Article

Geometrical Mie theory for resonances in nanoparticles of any shape

SUPA, Department of Physics, University of Strathclyde, Glasgow, G4 0NG, UK.
Optics Express (Impact Factor: 3.53). 10/2011; 19(22):21432-44. DOI: 10.1364/OE.19.021432
Source: PubMed

ABSTRACT We give a geometrical theory of resonances in Maxwell's equations that generalizes the Mie formulae for spheres to all scattering channels of any dielectric or metallic particle without sharp edges. We show that the electromagnetic response of a particle is given by a set of modes of internal and scattered fields that are coupled pairwise on the surface of the particle and reveal that resonances in nanoparticles and excess noise in macroscopic cavities have the same origin. We give examples of two types of optical resonances: those in which a single pair of internal and scattered modes become strongly aligned in the sense defined in this paper, and those resulting from constructive interference of many pairs of weakly aligned modes, an effect relevant for sensing. This approach calculates resonances for every significant mode of particles, demonstrating that modes can be either bright or dark depending on the incident field. Using this extra mode information we then outline how excitation can be optimized. Finally, we apply this theory to gold particles with shapes often used in experiments, demonstrating effects including a Fano-like resonance.

1 Follower
 · 
127 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: We show that modulation of an optical field injected into a cavity containing a dilute Bose-Einstein condensate is transformed into a modulation of the population of the atomic momentum states due to pseudoresonances of the resolvent which describes the linearized evolution of the atom-cavity system. This effect is related to the way the atomic momentum states and the cavity optical field are dynamically coupled. The results presented offer new possibilities for rapid modulation of atomic momentum state populations up to 3 orders of magnitude faster than modulation of magnetic trapping potentials.
    Physical Review Letters 03/2012; 108(11):113902. DOI:10.1103/PhysRevLett.108.113902 · 7.73 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We report a new approach for accurate calculation of optical cross sections and internal and scattered fields at any point in space for micro- and nanoparticles. Our approach is based on constructing the intrinsic optical modes of general smooth particles and hence optimised surface Green functions that, for any incident field, provide an a priori upper bound on the error and identify the class of incident fields with largest error.
    Journal of Physics Conference Series 05/2012; 367(1). DOI:10.1088/1742-6596/367/1/012010
  • [Show abstract] [Hide abstract]
    ABSTRACT: We study the electromagnetic response of smooth gold nanoparticles with shapes varying from a single sphere to two ellipsoids joined smoothly at their vertices. We show that the plasmonic resonance visible in the extinction and absorption cross sections shifts to longer wavelengths and eventually disappears as the mid-plane waist of the composite particle becomes narrower. This process corresponds to an increase of the numbers of internal and scattering modes that are mainly confined to the surface and coupled to the incident field. These modes strongly affect the near field, and therefore are of great importance in surface spectroscopy, but are almost undetectable in the far field.
    Measurement Science and Technology 06/2012; 23(8):084002. DOI:10.1088/0957-0233/23/8/084002 · 1.35 Impact Factor