Biomedical Engineering Reference
In-Depth Information
between the incident field and the active CNP is also echoed in the
dramatic increase in the scattering cross-section shown in Fig. 14.1.
Iftheparticledidnotlocalizeandcaptureasignificantportionofthe
incident field, it would not have the opportunity to produce a large
scattering response. One sees in Fig. 14.2b that above threshold, the
flux of the outward flowing scattered field power generated from
the induced sources in the gain region is large enough to overcome
thelosses.Infact, thestrong expulsionofthepowergenerated from
within the CNP core and resonantly enhanced by the CNP structure
appearstohavepushedtheincidentfieldpowerawayfromtheCNP.
Thismeansthatthescatteredfieldhasbecomelargeenoughthatthe
interaction-basedpowerflowisnowdominatingtheincidentpower
flow in the region around the CNP. As a result, one also observes
the formation of optical vortices on the source side of the CNP
and additional vector field zeros in its neighborhood, as the higher
order modes associated with the scattered field become noticeably
largerinthenearfield.Moreover,thesevorticesappeartobehelping
channel theincident power toward the center of the CNP.
The behavior of the composite normalized Poynting vector field:
S
inc
+
S
ext
, near the active CNP further highlights the behaviors of
thecombinedincidentandinteraction-basedpowerflows.Zoomed-
in views of Fig. 14.2a and 14.2b are given, respectively, in Fig. 14.3a
and 14.3b. The dominance of the resonant dipole fields is clearly
50
45
40
35
30
25
20
15
Figure 14.3
Zoomed-in view of the electric field distributions and the
Poynting vector fields shown in Fig. 14.2 [17].
