Biomedical Engineering Reference
In-Depth Information
Figure 6.2
Excitation of chiral SPPs on a metallic nanowire by a paraxial
Gaussianbeamincidentsnormallyontoonenanowireterminal.Thebeamis
linearly polarized with an angle
to the
x
-axis. The origin of the coordinate
is located at the center of the input end, though it is offset for clarity in the
figure.
θ
It is suggested that the high-order SPPs on cylindrical wire can be
viewed as being propagating spirally over the wire surface [24].
Actually, this interpretation comes from the decomposition of the
wave vector into an axial and an azimuthal component and it is in
principle different from the chiral SPPs discussed here.
Under excitation at the nanowire end, those modes with profiles
overlappingwiththeincidentlightcanbeexcitedsimultaneously.As
shown in Fig. 6.3, for incident polarization parallel to the nanowire
axis, the
m
=
0and
m
=
1(
z
-direction) modes can be excited.
For perpendicular polarization, the
m
=
1(
y
-direction) and
m
=
2 modes are excited. If the radius of the nanowire is small enough
so that higher order modes (
m
≥
2) are cutoff (see Fig. 6.1), we
have the
m
=
0 and two degenerate
m
=
1 modes excited on
the nanowire for oblique polarization. Comparing Fig. 6.3(b) and
Figure 6.3
Optical excitation of different SPP modes for incident polar-
ization parallel (a, b) or perpendicular (c, d) to the wire axis.
φ
denotes
the incident phase of the excitation beam. Reproduced from Ref. [19], with
permission of the American Physical Society
