Using the plasmon hybridization method, we investigate the optical properties of metallic tori of different shapes and for different polarizations. The plasmon energies are found to be strongly dependent on polarization and on the aspect ratio of the torus, which we define as the ratio of the radii of the two circles that define the structure. For incident light polarized in the plane of the torus, the optical spectrum is characterized by two features, a long wavelength highly tunable dipolar plasmon resonance, and a short wavelength mode corresponding to excitation of several higher order torus modes. For aspect ratios smaller than 0.8, we find that the energy of the tunable dipolar torus mode can be described analytically as an infinite cylinder plasmon of a wavelength equal to the length of the tube. For perpendicular polarization, the spectrum exhibits a single feature made up of several closely spaced higher order torus modes which are only weakly dependent on the aspect ratio. The calculated optical properties are found to be in excellent agreement with results from numerical finite difference time domain calculations and with results from other groups.
Measurements and calculations of differential cross sections for direct scattering, single charge transfer, and double charge transfer in collisions of 1.5-, 2.0-, 6.0-, and 10.0-keV 'He + with a He target
The formulation of the van der %aals (VDW) interaction between atoms in terms of frequencydependent polarizabilities is extended to the problem of the long-range contribution to thehyperfine pressure shift in optical-pumping experiments. The requisite perturbed-energy expression for the present problem involves two orders of VDW interaction and one order of magnetic hyperfine interaction. This expression is recast in terms of integrals involving requisite frequency-dependent response functions which are evaluated using the Brueckner-Goldstone many-body technique applied earlier to VDW energy calculations. Specific applications are made to H-He and H-Ne systems. The fractional shift 6@/@0of the hyperfine constant is expressed in the form of DHX/B6, where R (a.u. ) is the separation between H and X atoms.The values we obtain for DHx are 13. 34 and 26.13 for X= He and Ne, respectively. This analysis removes one of theimportantuncertainties in hyperfine-pressure-shift calculations, namely, the influence of coxrelation effects on the long-range part of 6 8/80.
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