Poster Session and Reception

Tuesday, April 25, 2017 - 4:30pm - 6:00pm
Lind 400
  • MITHRA 1.0: A Full-wave Simulation Tool for Free Electron Lasers
    Arya Fallahi (Detsche Elektronen Synchrotron (DESY))
    Free Electron Lasers (FELs) are a solution for providing intense, coherent and bright radiation in the hard X-ray regime. The highly sophisticated dynamics involved in a FEL process was the main obstacle hindering the development of general simulation tools for this problem. We present a numerical algorithm based on finite difference time domain/Particle in cell (FDTD/PIC) in a Lorentz boosted coordinate system which is able to fulfill a full-wave simulation of a FEL process. The developed software offers a suitable tool for the analysis of FEL interactions without considering any of the usual approximations. A coordinate transformation to bunch rest frame makes the very different length scales of bunch size, optical wavelengths and the undulator period transform to values with the same order. Consequently, FDTD/PIC simulations in conjunction with efficient parallelization techniques make the full-wave simulation feasible using the available computational resources.
  • High-order Convergent and Accurate Electromagnetic Solvers for Lipschitz Domains
    Johan Helsing (Lund University)
    We present an integral equation based numerical solver with an extraordinary ability to solve electromagnetic problems in domains with corners, sharp edges, and conical tips. The solver is free from tailor-made special basis functions and precomputed quadratures. Rather, it relies on standard Nyström discretization with underlying adaptive panel-based Gauss--Legendre quadrature. In tandem with that, recursively compressed inverse preconditioning (RCIP) acts as a fast direct solver in regions with troublesome geometry. Thanks to this acceleration, problems in Lipschitz domains can be solved essentially with the same speed and accuracy as problems in smooth domains. Examples include high-wavenumber eigenproblems for axially symmetricmicrowave cavities with piecewise smooth and perfectly conducting (PEC) surfaces; whispering gallery modes (WGMs) and general resonances of dielectric objects in vacuum; and the spectral measure of the polarizability tensor of rectangles, rectangular cuboids, and snow-cone shaped inclusions.
  • General Refraction Problems with Phase Discontinuity
    Luca Pallucchini (Temple University)
    This poster presents the results of the preprint in collaboration with Cristian E. Gutiérrez and Eric Stachura. It provides a mathematical approach to study metasurfaces in non flat geometries. Analytical conditions between the curvature of the surface and the set of refracted directions are introduced to guarantee the existence of phase discontinuities. The approach contains both the near and far field cases. A starting point is the formulation of a vector Snell law in presence of abrupt discontinuities on the interfaces.
  • Dipole Excitation of Surface Plasmons on a Conducting Sheet: Finite Element Simulation and Validation
    Matthias Maier (University of Minnesota, Twin Cities)
    The electric conductivity of atomically thick materials such as graphene and black phosphorous yields an effective complex permittivity with a negative real part in the infrared spectrum. This feature allows for the propagation of slowly decaying electromagnetic waves, called surface plasmons-polaritons (SPPs), that are confined near the material interface with wavelengths much shorter than the wavelength of the free-space radiation.

    The poster summarizes a couple of numerical simulations for a sheet with constant isotropic conductivity embedded in two spatial dimensions; and presents a comparison of the numerical results against the closed-form exact solution based on the Fourier transform. Distinct numerical aspects of the numerical treatment such as local refinement and a-posteriori error control are briefly discussed.
  • Novel Metamaterial Surfaces from Perfectly Conducting Subwavelength Corrugations
    Anthony Polizzi (Louisiana State University)
    We apply an asymptotic analysis to show that corrugated waveguides can be approximated by smooth sylindrical waveguides with an effective metamaterial surface impedance. We show that this approximation is in force when the period of the corrugations are subwavelength. Here the metamaterial delivers an effective anisotropic surface impedance and imparts novel dispersive effects on signals traveling inside the waveguide. These properties arise from the subwavelength resonances inside the corrugations. For sufficiently deep corrugations, the metamaterial waveguide predicts backward wave propagation. In this way, we may understand backwards wave propagation as a multi-scale phenomenon resulting from local resonances inside subwavelength geometry. Our approach is well suited to numerical computation, and we provide a systematic investigation of the effect of corrugation geometry on wave dispersion, group velocity, and power flow.