Polarization induced by a terahertz electric field on a conductive particle.

摘要

Interactions of an electromagnetic wave with an object of dimensions small compared to the wavelength can often be accounted for by considering the dipole moments, which are effective in explaining the scattering characteristics in the frequency range referred to as the Rayleigh region. Dielectric functions derived from polarization processes due to molecular orientation or bound charge displacements have been employed over the years to account for the scattering properties of particles. In the presence of mobile charges, bulk conductivity may be incorporated with a complex dielectric function to explain the peak in absorption near the plasma frequency exhibited by metallic particles in the optical region. With the current interest in nanostructures, an investigation of the electromagnetic properties of a conductive particle with attention given to space-charge effects would appear timely. This can be accomplished by coupling the transport equations of the charge carriers to the Maxwell's equations. Results of computations performed for elementary structures such as plates and particles revealed the screening of the internal field while dispersion and absorptions effects are shown by the complex dipole moments. To gain insight into the nature of charge-wave interactions, results based on quasi-static formulation for the electric field will be compared with those based on full-wave analysis, with special attention given to the charge and current distributions within the structure. By consideration of the physical process of charge carrier motion and lattice polarization, the equivalent circuit model for a conductive nanoparticle in the terahertz frequency range is developed. All circuit elements are of electrical nature and can be directly expressed in terms of material parameters. The equivalent circuit can serve as the basis of analysis for composite structures and aggregates of which the conductive nanoparticle is a constituent.