Biomedical Engineering Reference
In-Depth Information
Figure 15.24
(a) Relative transmission of the sample as a function of fre-
quency, defined as the ratio of the transmitted spectrum for light polarized
paralleltothelongaxisofthenanoantennasoverthetransmittedspectrum
for perpendicular light polarization. (b) Comparison between experimental
andnumericallycalculatedextinctione
cienciesasafunctionoffrequency.
Figures (a) and (b) reproduced from Ref. 83, with permission of the Optical
Society of America.
From T
rel
, we can then estimate the nanoantenna extinction
e
ciency Q
ext
as:
σ
ext
σ
geo
=
A(1-T
rel
)
NLD
Q
ext
=
(15.3)
where
σ
ext
is the nanoantenna extinction cross section,
σ
geo
=
LD
the geometric cross section,
A
the illuminated area, while N, L, and
Darethenumber,lengthandwidthoftheilluminatednanoantennas,
respectively.
In Fig. 15.24b experimental “Q
ext
” (black trace) shows a clear
peak at 1.4 THz, in correspondence to the extinction peak of the
relatedtransmittancespectrum,withamaximume
ciencyofmore
than 100.
To better understand the resonance characteristics of terahertz
nanoantennas array we performed numerical simulations. The
nanoantenna design resembles the fabricated structure and all
the simulations parameters are the same as the ones used in
[83]. The calculated extinction e
ciency, in good agreement with
experimental values, is represented in Fig. 15.24b (green trace).
Simulations also provide near field properties of the nanoan-
tenna. Figure 15.25a depicts the electric field norm around the
