ABSTRACT
Scattering of electromagnetic radiation by electrically charged spherical particles is treated theoretically. A generalization of the approach is performed by incorporating both intraband and interband effects, while a new oscillatory term corresponding to the classical dispersion theory and the semi-quantum approach is considered. It is shown through a set of numerical experiments that interband effects may reduce the amplitude of resonant peaks for scattering, Q(sca), and absorption, Q(abs), and cause a shift of peak positions to longer wavelengths. In general, the resonant features due to interband and intraband effects can occur at different frequencies; thus, both together may result in qualitatively and quantitatively new optical signatures of electrically charged particles. This is a motivating factor for experimentalists who can use the particles as targeted probes, for example, in mapping the electric fields in different media based on scattering and/or absorption properties of electrified particulate systems.
ABSTRACT
The mechanism of charge on the near-field intensity distribution is revealed for metallic and dielectric particles with sizes ranging from 10 nm to 10 µm. The theoretical foundation of near-field intensity perturbations is in the discontinuity of the tangential components of the magnetic fields on either side of the interface between the particle and its surrounding medium, since excess electrons form a thin metal-like layer with elevated conductivity. We have shown that the local fields alter marginally if charges are imposed on a surface of a metallic particle. But an intensity amplification is identified in the vicinity of charged dielectric particles with sizes smaller than the wavelength. Specifically, we have demonstrated that the electromagnetic field is amplified near the poles of the particle as a result of the oriented electric and incident fields. In contrast, a dielectric particle that is large compared to the wavelength becomes opaque with a deep shadow at the side opposite to the beam incidence. As a result, intensity damping is identified near a charged sphere in the geometric optics regime. At significant charge densities, the physical properties of a conductive layer play a dominant role in forming the 3D intensity distribution independent of conductivity or permittivity of the particle core. These findings suggest that some electrically chargeable particles have the potential to be used as optical devices with properties tunable through their net surface charge.
ABSTRACT
This Letter treats the scattering of electromagnetic waves by an electrically charged spherical particle in near-field approximation. Particular attention is paid to the external intensity distribution at the outer edges of the particle. The difference between scattering by a charged sphere and an electrically neutral sphere is significant only when size parameters exceed unity.