Biomedical Engineering Reference
In-Depth Information
2.000
1.031
0.5318
800
0.2742
0.1414
0.07293
700
0.03761
0.01939
0.01000
600
500
400
-40
-20
0
Detector Angle (Degrees)
20
40
FIGURE 25.14
(See.color.insert.).Angle-dependent.transmission.data.for.a.single.valve.of.a.
C. wailesii
diatom.using.the.equip-
ment.shown.in.Fgure.25.2..The.black.lines.superimposed.on.this.image.correspond.to.the.theoretical.zero-.and.
irst-order.diffraction.lines.for.the.2.μm.periodic.structure.within.the.valve..Intensity.in.arbitrary.units.
distribution. proiles. were. digitized. and. used,. in. conjunction. with. single-wavelength.
angle-scan.data.from.the.same.samples,.to.calculate.the.absolute.proportion.of.power.in.
any.portion.of.relected.or.transmitted.solid.angle.
Intense. diffracted. orders. with. sixfold. symmetry. were. observed. when. laser. light. was.
transmitted. through. the. valve. shell. plates. (Figure 25.15d).. Signiicantly. less. intense,. but.
spatially.analogous,.diffraction.was.observed.in.relection..The.spatial.distribution.of.this.
diffraction. pattern. is. entirely. predictable. from. the. sixfold. symmetry. of. the. variation. in.
refractive. index. of. the. valve. ultrastructure.. This. is. conirmed. by. 2D. fast. Fourier. trans-
forms.(FFTs).of.the.periodic.ultrastructure.of.the.internal.surface.geometry.of.the.diatom,.
which.yield.the.same.sixfold.momentum-space.geometries.as.the.diffraction.patterns.(see.
Figure.25.16).[54]..Measurements.of.angular.separation.of.observed.diffracted.orders.for.
each.laser.(e.g..14.1°.(±0.5).for.the.1st.diffracted.orders.using.472.nm).further.conirmed.that.
the.2.μm.periodicity.was.the.source.of.the.observed.diffraction.
(a)
(b)
(c)
(d)
FIGURE 25.15
SEM. images. of. a. diatom,.
C. wailesii
.. (a). A. complete. frustule..(b). High-magniication.image. of. the. inner.wall,.
through.the.apertures.of.which.it.is.possible.to.see.the.outer.plate..(c).Fast.Fourier.transform.of.the.structure.
observed.within.a.
C. wailesii
.frustule..(d).Diffraction.pattern.of.472.nm.of.light.diffracted.by.a.single.
C. wailesii
valve..Scale.bars:.100.μm.(a),.2.μm.(b).
