Biomedical Engineering Reference
In-Depth Information
engineered.with.coatings.to.preserve.them.in.diferent.conditions.and.can.be.made.to.target.diferent.bio-
logical.tissues,.organelles,.cell.walls,.or.other.biological.structures.(Invitrogen.Corporation,.2010)..hey.
can.be.introduced.into.the.sample.by.diferent.mechanisms.such.as.negative.pressure.injection,.pressure.
injection,.matrotrophycally,.difusion,.and.others.(Guldband.et.al..2010;.DeMarais,.Oldis,.&.Quatrro.2005;.
Rowning.et.al..1997)..In.particular,.luorescent.microspheres.have.been.injected.previously.in. Drosophila .
embryos.(Kalpin,.Daily,.&.Sullivan.1994)..Suiciently.small.luorescent.microspheres,.as.described.earlier,.
are. difraction-limited. when. imaged. by. the. SHWF. sensor,. enabling. their. use. as. point-source. reference.
beacons.for.the.operation.of.the.SHWF.sensor..Azucena.et.al..(2010).show.that..multiple.beads.can.also.
be.used.to.directly.measure.the.wavefront..he.wavefront.measurements.from.multiple.beads.and.a.single.
bead.difer.only.in.the.higher-order.aberrations.(e.g.,.above.the.seventh.radial.order.Zernike).
17.1.2 Shack-Hartmann Wavefront Sensor
A.SHWF.sensor.samples.the.wavefront.at.diferent.points.of.the.pupil.by.using.a.lenslet.array.to.measure.
the.mean.slope.across.each.subaperture.as.shown.in.Figure.17.1..On.the.one.hand,.Figure.17.1a.shows.a.
lat.wavefront.impinging.onto.the.SHWF.sensor;.as.can.be.seen,.there.is.a.slope.of.zero.measured.at.each.
of.the.Hartmann.spots..Figure.17.1b,.on.the.other.hand,.shows.a.distorted.wavefront.impinging.onto.the.
SHWF.sensor..he.spot.displacement.at.each.subaperture.is.directly.proportional.to.the.product.of.the.
mean.slope.at.the.subaperture.and.the.focal.length.of.the.lenslet..he.wavefront.can.be.reconstructed.
using.Equations.17.2.and.17.3.(Liang.et.al.,.1994):
(
)
w x y
x
,
=
x
i
i
i
.
.
.(17.2)
f
LA
(
)
w x y
y
,
=
y
i
i
i
.
.
.(17.3)
f
LA
Flat wavefront
CCD
Aberrated wavefront
CCD
d s
d s
Lenslet array
(a)
(b)
FIGuRE 17.1 A.Shack-Hartmann.wavefront.sensor.measures.the.mean.slope.at.each.subaperture;.this.information.
is.used.to.reconstruct.the.wavefront.over.the.whole.aperture..(a).Flat.wavefront;.(b).distorted.wavefront.
 
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