Biomedical Engineering Reference
In-Depth Information
(a) Ag/SiO
2
configuration
(b) SiO
2
/Au IO configuration
Figure 14.4
The theoretical effective and physical bulkgain coe
cients
in cm
−
1
versus the effective gain parameter
κ
for the Ag/SiO
2
and the
corresponding SiO
2
/Au IOactive CNP designs [17].
advantageousfromafabricationpointofview.Thebulkandeffective
gainvaluesforthisIOdesignareshowninFig.14.4b.Again,itisclear
that the scattering cross-section enhancement factor drastically
reduces the bulk gain value required at resonance. On the contrary,
a comparison of Fig. 14.4a and 14.4b shows that the required gain
for the active CNP design is much less than that for the IO design.
Furthermore, as discussed in [17], one can observe from Fig. 14.4
that the active CNP design would be less sensitive to variations in
the experimental gain parameters.
The active CNP and IO systems are both two-layer designs.
Although their configurations are complementary to one another,
they exhibit similar behaviors. Since the active CNP design has
a much stronger resonance than the one produced by the IO
design, one could argue that adding an exterior metal shell coating
to the IO design would be make it more like an active CNP. As
shown in Fig. 14.5, this three-layer, alternate coated IO design does
perform well and still radiates a dipolar mode. We note that given
the experimentally realized IO particle was designed using OG-
488 dye [39], which has a certain gain linewidth, any real design
would have to have its geometry resonance matched to those lines.
Consequently,onlyathin3.0nmAgshellwasaddedtotheIOdesign.
It only shifts the resonance slightly down to the shorter wavelength
