Biomedical Engineering Reference
In-Depth Information
streamlineshowtheveryelectricallysmallCNPshavecross-sections
much larger than their physical size under plane wave excitations
andhowthisbehaviordecreasestheactualgainconstantsneededto
achieve amplification. Next, we will discuss how their designs vary
when ideal gain material and quantum dots are taken into account.
Comparisonsofresonantconfigurationswiththegainmediumbeing
contained within the dielectric core surrounded by the metallic
shell and its inverse with the gain medium covering a metallic core
(inside-out or IO case) will be presented. We have identified the
formerasbeingthepreferred one.Finally,wewillillustratehowthe
active CNPs act as nano-amplifiers and nano-jammers of quantum
emitters with EHD excitations.
14.2 Coated Nanoparticles Excited by a Plane Wave
Resonant, active CNPs, when properly designed, capture sig-
nificantly more of the incident field energy than its physical
size suggests is possible. The corresponding enhancement of its
extinction cross-section is correlated with the concentration of the
local field energy into its gain region. This energy localization can
be visualized with the behavior of the flow lines of the Poynting
vector field in the neighborhood of the CNP. Strong expulsion of
the optical power generated from the interaction of the captured
incident field energy with the gain medium creates an intense
scattered field. As the interactions between the scattered field
and the exciting plane wave increase, optical vortices form in
the neighborhood of the active CNP. Gain depletion eventually
occurs when the increase in the effective gain su
ciently detunes
the resonance. A simple model for the gain enhancement effects
observed in active CNPs relates the enhanced effective size of the
CNPcausedbythefieldlocalizationtotherequiredgainnecessaryto
achieveitssuper-resonantstate.Acomparisonofthemetal-covered,
gain core, active CNP studied previously to the experimentally
realized gain-impregnated silica-covered metal “spaser” suggests
thattheactiveCNPdesignwouldrequiresignificantlylessgainwhile
offering a much larger enhancement of the incident field. Proposed
modificationsofbothgeometriesthataugmentthefieldlocalization
