Biomedical Engineering Reference
In-Depth Information
of two terms [34]:
Q
abs
=
Q
abs,
ε
+
Q
abs,
ξ
Im(
ε
)
E
ω
·
E
ω
2
π
=
ω
dV
V
0
Re
2
dV
B
ω
·
E
ω
−
E
ω
·
B
ω
+
ω
π
V
0
Im(
ξ
)Im
dV
2
π
Im(
ε
)
E
ω
·
E
ω
dV
−
ω
π
E
ω
·
B
ω
=
V
0
V
0
(1.23)
The physical meaning of this equation is that absorption occurs due
to both properties of the system—the dissipative property (
Q
abs,
ε
)
and the chiral property (
Q
abs,
ξ
). The first term of Eq. (1.23) comes
from a dielectric function of an NC or a molecular medium and the
secondtermresultsfromtheso-calledopticalchiralitythatinteracts
with a chiral medium. We find the second term is linear in the
chiral parameter
ξ
c
. It is indeed proportional to the optical chirality
parameter
C
(
r
), if we compare it with Eq. (1.21) that has been
derived from the Maxwell'sequations (1.4).
The absorption CD signal will be the difference in Eq. (1.23) for
the incident beams ofLCP and RCP:
CD
abs
=
CD
abs,
ε
+
CD
abs,
ξ
. (1.24)
Then, the CD contribution from the chiral properties of a molecular
medium in Eq. (1.24) can be expressed as:
CD
abs,
ξ
=−
ω
π
ξ
c
)Im
dV
E
ω
+
·
B
ω
+
Im(
V
0
Im(
ξ
c
)Im
dV
+
ω
π
E
ω
−
·
B
ω
−
V
0
∝
Im(
ξ
c
)(
C
+
(
r
)
−
C
−
(
r
))
dV
(1.25)
V
0
where the signs
+
/
−
indicate that the incident beam is LCP or RCP.
For several specific core/shell metal-molecular structures, explicit
analytic expressions and as well numerical results for both
CD
abs,
ε
and
CD
abs,
ξ
can be found in Ref. [34].
When we look closely at (1.23), we should note that the elec-
tromagnetic fields
E
and
B
are the self-consistent electromagnetic
