Biomedical Engineering Reference
In-Depth Information
Fig. 8.24
(
a
) Halophores (hairs) on the first antenna of seed-shrimp
A. lowryi
(ostracod). (
b
)SEM
image of a diffraction grating on a halophore. Scale bar: (
b
)2
m (Reproduced from [
4
])
Fig. 8.25
(
a
)Flower
H. trionum
.(
b
) Top-view SEM image of the petal of the flower
H. trionum
.
The left-half image corresponds to white epidermis with smooth cells, and the right-half image to
dark epidermis (pigmented) with microscopic striations marked on the cell surface. (
c
) Transverse
cross-sectional SEM image of the dark epidermis of the flower
T. kolpakowskiana
. The period of
the microscopic striations is about 1.2
m (Reproduced from [
111
])
grating. These diffraction gratings can diffract light predominantly in UV, which is
of great significance for attracting pollinators such as bees and birds.
Another grating structure in plants was found in the edelweiss
Leontopodium
nivale
[
113
]. The whole plane including stems, leaves, and bracts is covered
with white hairs consisting of transparent hollow filaments. On the surface of the
filaments there exists an array of parallel ridges with a period of about 420 nm. The
ridges are about 410 nm in height. This curved diffraction grating can block UV light
to reach the cellular tissues underneath since UV light can be strongly absorbed by
the filaments, owing to the interplay of diffraction caused by the grating and guiding
by the ridges.
Structural coloration produced by diffraction gratings requires that the grating
period is comparable to light wavelengths. For wavelengths much larger than the
grating period, only zero-order diffraction (specular reflection) exists. These sub-
wavelength diffraction gratings can be used as antireflective structures. For example,
