Physics of Wave Phenomena最新文献

A new type of diode laser with a scalable (fundamentally unlimited) aperture for the output optical beam has been proposed and calculated. Such an aperture can be implemented due to the use of a vertical cavity with one of the mirrors in the form of a surface diffraction grating. The threshold current density and differential efficiency of the proposed laser are calculated for the material parameters characteristic of the InGaAs/AlGaAs heterostructure and the spectral range at 0.98 µm.

Computer simulation of two-dimensional colloidal systems, in which interactions between particles are induced and controlled by an external rotating magnetic field, has been performed. The effective interaction potential of particles, along with the conventional pair potential, includes also three-particle interaction. It is shown that one of the parameters of the potential—field precession angle—radically changes the character of particle interaction and the phase diagram. In particular, at small angles the system behaves like a two-dimensional system with a purely repulsive soft-disk potential, whereas at large angles it behaves like a generalized Lennard-Jones system with the (nm)-potential; the presence of the three-particle part of potential reduces the temperature of the gas–liquid critical point. At intermediate field precession angles the phase diagram contains melting lines of triangular crystals of high and low density, between which a phase with a Kagome lattice was found. Our results serve an important guide for future experiments and simulation of colloidal systems, as well as for solving many problems in the fields of “soft” matter, physical chemistry, chemical physics, photonics, and materials science

We suggest and describe the protocol of measurements providing completely probabilistic representation of all parameters of polarization biphoton qutrits, i.e. providing explicit expressions for all parameters of qutrits via the probabilities of getting those or other results in measurements.

The content of H₂O spin isomers in saturated vapor during its fast evaporation from the surface of water in a cell at room temperature has been analyzed. The experiment was performed using the two-compartment scheme of simultaneous fast laser analysis of the concentration ratio of H₂O ortho- and para-isomers in saturated vapor in two analytical cells. One of these cells cointained water and its saturated vapor. The other was previously evacuated, and saturated vapor from the first cell was fed to it. Simultaneous analysis of the relative content of ortho- and para-water molecules during gas probe sampling, which lasted about 0.8 s, was performed with a rate of 10 measurements per second using a two-channel spectrophotometer based on tunable diode lasers (TDLs). The spectral range near 7355 cm^–1, where the ortho- and para-Н₂О absorption lines are closely located, was chosen for analysis. During the fast evaporation, which accompanied saturated vapor sampling, the evaporating vapor was found to be enriched with ortho-H₂O isomer, whose content amounted to ~20% of the equilibrium value 3 : 1. An important fact is that this result is indicative of possible enhanced mobility and the absence of hydrogen bonds for some of ortho-Н₂О molecules in the surface water layer, which is consistent with the known fact that water vapor transmitted through porous materials becomes enriched with ortho-H₂O isomers.

To reduce the ohmic loss of the encoding metasurface and achieve continuous control of the scattering angle larger than 70°, we numerically study all dielectric reflective metasurface in the mid-infrared waveband. Free control of the deflection angle of the far-field scattered beam is achieved. The unit structure designed consists of the Ge₂Sb₂Te₅ phase change material and the substrate. The phase difference between each two-unit structures is 90° and has high reflectivity in the working band. We can arrange the four units to construct metasurfaces with different coding sequences and perform Fourier convolution operations on the metasurfaces with different coding sequences to obtain flexible control of the reflected beam. The reflection characteristics of the coding sequence in the crystalline and amorphous states of the Ge₂Sb₂Te₅ phase change material are demonstrated. The abnormal reflection angle phenomenon of the simulated structure was theoretically analyzed.

We carried out a Raman study of a series of poly(L-lactide) (PLLA) samples annealed for different periods of time and therefore having different crystallinity degree. We compared the results with our recent study of the series of poly(L-lactide-co-ε-caprolactone) (PLCL) copolymers with the ε-caprolactone (CL) content ranging from 5 to 30 mol %. X-ray diffraction (XRD) analysis showed that the crystallinity degree of the analyzed PLLA-based materials is in the range of 0–86%. We suggest using the ratio of the peak intensities of the PLLA Raman bands at 411 and 874 cm^–1 to evaluate the crystallinity degree of PLLA homopolymers as well as PLLA blocks in the PLCL copolymers. This ratio does not depend on the CL content in the copolymers, it strongly depends on the crystallinity degree of PLLA (PLLA blocks in the PLCL copolymers) and it is a linear function of the crystallinity degree, measured by XRD analysis. We carried out quantum chemical calculations of the optimized geometries and Raman spectra of PLLA oligomers in the conformation of helix 10₃ with the number of monomeric units from 5 to 12. The results of the calculations revealed that the ratio of the intensities of the bands at 411 and 874 cm^–1 weakly depends on the oligomer length for the number of the PLLA monomeric units more than 7.

The results of theoretical investigation of magnetooptical properties of CoPt-based nanostructures are presented. Within the effective medium method, namely, the symmetrized Maxwell Garnett approximation, spectral dependences of the transverse effect are calculated for ferromagnetic granules with allowance for the size effect. The simulation showed good agreement of the experimental and theoretical data in the visible region of the spectrum.

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.