Gradient Optics of subwavelength nanofilms

Propagation and tunneling of light through subwavelength photonic barriers, formed by dielectric layers with continuous spatial variations of dielectric susceptibility across the film are considered. Effects of giant heterogeneity-induced non-local dispersion, both normal and anomalous, are examined by means of a series of exact analytical solutions of Maxwell equations for gradient media. Generalized Fresnel formulae, visualizing a profound influence of gradient and curvature of dielectric susceptibility profiles on reflectance/transmittance of periodical photonic heterostructures are presented. Depending on the cutoff frequency of the barrier, governed by technologically managed spatial profile of its refractive index, propagation or tunneling of light through these barriers are examined. Nonattenuative transfer of EM energy by evanescent waves, tunneling through dielectric gradient barriers, characterized by real values of refractive index, decreasing in the depth of medium, is shown. Scaling of the obtained results for different spectral ranges of visible, IR and THz waves is illustrated. Potential of gradient optical structures for design of miniaturized filters, polarizers and frequency-selective interfaces of subwavelength thickness is considered

Hydrodynamic flow of expanding Bose-Einstein condensates

We study expansion of quasi-one-dimensional Bose-Einstein condensate (BEC) after switching off the confining harmonic potential. Exact solution of dynamical equations is obtained in framework of the hydrodynamic approximation and it is compared with the direct numerical simulation of the full problem showing excellent agreement at realistic values of physical parameters. We analyze the maximum of the current density and estimate the velocity of expansion. The results of the 1D analysis provides also qualitative understanding of some properties of BEC expansion observed in experiments.Comment: 5 pages, 3 figures, RevTeX4. To appear in Physical Review

Nonlinear broadband doubling of the extraordinary wave frequency in inhomogeneous magnetoactive plasma

The nonlinear resonance doubling of radio wave frequencies in inhomogeneous plasma is studied as applied to the ionosphere under the conditions of the phase synchronism between an extraordinary pump wave and its second harmonic. The synchronism is not related to plasma resonances, but is determined by the magnetic field and plasma electron density in the transparency region. The generation efficiency of the second harmonic of a transversely propagating wave is calculated for a wide frequency band lying higher than the lower hybrid resonance frequency. It is shown that this effect is physically analogous to the generation of the second harmonic of laser radiation in a nonlinear crystal. The generation efficiency of the second harmonic is determined for inhomogeneous ionospheric plasma in which the synchronism condition is satisfied in a limited frequency range. It is shown that this effect can be used for remote nonlinear diagnostics of the upper ionospheric plasma, in which the characteristic size of the synchronism region can reach several kilometers. It is proposed to use a combination of satellite and ground-based ion probes in experiments on transionospheric probing. Even if the frequency of the wave emitted from the satellite is lower than the critical frequency in the ionosphere, the frequency of its second harmonic can exceed the critical frequency, so that it can be recorded by a ground-based ion probe or a specially designed receiver. The reflected second-harmonic signal can also be detected at the satellite by using a broadband radio-frequency spectrometer. © 2014 Pleiades Publishing, Ltd

OPTICS OF SUBWAVELENGTH GRADIENT NANOFILMS

International audiencePropagation and tunneling of light through subwavelength photonic barriers, formed by dielectric layers with continuous spatial variations of the dielectric susceptibility across the film are considered. Effects of giant heterogeneity-induced non-local dispersion, both normal and anomalous, are examined by means of a series of exact analytical solutions of the Maxwell equations for gradient media. Generalized Fresnel formulae, showing a profound influence of the gradient and curvature of dielectric susceptibility profiles on the reflectance/transmittance of periodic photonic heterostructures, are presented. Depending on the cutoff frequency of the barrier, governed by the technologically managed spatial profile of its refractive index, propagation or tunneling of light through it is examined. Non-attenuative transfer of electromagnetic energy by evanescent waves, tunneling through dielectric gradient barriers characterized by real values of the refractive index decreasing into the interior of the medium, is shown. Scaling of the results obtained for different spectral ranges of visible, IR and THz waves is illustrated. The potential of gradient optical structures for the design of miniaturized filters, polarizers and frequency–selective interfaces of subwavelength thickness is considere

