Near-field optical properties of silver nanocylinders arranged in a Pascal triangle

PLASMONIC PROPERTIES OF DIELECTRIC-CORE PLASMONIC-SHELL NANOCYLINDERS IN PASCAL TRIANGLE

We report on the plasmonic properties of silver-coated dielectric nanocylinders arranged according to an unconventional geometrical representation called Pascal's triangle. We performed numerical simulations to calculate the extinction spectrum and identify the collective optical modes in the geometry. For resonant excitation at 410 nm, we found pronounced field localization (50 nm) at the center of the Pascal triangle. Further, we studied the near-field intensity as a function of experimentally-relevant variables such as excitation wavelength, angle of incidence and dielectric constant of the core material. Our analysis revealed pronounced difference between near-field intensities for resonant and non-resonant excitation wavelength at various angle of incident radiation; and an increment in near-field intensity at excitation wavelengths greater than 600 nm, with increase in dielectric constant of core material. Our study has relevance in development of substrates with tunable electromagnetic hot-spots for on-chip plasmonics.

Surface plasmon near-field resonance characteristics of silver shell nanocylinders arranged in triangular geometry

The optical near-field surface plasmon effects of a triangular system of silver nanoshell cylinders are numerically studied using the two-dimensional finite difference time domain method. The dependence of interparticle distance, shell thickness of the cylinder, dielectric constant of shell core as well as embedding medium, and orientation of the optical source plane on the plasmonic resonances of the nanocylinder shells is studied. The plasmonic resonances are found to have strong dependence on the interparticle distance. As the size of the particle is increased, the field intensity peak shows a redshift. The resonance condition varies with the dielectric constant of the environment as well as the core. In addition, the orientation of the incident source plane has a significant role in the near-field intensity distribution. Since the near-field intensity has the same trend as that of the scattering cross section, the results can be used in the design of various applications like sensing, antennas, and waveguides.

Superfocusing effect in the chain of silver nanorods

A chain of three silver nanorods with progressively decreasing sizes and separations is designed to focus the electric fields around the small nanorods. The optical properties of the chain of silver nanorods are investigated by the discrete dipole approximation method. The results show that, compared with the individual small nanorod and the chain of two nanorods, many enhanced electric fields are focused around the small nanorod of the chain of three nanorods due to the electric field couplings between adjacent nanorods. Therefore, the design of the chain of three nanorods provides a way to obtain stronger electric fields. In addition, how the structural parameters of the chain of three nanorods affect their optical properties is also studied.