Phase diagram for investigating the scattering properties of passive scatterers

Abstract

The study of scattering (i.e., how a single receiver or scatterer responds to an external stimulus) is relevant to a wide range of subjects that are, in some way, related to wave physics (e.g., electromagnetic radiation, elastic waves, thermal diffusion, and quantum physics). Inspired by the recent developments of metamaterials and state-of-the-art nano-optical technologies, the design of functional scatterers has attracted much attention over the last decade (both experimentally and theoretically). For instance, unusual scattering states (including invisible cloaking, resonant scattering, coherent perfect absorption, superscattering, and superabsorbers) have been demonstrated when specific materials are used in the configuration of multilayered structures.1–5 Devices in which these scattering states are used have great potential for applications in biochemistry, greenenergy generation, ultrasensitive detection sensors, and optical microscopy. To obtain the exotic electromagnetic properties at a subwavelength scale, however, a variety of specific conditions need to be satisfied and a better understanding of scattering coefficients is thus required. The study of light radiation being scattered from small particles can be traced back to Lord Rayleigh’s explanation for the color of the sky.6 Furthermore, an exact solution for spherical scatterers was derived by Mie and Lorenz more than a century ago.7 This solution is valid for particles with any geometrical size, and for possible permittivity and permeability values. Nonetheless, although a basic understanding of the recently discovered unusual scattering states can be derived from existing scattering theory, a unified understanding of all these exotic states is still lacking. Figure 1. Phase diagram for a passive scatterer defined by the magnitude, jC .TE;TM/ n j, and the phase, .TE;TM/ n , of the transverse electric (TE) and transverse magnetic (TM) modes of electromagnetic radiation (where n denotes the order of the harmonic channel). The colored region represents the allowable solutions of C .TE;TM/ n and the white region represents the forbidden states for passive scatterers. The value (i.e., color) of the contours represents the normalized absorption cross section ( abs) for the TE or TM modes. : Wavelength of electromagnetic radiation.8