Nonlinear broadband doubling of the extraordinary wave frequency in inhomogeneous magnetoactive plasma

The nonlinear resonance doubling of radio wave frequencies in inhomogeneous plasma is studied as applied to the ionosphere under the conditions of the phase synchronism between an extraordinary pump wave and its second harmonic. The synchronism is not related to plasma resonances, but is determined by the magnetic field and plasma electron density in the transparency region. The generation efficiency of the second harmonic of a transversely propagating wave is calculated for a wide frequency band lying higher than the lower hybrid resonance frequency. It is shown that this effect is physically analogous to the generation of the second harmonic of laser radiation in a nonlinear crystal. The generation efficiency of the second harmonic is determined for inhomogeneous ionospheric plasma in which the synchronism condition is satisfied in a limited frequency range. It is shown that this effect can be used for remote nonlinear diagnostics of the upper ionospheric plasma, in which the characteristic size of the synchronism region can reach several kilometers. It is proposed to use a combination of satellite and ground-based ion probes in experiments on transionospheric probing. Even if the frequency of the wave emitted from the satellite is lower than the critical frequency in the ionosphere, the frequency of its second harmonic can exceed the critical frequency, so that it can be recorded by a ground-based ion probe or a specially designed receiver. The reflected second-harmonic signal can also be detected at the satellite by using a broadband radio-frequency spectrometer. © 2014 Pleiades Publishing, Ltd

Exactly solvable model for transmission line with artificial dispersion

The problem of the emergence of wave dispersion due to the heterogeneity of a transmission line is considered. An exactly solvable model helps us to better understand the physical process of a signal passing through a non-uniform section of the line and to compare the exact solution and solutions obtained using various approximate methods. Based on the transition to new variables, the developed approach made it possible to construct exact analytical solutions of telegraph equations with a continuous distribution of parameters, which depend on the coordinates. The flexibility of the discussed model is due to the presence of a number of free parameters, including two geometric factors characterizing the lengths of inhomogeneities in values of the inductance L and of the capacitance C. In the new variables, the spatiotemporal structure of the solutions is described using sine waves and elementary functions, and the dispersion is determined by the formulas of the waveguide type. The dispersive waveguide-like structure is characterized by the refractive index N and the cutoff frequency ω. The exact expressions for the complex reflection and transmission coefficients are derived. These expressions describe phase shifts for reflected and transmitted waves. The following interesting cases are analyzed: the passage of waves without phase change, the reflectionless passage of waves, and the passage of signals through a sequence of non-uniform sections. The developed mathematical formalism can be useful for the analysis of a wider range of problems. © 2020 Author(s)

РЕЗОНАНСНОЕ ВОЗБУЖДЕНИЕ И СТРУКТУРА ЭЛЕКТРОМАГНИТНЫХ ПОЛЕЙ В БЛИЖНЕЙ ЗОНЕ ДИЭЛЕКТРИЧЕСКИХ РАССЕИВАТЕЛЕЙ

Theoretical calculations for the appearance of low-frequency resonances excited by linearly polarized electromagnetic waves during a sliding incidence in a rectangular completely dielectric frame are performed. It is shown that the displacement currents generated by these waves in the system lead to the formation of a magnetic dipole, possessed by its own resonant frequency, which is distinctive for the quasistationary fields in the near zone of the scattering frame. The fi elds generated by this are calculated.Выполнены теоретические расчёты возникновения низкочастотных резонансов в прямоугольных полностью диэлектрических рамках, возбуждаемых линейно поляризованными электромагнитными волнами при скользящем падении. Показа но, что токи смещения, генерируемые этими волнами в системе, приводят к об разованию магнитного диполя, обладающего собственной резонансной частотой, характерной для квазистационарных полей в ближней зоне рассеивающей рамки. Рассчитаны возникающие при этом электрические и магнитные поля

Dynamics of electrons in gradient nanostructures (exactly solvable model)

03.65.Ge Solutions of wave equations: bound states, 42.25.Bs Wave propagation, transmission and absorption, 73.63.-b Electronic transport in nanoscale materials and structures,