Optics and Spectroscopy最新文献

The paper considers collisions involving spin polarized alkali Na and Cs atoms in the ground state. The complex cross sections for spin exchange and the elastic scattering cross sections of the considered atoms are calculated in the energy range from 10^–4 to 10^–2 a.u.

A comparison of the generation efficiency of short pulses with coherent and standard passive (incoherent) mode locking with a saturable absorber is made on the basis of numerical simulations. The advantage of the coherent mode locking in comparison to the standard mode locking in lasers with a saturable absorber is shown. Coherent mode locking in two-section lasers is based on the coherent interaction of the radiation with the absorbing and amplifying media. It allows the generation of ultrashort laser pulses with a duration shorter than the polarisation relaxation time T₂ of the absorbing and amplifying media. In conventional lasers with standard (incoherent) passive mode locking with a saturable absorber, the interaction of the laser pulses with the absorbing and amplifying media is incoherent and the duration of the generated pulses is always limited by the polarization relaxation time T₂ of the absorber and amplifier.

Bismuth tantalum pyrochlores doped with iron and magnesium atoms were obtained thermally stable up to a temperature of 1140°C: Bi₂Mg_xFe_{1 – x}Ta₂O_{9.5 – Δ} (x = 0–1). The effect of Fe and Mg codoping on their crystal structure has been studied. The unit cell parameter of solid solutions increases uniformly from 10.4871 (2) Å (x = 0) to 10.54607 Å (x = 1). According to the XPS and NEXAFS spectroscopy data, it was found that the ions in these solid solutions are in the charge states Bi(+3), Mg(+2), Fe(+3), Ta(+5 – δ). The dopant atoms iron and magnesium are introduced into the positions of the tantalum atom without distorting the symmetry of the crystal lattice.

A circuit design of a fiber endoscope is described that allows monitoring of hard-to-reach cavities and other partially transparent and/or reflective objects into which it is possible to pass a thin fiber bundle.

Spectral properties of composite materials based on matrices of high-silica porous glasses activated by silver ions and lanthanum ions have been investigated. The optical density spectra (270–900 nm) and infrared transmittance spectra (11 000–9000 and 9000–4000 cm^–1) of composite materials of different compositions subjected to heat treatment according to one of three modes (120, 500 and 800°C) have been considered. The synthesized composite materials were investigated by X-ray powder diffraction method and energy-dispersive X-ray spectroscopy. The analysis of optical spectra permitted to identify the formation of molecular clusters, clusters, dimers and silver nanoparticles, as well as absorption bands related to charge transfer O²⁺ → La³⁺ (282, 285, 300 nm) and to lanthanum nanoparticles (282, 285 nm) under different conditions of synthesis of composite materials. It was found that the change in the mode of thermal treatment of composites leads to changes in the IR spectra of composites, and the change in their composition leads to the appearance of additional bands associated with the oxygen atom of the OH-group, which can coordinate with several neighboring lanthanum atoms.

The mathematical modeling of operating regimes of parametric THz devices based on graphene metamaterials (graphene‒dielectric periodic structures (GDPSs)) has been carried out by solving a nonlinear 3D diffraction problem for Maxwell’s equations in the projection integral form. Using an algorithm for computing bifurcation points of the nonlinear Maxwell operator, the threshold pump wave amplitudes have been calculated at which an unstable mode of the parametric excitation of electromagnetic waves occurs in GDPS-based THz device.

Using the CST Microwave Studio 2023, models of plasmonic graphene antennas (PGAs) with excitation by using discrete and waveguide ports by incident TEM-waves of S- and P-polarization have been constructed. The characteristics of rectangular and square PGAs with dielectric and metallized substrate: scattering matrix elements, radiation patterns for various graphene parameters and chemical potential values have been calculated.

Computational algorithm for determining the descriptor of autonomous blocks with virtual Floquet channels (MFABs) containing magnetically functionalized carbon nanotubes (MFCNTs) with encapsulated magnetic nanoparticles is developed. The algorithm is based on solving the 3D problem of diffraction for the Maxwell’s equations together with the Landau–Lifshitz equation by applying the Galerkin projection method. Electrodynamic calculation of the complex wavenumbers of the longitudinal and transverse waves propagating in the 3D MFCNT arrays as functions of magnitude of the bias field in the millimeter and terahertz frequency ranges is carried out based on the characteristic equation by means of the developed computational algorithm for calculation of the MFAB conductivity matrix.

The possibility of combining solid-phase extraction of natural catecholamines (adrenaline, norepinephrine, and dopamine) on a microcolumn filled with hypercrosslinked polystyrene with their subsequent spectrophotometric or solid-phase spectroscopic determination in an eluate using gold nanorods or their nanocomposites with polyurethane foam has been investigated. The desorption of catecholamines from hypercrosslinked polystyrene by various eluents has been studied. It has been shown that the quantitative elution of all three catecholamines is achieved using 6 M acetic acid, which as an eluent is well combined with the proposed determination options. The features of a dynamic sorption extraction of catecholamines from urine and blood serum have been described. It allows you to reduce the influence of the matrix components and increase the analysis sensitivity by concentrating. The average concentration coefficient is 10–56 with sample volumes of 10–300 mL. The developed methods make it possible to determine catecholamines in urine at the level of their normal content.

The article has considered the possibility of using the developed original method for estimating the parameters of photovoltaic converters (PVCs) both during the output control at the production site and during the input control carried out before the assembly and installation of solar panels. A comparison of products from different manufacturers has been performed. It has been shown that the proposed method is effective and can be recommended for use by specialized enterprises.