Biomedical Engineering Reference
In-Depth Information
(a)
(b)
(c)
(d)
FIGURE 25.9
Picture. of. a. fractured. scale. from.
E. schoenherri pettiti
,. with. closeup. images. of. the. differently. colored. regions.
within.the.scale.showing.that.the.differences.between.the.colors.observed.are.not.the.periodicity.of.the.crystal..
(a).A.single.predominantly.yellow.scale.from.the.light.green.region.of.
E. schoenherri pettiti
..Subsequent.images.
are.higher-magniication.pictures.of.the.colored.regions.seen.in.the.picture..(a,.b).Yellow.region.with.a.mea-
sured.periodicity.of.283.nm..(c).Green.area.with.a.periodicity.measured.to.be.288.nm..(d).Blue.region.with.a.
periodicity.of.330.nm..Scale.bars:.20.μm.(a),.3.μm.(b-d).
While. this. qualitative. observation. does. lead. to. the. conclusion. that. similarly. periodic.
domains.can.result.in.different.colors,.it.does.not.explain.how.this.arises. or.what.other.
factors.lead.to.changes.in.the.observed.color..In.order.to.examine.this,.singles.scales.were.
mounted.onto.the.head.of.a.ine.needle.and.examined.using.a.dark.ield.microscope.(Nikon.
TE2000-U).attached.to.a.spectrometer.(Acton.SpectraPro.2500i),.which.allowed.the.relec-
tion.from.a.single.domain.to.be.observed.and.measured.concurrently.(Figure.25.10).
A.single.scale.from.
E. magniicus
,.mounted.on.a.pin,.was.placed.at.the.focal.point.of.the.
microscope.. Although. this. illuminates. the. entirety. of. the. scale. as. well. as. the. pin. upon.
which.the.scale.is.mounted,.the.spectrometer.can.be.conigured.to.calculate.the.spectrum.
from.a.limited.area.of.the.internal.imaging.plate,.thereby.measuring.the.relected.spec-
tra.from.individual.sections.of.individual.domains.while.the.scale.is.rotated.azimuthally.
around.the.axis.of.the.pin.in.small.increments.
The. most. noticeable. feature. of. these. results. is. that. while. the. intensity. of. the. relected.
light.changes,.the.color.of.the.observed.relection.does.not.change.signiicantly.with.small.
changes.in.angle..This.appears.to.demonstrate.that.in.this.optical.geometry.the.photonic.
crystal.within.the.weevil.scale.interacts.with.the.incident.light.with.the.same.optical.char-
acteristics.over.a.range.of.angles..As.a.feature,.this.allows.for.the.relection.from.the.surface.
of.the.scale.to.be.enhanced.over.the.relection.by.a.pigment.by.the.presence.of.the.photonic.
crystal.while.allowing.the.striking.color.to.be.evident.over.a.wider.range.of.angles.
