Biomedical Engineering Reference
In-Depth Information
Figure 6.7
Period of the plasmon helix on a Ag or Au nanowire, embedded
in air (lines) or oil (open circles). The calculations correspond to a vacuum
wavelength
λ
0
=
532 nm (black) or 632.8 nm (red).
in oil. Comparing Ag and Au wires, the helix period is longer on Ag
wires under the same circumstance.
Sofar,wehavediscussedthechiralSPPsinvolvinglow-orderSPP
modes while all the higher order (
m
≥
2) modes are neglected.
Generally, the superposition of different SPP modes of arbitrary
order can generate beating or more complex patterns. If only two
modes are involved, the period of the resulting beating pattern is
given by
π
Re
k
m
,
−
k
m
,
−
1
,where
m
m
. Figure
6.8 shows the beating period as a function of the nanowire radius
at a vacuum wavelength of 632.8 nm. Apparently, the periods
of the plasmon beating grow monotonously as the radius of the
nanowire increases. Further, due to the big difference between the
propagation constants of the
m
=
0and
m
=
3modes,
03
has
the smallest value while
01
is the largest for a given nanowire
radius.
mm
=
2
<
6.5 Applications of Chiral Surface Plasmon Polaritons
AsoriginallyproposedinRef.[19],chiralSPPsonmetallicnanowires
can be used to generate localized chiral near field for enantiomeric
