High-quality optical Fano resonances, which exist in a spherical dielectric microparticle in the spatial configurations of the whispering-gallery like modes (WGMs) and recently are referred to as the “super-resonances”, possess extremal sensitivity not only to the micro-cavity size and shape but also to the optical properties of the particulate material. The increase in the power of light radiation coupling into a WGMs can lead to the manifestation of strong optical nonlinearity of the resonator material due to the cubic nonlinearity (optical Kerr effect) and generation of free electron plasma in certain regions of the spherical microcavity. In fact, an optically linear medium of the resonance cavity transforms into a Drude-Kerr-type medium with a strong dependence on input laser intensity. With the help of the finite-elements numerical simulations, we theoretically analyze the transformations of the resonant contour for a number of high-quality WGMs-like excited in a lanthanum-glass microsphere exposed to an optical radiation of different intensity. We show that in a certain input intensity range, the competition of Kerr and plasma optical nonlinearities can stop and even reverse the Stokes shift of the super-resonance observed in a pure Kerr medium. Additionally, optical ionization and plasma generation within the mode volume significantly reduce the strength of the magnetic super-resonance and lead to its spoiling and frequency splitting. Our findings pav the way for an all-optical approach for the obtaining the strong magnetic fields of the order of tens Tesla at relatively moderate laser intensities without the use of structured laser beam.

Binary Fresnel zone plates (ZP) are one of the most frequently used focusing elements of inplane optical schemes in micro- and nanophotonics. With a decrease in the diameter and focal distance of the ZP to meso-wavelength sizes, the parameters of the focusing region begin to be significantly influenced by features of the ZP design (material, thickness, relief depth). The spatial structure of the focal spot formed in the near-field is investigated by the numerical finite elements (FEM) simulations of the transmission of a plane optical wave through a mesoscale binary phase ZP. We show that there is a range of optimal etching depths of the ZP ridges and optimal thicknesses of the plate substrate, at which the best focusing of the incident optical wave is realized in terms of the maximum field intensity and the minimum size of the focal spot. In addition, a concept of a super-focusing binary phase ZP with an immersion layer in the form of a truncated cone fabricated of ZP material is proposed, which makes it possible to focus the circularly polarized light wave into a subdiffraction region with a half-width of about "lambda"/2n (n is the ZP refractive index).

The characteristics of the multiple filamentation domain of femtosecond laser pulses in air have been estimated based on the single filamentation model. The diffraction-ray model is considered as the single filamentation model. It is based on representation of a laser beam by a set of diffraction-ray tubes nested into each other that do not intersected in space and do not exchange by their energies. In this situation, changes in the tube shapes and cross sections during beam propagation demonstrate the effect of physical processes that occur with radiation in the medium. It is shown that this model is efficient for interpreting experimental results. In particular, it has been demonstrated that the radius of small-scale intensity inhomogeneities in the profile of a centimeter laser beam forming the multiple filamentation domain of subterawatt femtosecond laser pulses is several millimeters. The power in these inhomogeneities varies from several units to several tens of gigawatts. Telescoping the initial laser beam that caused an increase in its radius also increased sizes of the initial smallscale intensity inhomogeneities and decreased the power contained in them. As a result, the coordinate of the filamentation onset is shifted along the propagation path from the laser pulse source. The lengths of the filaments and their number increase with the peak beam power.

We propose and discuss main properties of a new concept of an all-optical dielectric two-channel wavelength-selective switch based on the photonic hook effect. A prototype of such a de-vice based on dielectric microstructures with broken symmetry of both geometric shape and optical properties without the use of micromechanical devices or nonlinear materials is considered. Due to the unique property of the photonic hook to change its curvature depending on the wavelength of illuminating light, this switch is a promising candidate for the implementation of optical switching in modern optoelectronics and miniature devices "on a chip". Based on numerical FDTD simulations, it is shown that the optical isolation of switched channels for a switch with linear dimensions of about (6 * "lambda")3 based on a Janus particle can reach about 18-20 dB in the wavelength range of 1.5 – 1.9 microns.

The results of a theoretical study of the propagation of femtosecond pulses of a Ti:Sa laser under normal dispersion conditions in air are presented. The use of the diffraction-beam tube method for the analysis of numerical solutions of the nonlinear Schrödinger equation in a dispersion medium with Kerr-plasma nonlinearity made it possible to determine the basic regularities of femtosecond laser pulses self-focusing and filamentation in air at various pulse lengths, initial beam radius, and peak powers. It is shown that in the case of the group velocity dispersion influence with an increase in the initial laser beam radius, the filamentation breaks down even at large supercritical powers. It is shown that with an increase in the dispersion distortions of the pulse the radius of the energetically replenishing diffraction beam tube, the angular divergence of the post-filamentation light channel, and the nonlinear focus coordinate normalized to the Rayleigh length for the central time layers of the laser pulse and the integral picture are increasing.

