Andrey A. Morozov

Is the pentaquark doublet a hadronic molecule

A recently announced discovery by LHCb of a doublet of overlapping pentaquark resonances poses a question of what can be the origin of this doublet structure. We attract attention to the fact that such degeneracy could naturally arise if constituent “baryon” and “meson” were in the colored, rather than colorless states. This is an appealing possibility, also because in such a case the pentaquark state would be no less “elementary” than the other hadrons, and would provide a chance for essentially new non-Abelian chemistry.

Narrowing of a light spot at diffraction of linearly-polarized beam on binary asymmetric axicons

AbstactTo compensate widening of the central light spot which inevitably arises at linear polarization of a beam illuminating high-numerical-aperture axicon we propose to introduce an asymmetry in axicon structure. Experimental research of diffraction of Gaussian beam by three types of binary microaxicons with the period close to wavelength was carried out by means of near-field microscope. Diffractive optical elements with the period of 500 nanometers and various height of a microrelief have been fabricated by e-beam lithography. Narrowing of a central light spot formed by asymmetric microaxicons was experimentally confirmed. Overcoming of the diffraction limit (down to FWHM = 0.32λ) was observed in a near zone.

On 6 j -symbols for symmetric representations of U q (su N )

Explicit expressions are found for the 6j symbols in symmetric representations of quantum suN through appropriate hypergeometric Askey–Wilson (q-Racah) polynomials. This generalizes the well-known classical formulas for Uq(su2) and provides a link to conformal theories and matrix models.

Geodesic deviation and particle creation in curved spacetimes

A quantum mechanical picture, relating accelerated geodesic deviation to creation of massive particles via quantum tunneling in curved background spacetimes, is presented. The effect is analogous to pair production by an electric field and leads naturally to production of massive particles in de Sitter and superluminal FRW spacetimes. The probability of particle production in de Sitter space per unit volume and time is computed in a leading semiclassical approximation and shown to coincide with the previously obtained expression.

Formation of high-frequency two-dimensional interference patterns of surface plasmon polaritons

The formation of high-frequency two-dimensional interference patterns of surface plasmon polaritons in a structure consisting of four diffraction gratings with one-dimensional periodicity in a metallic film has been studied numerically and experimentally. It has been shown that change of linear polarization of the incident radiation to its circular polarization makes it possible to reduce the period of the formed pattern at a fixed wavelength. A similar change in the form of the pattern can be achieved by introducing an equivalent shift to the geometry of the structure.

On the Hopf-Induced Deformation of a Topological Locus

We provide a very brief review of the description of colored invariants for the Hopf link in terms of characters, which need to be taken at a peculiar deformation of the topological locus, depending on one of the two representations associated with the two components of the link. Most important, we extend the description of this locus to conjugate and, generically, to composite representations and also define the “adjoint” Schur functions emerging in the dual description.

Various superpositions of Bessel beams for capture and controlled rotation of microobjects

The authors present a technique for modulation laser beams into beams with special properties, capable of trapping and rotating objects of micro-size. There are two approaches covered: the first one utilizes zero-order Bessel beams superposition for light tubes shaping, and the second one forms Bessel beams superpositions with diffractional optical elements with spatially partitioned topological charge or, alternatively, with vortex axicones. The authors also cover micro-mechanical object manufacturing, optimized for rotating in vortex Bessel beams superposition. Results of numerical simulations and experimental data are presented and then discussed.

Multifocal diffractive lens generating several fixed foci at different design wavelengths

We propose a method for designing multifocal diffractive lenses generating prescribed sets of foci with fixed positions at several different wavelengths. The method is based on minimizing the difference between the complex amplitudes of the beams generated by the lens microrelief at the design wavelengths, and the functions of the complex transmission of multifocal lenses calculated for these wavelengths. As an example, a zone plate generating three fixed foci at three different wavelengths was designed, fabricated, and experimentally investigated. The proof-of-concept experimental results confirm the formation of foci with fixed positions at the design wavelengths. The obtained results may find applications in the design and fabrication of novel multifocal contact and intraocular lenses with reduced chromatic effects.

Experimental study of optical characteristics of a satellite-based Offner hyperspectrometer

A hyperspectrometer based on the Offner scheme was investigated. Spectral characteristics were studied and calibrated using a standard spectrometer. As a result of estimating the deviations of the spectra of the imaging hyperspectrometer and the reference spectrometer, calibration coefficients were obtained. The reflectance spectra of beets, onions and potatoes under natural solar illumination were experimentally obtained. Based on the analysis of hyperspectral imaging data, an analysis of the distribution of vegetative indices and, in particular, moisture content, was carried out. Analysis of histograms of moisture content index distribution was carried out.

On-chip near-wavelength diffraction gratings for surface electromagnetic waves

In the present work, on-chip dielectric diffraction gratings for steering the propagation of surface plasmon polaritons (SPP) are theoretically, numerically and experimentally studied. The investigated plasmonic gratings consist of dielectric ridges located on the SPP propagation surface (on the metal surface). In contrast to Bragg gratings, at normal incidence the periodicity direction of the grating is perpendicular to the SPP propagation direction. The studied gratings are designed using a simple plane-wave grating model and rigorously simulated using the aperiodic Fourier modal method for numerical solution of Maxwell’s equations. In particular, plasmonic grating-based beam splitter with subwavelength footprint in the propagation direction is presented. Along with the theoretical and numerical results, proof-of-concept experimental results are presented. The investigated grating-based plasmonic gratings were fabricated from resist on a silver film using electron beam lithography and characterized using the leakage radiation microscopy technique. The obtained experimental results are in good agreement with the performed numerical simulations. The proposed on-chip gratings may find application in the design of systems for optical information transmission and processing at the nanoscale.