Analytical expressions to describe nonparaxial diffraction of vortex laser beams during their propagation in free space are obtained. The beams excited by radially polarized TM0m (m = 1, 2, 3) modes of a dielectric waveguide resonator of a terahertz laser, which interact with a spiral phase plate with an arbitrary topological charge (n) are considered. The simulation is performed using the Rayleigh-Sommerfeld integral theory. It is shown that a phase plate with topological charges n = 1, 2 forms a field in the Fresnel zone, in which an azimuthal component appears. In this case, preservation of the radial and longitudinal components of the field is observed and the contribution of the longitudinal component to the total beam power remains insignificant. For a phase plate charge n = 1, the maximum of the field intensity is located on the axis, whereas the field distribution for n = 0 and n = 2 becomes ring-shaped. The maximum values of the field intensity are observed at a charge n = 1, while they decrease at n = 2. Phase distributions of the field transverse components of vortex laser beams are visualized. At a topological charge n = 1, they become a one-lobe helical structure, and a two-lobe structure with more pronounced helical twists of the azimuthal component for all the studied modes is observed at n = 2.
This review article describes in a concise form some of the latest achievements in semiconductor physics related to the topological and quantum properties of electron dynamics, in particular, in strong electric fields; new concepts in electronics based on the quantum degrees of freedom of electrons, which have led to the emergence of new branches distinct from traditional charge-based electronics. The recent emergence of picosecond-toattosecond time-resolved and scanning spectroscopy has prompted the development of quantum theory describing the detailed high-frequency behavior of electrons on very short temporal and spatial scales, of the order of a few interatomic distances. In fact, such a precise spatiotemporal dynamical picture represents, in a sense, the anatomy of electrons in the periodic potential of a crystal lattice. Specifically, our attention is focused on the following issues that have been actively discussed in leading scientific journals over the past decade: the Berry phase, orbitronics, Zitterbewegung (trembling motion), and effective mass dynamics. Although several specialized reviews already have devoted to the addressed topics, we believe that such review digest including most recent references can help the readers, including authors of SPQEO, to get more information about current trends in the modern semiconductor theory and applications.
Indotetracarbocyanines belong to a family of long cyanine dyes that easily change molecular shape from symmetric cyanine-like to asymmetric polyene state. Multiple factors affect the conformations of such molecules and therefore influence their photoluminescent emission. In this paper, we investigated the photophysical behavior of indotetracarbocyanine dyes in various solvent environments and in mixtures with singlewalled carbon nanotubes. The results revealed concentration-, aging-, and solvent-polarity dependent spectral features of such dyes, allowing us to establish key mechanisms for emission tuning. The spectral changes have been associated with symmetry-dependent molecular conformations of indotetracarbocyanines and their ability to interact with carbon nanotube surfaces. New emission bands emerge in the photoluminescence spectra due to dye-nanotube interactions, mediated by it-it stacking and electrostatic effects. This behavior is consistent with adsorption-induced aggregation of the dye on the nanotube surface and with the formation of new photoinduced emitting states.
The effect of the substrate material combined with a polytetrafluoroethylene (PTFE) overlayer on the sensitivity of optical sensors based on surface plasmon resonance (SPR) in the Kretschmann geometry has been investigated. The experiments were performed at a fixed excitation wavelength of surface plasmons using a gold plasmonsupporting layer. The testing of the sensor elements was carried out by cyclic displacement of ambient air by inert helium in the flow cell. A comparative analysis of the characteristics of SPR sensors on substrates made of F1 optical glass and styrene-acrylonitrile (SAN) polymer was carried out in both the presence and absence of a PTFE overlayer on the gold film surface. It was established that replacing the glass substrate with the polymer (SAN) causes an increase in sensitivity from 45.8 to 48.1 deg/RIU due to a decrease in the refractive index; however, it doubles the figure of merit (FOM) from 26.2 to 50.1 RIU-1. The application of the PTFE overlayer for both sensor types led to an increase in sensitivity: from 45.8 to 74.4 deg/RIU for the glass substrate, and from 48.1 to 52.1 deg/RIU for the polymer substrate. In addition to enhanced sensitivity, the use of the polymer material allows for reducing the cost of the final product, simplifying the stages of precision surface treatment. An additional advantage is the narrowing of the resonance curves, which significantly improves the accuracy of the resonance angle registration.
A simulation algorithm has been developed and geometric parameters of plane-focusing lenses for concentrator solar energy systems with Si photoconverters have been calculated. These lenses form a homogeneous image in the focal plane, so they are promising for use in such systems and allow minimizing thermal and electrical losses in solar modules caused by non-uniform illumination of the photoconverter surface. A technology of manufacturing stamp-matrixes by diamond microcutting has been developed. Based on the simulation results, a number of plane-focusing lens samples have been formed by thermopressing technique using metal matrices. The manufactured samples of square-shaped specialized transforming microprismatic structures have been experimentally investigated using a collimated laser beam.