Specific spatially-localized optical field structure, which is often referred to as a photonic nanojet (PNJ), is formed in the near-field scattering area of non-absorbing dielectric micron-sized particle exposed to an optical radiation. By virtue of the finite-difference time-domain technique we numerically simulate the two-dimensional array of PNJs created by an ordered single-layer microassembly of glass microspheres immersed in a transparent polymer matrix. The behavior of the main PNJ parameters (length, diameter, and intensity) is analyzed subject to the immersion depth of the microparticles and cooperative interference effects of the neighboring microspheres. We show that depending on microassembly configuration, the PNJ quality can be significantly improved; in particular, the PNJ spatial resolution better than lambda/5 can be achieved. (C) 2017 Elsevier Ltd. All rights reserved.

Self-focusing and filamentation of high-power pulsed laser radiation along a spectrally selective absorbing air path are numerically simulated in three spectral ranges centered at 0.8, 3.9, and 10.6 mu m. A detailed comparative analysis of the main pulse parameters in the filamentation area is performed to examine the potential of various laser sources for atmospheric optics. We found that the radiation of mid-IR lasers (3.9 and 10.6 mu m) forms the longest filamentation region and the widest supercontinual spectrum in comparison with near-IR radiation. Filamentation of the 3.9 mu m laser pulse results in the best spatially continued plasma channel, while the 10.6 mu m pulse retains the widest spectral composition under the conditions of strong molecular absorption in the atmosphere. (C) 2017 Optical Society of America

A single filamentation of femtosecond gigawatt laser radiation with a millimeter-size aperture upon collimated and sharply focused propagation in atmospheric air at 800 nm and 400 nm wavelengths is studied both theoretically and experimentally. The influence of beam initial radius on the parameters of the forming filament is analyzed. Three filament parameters, namely, start coordinate, filament length, and longitudinal continuity are considered. We report that unlike Marburger's formula the single filamentation onset reveals marked nonquadratic dependence on the laser beam radius providing the same initial pulse power. Additionally, for sharply focused radiation the minor dependence of the filament length on the laser beam diameter at the constant initial pulse intensity was experimentally revealed.

We numerically simulated the nonlinear propagation of high-power subpicosecond laser radiation at 10.6 mu m carrier wavelength in air under conditions of pulse Kerr self-focusing and single and multiple filamentation. For the first time, to the best of our knowledge, we show that in contrast to the well-known femtosecond pulse filamentation in the near-infrared domain (800 nm), the self-action of mid-infrared radiation is characterized by the formation of millimeter-wide filaments accompanied by nearly continuous along the propagation direction and elongated plasma columns. The physical cause is the change of the air ionization regime by the CO2-laser pulse in favor of impact ionization and electron avalanche development. This alters the character of plasma influence on the laser radiation by enhancing the role of physical processes attributed to the liberated hot electrons. (C) 2014 Optical Society of America

We present a new outlook on the problem of ultrashort laser pulse self-focusing and filamentation when propagating in air. Two previously known qualitative physical models of optical pulse filamentation scenario, the dynamic multiple focusing, and the wave-guiding models, are considered and partially revisited. In terms of the averaged (effective) laser beam radius, the filament is treated as a net product of layer-by-layer (in time) self-focusing of separate temporal pulse slices. By means of the developed time-averaged diffraction ray tracking technique, the crucial role of the diffraction effects in the formation of a light filament and next following a low-divergent light channel near the beam axis is revealed.

The generic scenario of intense femtosecond laser pulse propagation in the air from the viewpoint of evolution of its integral effective parameters (energy transfer coefficient, effective radius, effective duration, limiting angular divergence) is considered. The analysis of variation of the effective parameters along the propagation path in the single and multiply filamentation scenarios based on numerical calculations is presented. It is shown that the process of self-action of the ultrashort radiation is characterized by the formation in a medium of the nonlinearity layer, after which optical pulse propagates quasi-linearly with the limiting angular divergence that depends mainly on initial pulse power. The effective pulse temporal duration and the effective beam radius increase after the passage through the nonlinearity layer, and their values are mostly determined by the initial beam power also. The coefficient of energy transmission of femtosecond laser radiation is lower than in the linear medium and has a tendency to decrease with the increase of the pulse power.