶⁰Co source in the dose range 5 × 10⁵–10⁷ rad on the optical and luminescent properties of the UPS-923A plastic scintillator based on a polystyrene matrix doped with para-terphenyl (pTP) and a 1,4-bis(5-phenyl-2-oxazolyl)benzene (POPOP) spectral shift additive was investigated. UV–Vis absorption spectroscopy, excitation and photoluminescence spectra, as well as IR spectroscopy methods showed that radiation degradation is selective and primarily affects POPOP molecules containing oxazole rings, while pTP demonstrates higher radiation resistance in the initial stages of irradiation. It has been established that at low doses of irradiation, a relative stabilization of pTP luminescence is observed, while the intensity of POPOP radiation decreases already at doses of about 10⁶ rad. Analysis of the difference spectra and the evolution of the IR bands indicates the destruction of C–N and C–O bonds in the POPOP structure, which leads to a disruption of the energy transfer mechanism between the additives and a decrease in the light output of the scintillator. The results obtained allow us to propose a physicochemical mechanism for the radiation degradation of UPS-923A plastic scintillator and can be used in the development of radiation-resistant organic scintillators for high-energy radiation detectors.

The formation of stable birefringent micromodifications (voxels) in silica glass by single ultrashort laser pulses with a flat-top intensity profile has been studied experimentally and theoretically as a function of the focusing numerical aperture. It is experimentally shown that birefringence is formed in a voxel if the focusing numerical aperture is higher than 0.5, while lower-aperture focusing gives rise to voxels without birefringence. The slow axis of birefringence is predominantly oriented along the polarization of the incident light, and the azimuthal dispersion of the axis direction decreases with increasing numerical aperture.

The electromagnetic energy transfer in single- and double-wire transmission lines has been considered. This transfer is shown to be implemented by intrinsic surface electromagnetic waves in wire lines. The wave dispersion relations are determined, decrements of their spatial damping and spatial distributions of electromagnetic energy flows are calculated, and the energy balance at surface wave propagation in transmission lines is investigated. The existence of a limiting transition from a transmission line with a source and load to a closed dc current chain is demonstrated. The first part of the study is devoted to the investigation of surface waves in planar-layered systems in the form a conductive sheet, a double conductive sheet, and a flat conductive layer.

The acceleration of electrons in a laser plasma excited by subterawatt femtosecond pulses in gas-cluster targets of different types has been experimentally studied. The laser–plasma interaction was investigated under different target pumping conditions. A possibility of generating a narrowly directed beam of electron bunches with average electron energy up to 90 keV under excitation of a gas-cluster jet, containing nanoscale sulfur hexafluoride molecular clusters, by laser pulses of subrelativistic intensity (up to 10¹⁶–10¹⁷ W/cm²) was experimentally demonstrated for the first time. The main characteristics of the pulsed electron beam generated under optimal jet excitation conditions have been measured, and the generation of THz radiation, accompanying the electron acceleration, has been investigated as well.

The electronic band structure, origin of energy states, spectral dependences of optical functions at different polarizations of incident light and partial densities of states projected onto atoms have been studied for TlInS₂ crystals of hexagonal modification using ab initio calculations. The linear and nonlinear optical properties of this compound were experimentally investigated in the range of photon energies from 0.7 to 6.5 eV by spectral ellipsometry. The experimentally found spectral dependences of the imaginary and real parts of the dielectric function; optical conductivity; refractive indices; and extinction and absorption coefficients are in good agreement with the calculation results. The nonlinear refractive index, as well as the first- and third-order nonlinear susceptibilities, were calculated; the found values indicate good prospects of integrating the compound under study into various nonlinear optical systems.

Piezothermoelasticity and wave interaction studies play a vital role in the development of functional devices such as transducers and sensors, which are widely used in energy harvesting and structural health monitoring. Motivated by these applications, this paper investigates the reflection of plane waves at the boundary of a piezothermoelastic half-space for a traction free surface. A particular focus on the influence of initial stress is examined. Four reflected wave modes such as quasi-longitudinal (qP), quasi-shear vertical (qSV), electrical-acoustic (EA), and thermal (T) are considered. By apply the boundary conditions, a coupled system of linear algebraic equations is obtained. This is solved to express the corresponding amplitude ratios explicitly as functions of the angle of incidence. These expressions are solved by using appropriate mathematical tools, and numerical simulations are conducted for a piezothermoelastic material, such as barium titanate (BaTiO₃). The study compares results under two thermoelastic theories: Lord and Shulman (LS) and Green and Lindsay (GL). More energy shifts into the qP wave, while the qSV wave becomes weaker, which helps when a clear qP signal is needed in practical devices. The effects of initial stress on wave behavior are demonstrate graphically and it provides a valuable intuition for smart material design and wave-based sensing technologies.

A short-cavity laser based on a heavily doped ytterbium (6.3 wt % Yb³⁺) composite optical fiber with a phosphate core and silica glass cladding, operating in continuous and pulsed modes, is presented. Two- and three-mode lasing regimes were implemented under continuous pumping; beats of orthogonally polarized modes with frequencies of 11, 13, 14, 15, and 24 GHz were observed in these regimes. Gain switching was implemented under pulsed pumping, in which the laser operated on one longitudinal mode; the pulse duration varied from 107 to 213 ns.

The intrinsic emission spectra of a 50-µm-thick water layer in the range of 0.2–7 THz at temperatures from 30 to 90°C have been recorded. An excess of emission intensity above Planck’s limit is found in the range of 0.3–0.5 THz at temperatures of 60°C and higher. The value of this excess increases with increasing the heated liquid temperature. Attention is paid to the correlation between the occurrence of the revealed selective nonequilibrium emission with the formation of air bubbles in the liquid.

A new simple method is proposed for producing bulk air nanobubbles (NBs) in water by filtration through a dry Anopore membrane (Anodic Aluminum Oxide, AAO) with a pore diameter of 20 nm. Unlike the case in traditional membrane approaches, where a gas is passed through a membrane, in this method water is forced through a dry membrane. It is shown that filtering through hydrophilic polyethersulfone membranes with the same nominal pore size does not lead to formation of bubbles. Properties of the resulting nanodispersions are investigated using the dynamic light scattering (DLS), ultramicroscopy, and nanoparticle tracking analysis (NTA) methods. It is found that NBs with a low initial concentration and a hydrodynamic radius of ~50 nm are formed immediately after filtering. Within 10–15 min, the NB concertation increases to a stable level of about 10⁸ particles/mL, and their average size becomes larger. Thirty minutes after generation, the size distribution measured by the NTA method has a maximum at a radius of ~78 nm. Dispersion demonstrates a considerable time stability: after 24 hours the NB concentration remains at a level of ~10⁷ particles/mL. The proposed method is a simple reproducible laboratory technique of producing stable nanobubble dispersions.