Optical vortex generation from molecular chromophore arrays

The generation of light endowed with orbital angular momentum, frequently termed optical vortex light, is commonly achieved by passing a conventional beam through suitably constructed optical elements. This Letter shows that the necessary phase structure for vortex propagation can be directly produced through the creation of twisted light from the vacuum. The mechanism is based on optical emission from a family of chromophore nanoarrays that satisfy specific geometric and symmetry constraints. Each such array can support pairs of electronically delocalized doubly degenerate excitons whose azimuthal phase progression is responsible for the helical wave front of the emitted radiation. The exciton symmetry dictates the maximum magnitude of topological charge; detailed analysis secures the conditions necessary to deliver optical vortices of arbitrary order

Mechanism of fragmentation and atomization of molecular ions in gasdynamic transport cell

The fragmentation of molecular ions formed upon the electrospraying of a sample and transported through the gasdynamic system of a mass spectrometer equipped with an IESAP (Ion Extraction from Solution at Atmospheric Pressure) source has been experimentally studied. It is established that ion fragmentation in a Kantorowicz-Gray type cell takes place in the immediate vicinity of a skimmer port, apparently, as a result of collisions between ions (accelerated in an electric field) and stagnant gas. Molecular mechanisms of fragmentation are considered and it is concluded that this process can take place in a single ion-molecule collision even

Fraunhofer diffraction of a Laguerre-Gaussian laser beam by fork-shaped grating

In this article we present a theoretical study for Fraunhofer diffraction of a Laguerre-Gaussian laser beam with zeroth radial mode number and azimuthal mode number l by diffractive grating with embedded fork-shaped dislocations of integer order p. Analytical expressions describing the diffracted wave field amplitude and intensity distributions in the Fourier plane are deduced and analyzed. They are also followed by the vortex radii expressions.Comment: 13 pages, submitted for publishin

Direct generation of optical vortices

A detailed scheme is established for the direct generation of optical vortices, signifying light endowed with orbital angular momentum. In contrast to common techniques based on the tailored conversion of the wave front in a conventional beam, this method provides for the direct spontaneous emission of photons with the requisite field structure. This form of optical emission results directly from the electronic relaxation of a delocalized exciton state that is supported by a ringlike array of three or more nanoscale chromophores. An analysis of the conditions leads to a general formulation revealing a requirement for the array structure to adhere to one of a restricted set of permissible symmetry groups. It is shown that the coupling between chromophores within each array leads to an energy level splitting of the exciton structure, thus providing for a specific linking of exciton phase and emission wavelength. For emission, arrays conforming to one of the given point-group families’ doubly degenerate excitons exhibit the specific phase characteristics necessary to support vortex emission. The highest order of exciton symmetry, corresponding to the maximum magnitude of electronic orbital angular momentum supported by the ring, provides for the most favored emission. The phase properties of the emission produced by the relaxation of such excitons are exhibited on plots which reveal the azimuthal phase progression around the ring, consistent with vortex emission. It is proven that emission of this kind produces electromagnetic fields that map with complete fidelity onto the phase structure of a Laguerre-Gaussian optical mode with the corresponding topological charge. The prospect of direct generation paves the way for practicable devices that need no longer rely on the modification of a conventional laser beam by a secondary optical element. Moreover, these principles hold promise for the development of a vortex laser, also based on nanoscale exciton decay, enabling the production of coherent radiation with a tailor-made helical wave front

Variations on the Deuteron

We consider few problems which are related to the deuteron and have simple analytical solution. Relation is found between the deuteron electric quadrupole moment and the $np$-scattering amplitude. The degree of circular polarization of photons is calculated for the radiative capture of longitudinally polarized thermal neutrons. The anapole, electric dipole and magnetic quadrupole moments of the deuteron are calculated.Comment: 14 pages, late

Optical spin-to-orbital angular momentum conversion in inhomogeneous anisotropic media

We demonstrate experimentally an optical process in which the spin angular momentum carried by a circularly polarized light beam is converted into orbital angular momentum, leading to the generation of helical modes with a wavefront helicity controlled by the input polarization. This phenomenon requires the interaction of light with matter that is both optically inhomogeneous and anisotropic. The underlying physics is also associated with the so-called Pancharatnam-Berry geometrical phases involved in any inhomogeneous transformation of the optical polarization

Competition-based model of pheromone component ratio detection in the moth

For some moth species, especially those closely interrelated and sympatric, recognizing a specific pheromone component concentration ratio is essential for males to successfully locate conspecific females. We propose and determine the properties of a minimalist competition-based feed-forward neuronal model capable of detecting a certain ratio of pheromone components independently of overall concentration. This model represents an elementary recognition unit for the ratio of binary mixtures which we propose is entirely contained in the macroglomerular complex (MGC) of the male moth. A set of such units, along with projection neurons (PNs), can provide the input to higher brain centres. We found that (1) accuracy is mainly achieved by maintaining a certain ratio of connection strengths between olfactory receptor neurons (ORN) and local neurons (LN), much less by properties of the interconnections between the competing LNs proper. An exception to this rule is that it is beneficial if connections between generalist LNs (i.e. excited by either pheromone component) and specialist LNs (i.e. excited by one component only) have the same strength as the reciprocal specialist to generalist connections. (2) successful ratio recognition is achieved using latency-to-first-spike in the LN populations which, in contrast to expectations with a population rate code, leads to a broadening of responses for higher overall concentrations consistent with experimental observations. (3) when longer durations of the competition between LNs were observed it did not lead to higher recognition accuracy

DIFFERENTIATION OF NK CELLS. A LOOK THROUGH THE PRISM OF TRANSCRIPTION FACTORS AND INTRACELLULAR MESSENGERS

All lymphoid cells are referred to as an innate or adaptive immunity unit in terms of the mechanisms of performing immune reactions. The functional activity of natural killer (NK) cells is not associated with pre-activation processes resulting from contact with antigen, rearrangement of antigen-recognition receptor genes, and clonal proliferation. In this regard, NK cells are traditionally referred to as cells of innate immunity. Previously, it was believed that NK cells represent the only population of innate immunity lymphoid cells, but, more recently, there has been increasing evidence in the literature concerning existence of different populations of these cells, thus serving a basis for isolating a common cluster called Innate Lymphoid Cells (ILC). According to the ILC classification, NK cells are classified as the first group of innate lymphoid cells according to their overall functional characteristics, as well as contribution of the T-bet transcription factor to their differentiation. Complexity, multistage and partially nonlinear character of NK cell differentiation are associated with influence of the cellular microenvironment, consistent expression of transcription factors and activation of various intracellular signaling pathways in NK cells. The review considers positioning of NK cells in the ILC classification, the main transcription factors involved in NK cell differentiation. The authors are seeking for generalization of the major routes of intracellular signal transmission in NK cells depending on their activation by cytokines located in the cellular microenvironment and affecting NK cells. The decidual NK cells during pregnancy represent a special object of NK cell differentiation. Stromal cells, trophoblast cells and macrophages are present in the decidua, in addition to NK cells. The review concerns a special case of microenvironmental effects upon expression of transcription factors and activation of NK intracellular messengers, while considering trophoblast cells an example of such influences. The recently discovered variety of NK cells, induced by the microenvironment in the course of their differentiation, requires further study