Leonid A. Melnikov

Perfect absorption in graphene multilayers

We demonstrate that 100% light absorption can be achieved in a graphene-based hyperbolic metamaterial, consisting of periodically arranged graphene layers which are tilted with respect to the interface. The geometrical parameters of the multilayered structure and the chemical potential of graphene are chosen in such a way that the in-plane relative effective permittivity is close to 1. Under this condition, the graphene multilayer exhibits asymmetry which appears as a very large difference between waves propagating upward and downward with respect to multilayer boundaries. One of them has a very high attenuation constant and neither of the waves undergo reflection at slab interfaces, resulting in total absorption even for an optically ultra-thin slab.

Optical vortices in a vector field: the general definition based on the analogy with topological solitons in a 2D ferromagnet, and examples from the polarization transverse patterns in a laser

New approaches to the characterization of the vector vortical structure of the paraxial monochromatic field are introduced using the analogy between vector field singularities in a distribution of the unit vector of normalized Stokes parameters m(X,Y,Z),m2 = 1 in the transverse plane and topological solitons in a 2D ferromagnet. In this approach the vector vortex of the first order appears as zero and pole of the complex homographic function w = (X + iY)(1-Z)-1. The application of the developed method to the results of numerical simulations of a large aperture Zeeman laser is presented.

Multi-soliton fission and quasi-periodicity in a fiber with a periodically modulated core diameter

Abstract A mathematical model will be presented that results in an equation similar to the nonlinear Schrodinger equation containing all common dispersion terms, i.e. material dispersion, waveguide dispersion and profile dispersion. Using this equation numerical solutions are performed for two distinct situations: (i) N -soliton ( N =1, 2, 3) pulse propagation and (ii) two-coupled-soliton pulse propagation. Soliton fission and various modulations of the pulse profile will be discussed.

Super-Planckian far-zone thermal emission from asymmetric hyperbolic metamaterials

We demonstrate the production of strong directive thermal emissions in the far-field zone of asymmetric hyperbolic metamaterials (AHMs), exceeding that predicted by Plancks limit. Asymmetry is inherent to the uniaxial medium, where the optical axis is tilted with respect to medium interfaces. The use of AHMs is shown to enhance the free-space coupling efficiency of thermally radiated waves, resulting in Super-Planckian far-field thermal emission in certain directions. This effect is impossible in usual hyperbolic materials because emission of high density of states (DOS) photons into vacuum with smaller DOS is preserved by the total internal reflection. Different plasmonic metamaterials are proposed for realizing AHM media; the thermal emission from a AHM, based on a grapheme multilayer structure, is presented, as an example.

Calculation of a hydrogen atom photoionization in a strong magnetic field by using the angular oblate spheroidal functions

A new efficient method for calculating the photoionization of a hydrogen atom in a strong magnetic field is developed based on the Kantorovich approach to the parametric boundary problems in spherical coordinates using the orthogonal basis set of angular oblate spheroidal functions. The progress as compared with our previous paper (Dimova M G, Kaschiev M S and Vinitsky S I 2005 J. Phys. B: At. Mol. Opt. Phys. 38 2337–52) consists of the development of the Kantorovich method for calculating the wavefunctions of a continuous spectrum, including the quasi-stationary states imbedded in the continuum. Resonance transmission and total reflection effects for scattering processes of electrons on protons in a homogenous magnetic field are manifested. The photoionization cross sections found for the ground and excited states are in good agreement with the calculations by other authors and demonstrate correct threshold behavior. The estimates using the calculated photoionization cross section show that due to the quasi-stationary states the laser-stimulated recombination may be enhanced by choosing the optimal laser frequency.

Soliton fission management by dispersion oscillating fiber.

We report the experimental observation of the fission of picosecond solitons in a fiber with sine-wave variation of the core diameter along the longitudinal direction of propagation. The experimental pulse dynamics is reproduced by numerical simulations. The fission of high-intensity solitons caused by both the variation of the fiber dispersion and stimulated Raman scattering is demonstrated. The number of output pulses and their frequencies can be managed by periodical modulation of the fiber dispersion even under the strong effect of the Raman scattering.

Generation of Picosecond Pulse Train With Alternate Carrier Frequencies Using Dispersion Oscillating Fiber

The train of picosecond pulse pairs with alternate carrier frequencies was observed when the train of picosecond pulses was launched into the fiber with sine-wave variation of the core diameter. The effect occurs due to dispersion oscillations along the fiber length, which result in splitting high-order solitons. In the experiments, the splitting of second-order soliton was observed. The separation between carrier frequencies of output pulses depends on the phase of periodical oscillation of the fiber dispersion. Numerical simulations were made and show good agreement with the experimental results.

Numerical studies of beam and pulse propagation in lasers and nonlinear media: Transverse pattern dynamics and nonparaxial effects☆

Abstract A review of recent work in numerical modelling of transverse pattern formation and dynamics in lasers and nonparaxial beam propagation is presented. The algorithms developed involve the field decomposition in terms of the Gaussian-Laguerre modes. Three models are discussed in detail. In the first one, the transverse pattern evolution of a short pulse in a ring unidirectional laser with a homogeneously broadened optically thin active medium is considered under the approximation of transversely synchronous pulse. The pulse-train envelope and transverse pattern dynamics are studied numerically using more than 200 empty cavity modes. In the second model the limitation of thin active medium is removed, and the propagation of self-acting beam through the active medium of arbitrary thickness is taken into account solving the conventional paraxial wave equation. Stationary regimes with deformed modes, quasi-periodic oscillations, and mode-locking regimes are observed. Phase singularities (optical vortices) in the transverse field pattern are demonstrated. In the third model, the Gauss-Laguerre decomposition is used to solve the Helmholtz equation describing wide-angle (nonparaxial) beam propagation in nonlinear media. The role of backward waves in wide-angle Kerr self-focusing is discussed.

Plasmonic Coaxial Waveguides with Complex Shapes of Cross-Sections

In this paper, we describe waveguide properties of new optical waveguides made of noble metals and filled with glass and air. Such waveguides are coaxial cables and differ from a conventional coaxial in the shape of their central rods. Coaxial waveguide with annular and elliptic central rods are considered. Numerical simulations demonstrate that these waveguides, having nanosize cross-section, support propagation of few comparatively low-loss modes, having phase velocity close to the speed of light and the fields localized in a small area outside a metal. We illustrate excitation of these coaxial modes by dipole-like sources.

Optimisation of microstructured waveguides in z-cut LiNbO 3 crystals

We present a practical approach to the numerical optimisation of the guiding properties of buried microstructured waveguides, which can be fabricated in a z-cut lithium niobate (LiNbO3) crystal by the method of direct femtosecond laser inscription. We demonstrate the possibility to extend the spectral range of low-loss operation of the waveguide into the mid-infrared region beyond 3um.