Physics of Wave Phenomena最新文献

The electronic properties of ZnIn₂Se₄ crystals have been studied experimentally by spectral ellipsometry and theoretically (from the first principles) using the density functional theory (DFT). Ellipsometric studies in the energy range of 0.7–6.5 eV made it possible to determine the imaginary and real parts of the dielectric function and optical conductivity, as well as the dispersion of the refractive indices, extinction coefficients, and absorption coefficients, and to estimate the values of the Urbach energy, plasma frequency, and nonlinear optical characteristics of ZnIn₂Se₄ crystals. The electronic band structure, origin of energy states, optical functions for incident light polarized along the crystal optic axis and perpendicular to it, and partial densities of states projected onto atoms are determined by ab initio calculations. The theoretical results are compared with the experimental data obtained by spectral ellipsometry.

The paper reports a possibility of using high-power femtosecond laser pulses for imaging and subsequent study (by means of optical microscopy) of small-scale structural inhomogeneities in synthetic diamond single crystals. The irradiation of diamond by laser pulses in the intense self-focusing mode creates conditions for multiple optical microscopic breakdowns, whose distribution in the diamond bulk reflects spatial oscillations of local breakdown threshold. The breakdown-produced sp² inclusions form ordered stripe microstructures with a characteristic period of several microns. It is shown that spatial oscillations of breakdown threshold correlate with changes in the local concentration of impurity–vacancy defects NV and SiV.

The transfer matrix method (TMM) was used to investigate the tunability of the transmittance with an external magnetic field and temperature within the photonic bandgap in the terahertz range. Mg₂Si and CoSb₃ defect layers (D) were used for this in the symmetric (Si/SiO₂)^N D (SiO₂/Si)^N and asymmetric (Si/SiO₂)^N D (Si/SiO₂)^N one-dimensional photonic crystals. Using the Faraday model, different results were obtained for the responses of symmetric and asymmetric structures to magnetic fields for the right- and left-handed polarized dielectric constants. Our findings demonstrate that the defect mode is only seen in the CoSb₃-contained structure when a magnetic field between 0 and 1 T is used. For both symmetric and asymmetric Mg₂Si-contained structures, the peak was not apparent in the presence of magnetic field. The Drude model was used to analyze the temperature dependency of the defect mode for the structures mentioned above. For asymmetric and symmetric constructions, various frequencies and heights were found. The frequency of the CoSb₃ defect peak varies considerably as temperature rises from 100 to 300 K, whereas the Mg₂Si defect frequency remains unchanged. The asymmetric Mg₂Si structure at different temperatures did not exhibit any defect modes. The defect mode heights of all structures fall as the temperature rises.

An investigation of the transverse wave has been carried out in a structure of functionally graded material. The structure consists of layer and a semi-infinite medium. The layer is composed of a functionally graded magneto-electro-elastic material with a quadratic gradedness parameter. The semi-infinite medium is composed of functionally graded piezoelectric with a quadratic gradedness parameter. The interface between the layer and half-space is taken as loosely bonded and corrugated, whereas the upper boundary is assumed to be stress-free and corrugated. Moreover, the solutions for layer and half-space are obtained using the basic variable-separable method to reduce the partial differential equation to the ordinary differential equation. And ordinary differential equation solutions are obtained by using the WKB approximation technique. The solutions with boundary conditions lead to dispersion relations in the determinant form of two cases: electrically open and short. To know the impact of the parameter involved, a particular model consists of BaTiO₃–CoFe₂O₄ magneto-electro-elastic material layer and BaTiO₃ piezoelectric semi-infinite medium have been taken. Graphs of phase velocity versus wave number are plotted, which interpret the numerical outcomes physically.

Lasing of a wide-strip (100 µm) laser diode in an external resonator based on a planar waveguide structure with the Bragg grating is experimentally studied. The waveguide structure is made on Si substrates with a SiO₂:GeO₂ waveguide layer with the contrast of 2.4%. Spectral parameters of lasing and the far-field radiation distribution are investigated as a function of the relative position of the planes of the laser diode and external planar structure waveguides. It is shown that the higher-order transverse mode dominates in the lasing, and a substantial decrease in the spectral width of the radiation and stabilization of the spectrum are observed in the entire range of operating currents. Lasing in the radiationless and emitted waveguide modes of the external planar structure is demonstrated.

It is demonstrated how structured laser beams can be used to implement holographic optical tweezers for trapping and manipulating light-absorbing nano- and microparticles in the air. Two types of structured laser beams are investigated: polygon laser beams and superpositions of the Laguerre–Gauss modes with various carrier frequencies shifted relative to the propagation axis. The polygon laser beams generate arrays of optical bottle-beam traps, and the superpositions of the Laguerre–Gauss modes generate multiple light spots propagating along curved trajectories. The experiments have shown a possibility of optically trapping hundreds and thousands of airborne carbon nanoparticle agglomerations in a cuvette and passively guiding the trapped particles along a curved trajectory. The reported results can be used to develop laser manipulation systems for studying and transporting airborne nano- and microparticles.

The mechanisms of time-dependent impacts of classical nature (mechanical, magnetic, and electric) on quantum particles, including spin ones, have been theoretically analyzed. It is shown that the considered models allow two parametric mechanisms (Boltzmann and Pauli) for controlling the quantum states of particles. Methods for calculating the time–frequency and amplitude parametric gain regions have been defined and partially implemented for these mechanisms.

In this article, a method of depositing plasmonic particles on synthetic opal matrices was used for increasing the efficiency of laser-induced breakdown spectroscopy. The fundamental radiation, second and third harmonics of a picosecond neodymium laser were used to generate plasma. The dependences of the gain factor on the size of the laser spot, as well as on the concentration of silver particles, were obtained. The maximum signal amplification exceeding an order of magnitude was achieved at a wavelength of 1064 nm, corresponding to the localization of the plasmon resonance mode in the gap between closely spaced particles. Emission stability when using particles also increases at all laser wavelengths used. Conducted computer simulation confirmed the results of the experiment. High sensitivity of the method allows its use for monitoring even a small amount of impurity elements and their dynamics during the synthesis of photonic crystals, as well as the dynamics of the process of filling them with various materials during infiltration.

Consideration is given to the stationary mode of electromagnetic field oscillations in a resonator filled with a nanodisperse liquid suspension and excited by an external monochromatic wave. A general case of excitation of field oscillations in a resonator at an arbitrary ratio between the field and thermal energies of nanoparticles is investigated. It is shown that the increase in the field intensity in the resonator is nonlinear due to spatial redistribution of impurity dielectric particles and that the increase in the pump intensity may allow changing the resonator transmission and blocking radiation not associated with light absorption by the particles.

Treatment of antibodies using gradual technology implies a series of successive dilutions, accompanied by mechanical impacts, with subsequent saturation of lactose with the obtained solution. In comparison with intact lactose, the resulting products have increased emission in the RF frequency range from 50 MHz to 3.5 GHz.