Biomedical Engineering Reference
In-Depth Information
the typical optical resonance centered at
λ
P
as for their circular
or elliptical cousins [45, 56, 57, 60].
Chiral optical properties of the two enantiomorphic structures
were studied performing a polarization tomography of the light
transmitted through the hole. The method described in Ref. [48,
60] is based on the experimental determination of the 4
4
Mueller matrix [62, 63]. Such a Mueller matrix
M
characterizes the
polarization transformation applied on the incident light beam with
Stokes vector
×
⎛
⎝
⎞
⎠
S
i
0
S
i
1
S
i
2
S
i
3
S
in
=
.
(2.62)
The resultant Stokes vector
S
out
=
M
S
in
is linked to the electric
field
E
[
E
x
,
E
y
] transmitted through the hole. Furthermore,
subsequent theoretical analysis demonstrates a precise connection
betweenthe2
=
×
2Jonesmatrix
J
characterizingthesystemandthe
×
4
4 Mueller matrix
M
[62]. We used an homemade microscope
to focus and control the state of polarization (SOP) of light going
through the chiral structures. In order to study experimentally
the SOP conversion by our structure, we carried out a complete
polarization tomography using the optical setup sketched in Fig. 2.3
(a). A laser beam at
λ
=
780 nm is focused normally onto the
structure by using an objectiveL1. The transmitted light is collected
by a second objective L2 forming an Airy spot on the camera as
expected, as the hole behaves like a point source in an opaque gold
film. In our experiments, the intensity is thus defined by taking the
maximum of the Airy spot [48, 60]. The SOP of light is prepared and
analyzed with half-wave plates, quarter wave plates, and polarizers
located before andafter the objectives.
To illustrate the polarization conversion induced by the chiral
object on the transmitted light, we analyze on Fig. 2.3 (c) the
transformation acting on a linearly polarized input light analyzed
after transmission in four orthogonal SOP Stokes vectors along
the directions:
|
x
(green),
|
y
(yellow),
|+
45
◦
(cyan),
|−
45
◦
(magenta),
(blue). The total transmitted intensity
is also shown (black). The symmetries between both panels
|
L
(red), and
|
R
