Biomedical Engineering Reference
In-Depth Information
(a)
Bead image before
correction
14,560
10,920
7,280
3,640
0
Bead sub-images before
correction
Bead sub-images after
correction
3
×
3 phase ramps for
offset of sub-images
(c)
(b)
3
×
3 ramps plus beam
deflection correction
6
4
2
0
-
2
-
4
-
6
6
4
2
0
-
2
-
4
-
6
(d)
Corrective wavefront,
composite approach with
phase reconstruction
(e)
Corrective wavefront,
independent approach
with measured phase
Bead image after
composite correction
Bead image after
independent correction
1.5
1
1
0.5
0.5
0
0
FIGuRE 13.17
AO.correction.for.system.aberration.using.only.a.single.image..(a).Image.of.a.1.μm.bead.without.
system.aberration.correction..(b).Ater.simultaneously.applying.diferent.phase.gradients.to.each.of.the.3.×.3.subre-
gions.of.the.SLM,.nine.spatially.ofset.images.of.the.same.bead.were.seen..he.deviations.from.the.ideal.3.×.3.array.
indicate.the.aberration-induced.tilt.error.in.each.subregion..(c).Correcting.these.tilt.errors.causes.the.bead.subim-
ages.to.become.aligned.with.the.ideal.3.×.3.array..(d).he.corrective.wavefront.obtained.using.the.tilt.error.data.and.
phase.reconstruction,.and.the.resulting.corrected.bead.image,.both.of.which.were.similar.to.those.obtained.by.3.× 3.
independent.masks.and.direct.phase.measurement.(e)..Scale.bar:.2.μm.
imaging.methods.more.than.difraction-limited.imaging.methods..For.example,.a.two-photon.luores-
cence.image.could.still.be.obtained.under.the.same.system.aberration.shown.in.
Figure.13.18
,.while.a.
STED.microscope.would.operate.poorly.
13.5.6 Zonal-Based Approaches for Scattering control
In. this. chapter,. we. described. how. segmenting. the. pupil. into. diferent. zones. allows. us. to. achieve. AO.
correction.for.images.degraded.by.refractive.index.variations.in.the.sample..In.other.words,.in.strongly.
scattering.samples.such.as.brains,.AO.corrects.the.light.weakly.delected.from.refractive.bodies.of.multi-
wavelength.scale,.but.not.the.light.multiply.scattered.by.sub-wavelength.particles,.for.which.much.iner.
correction.patterns.are.required..In.recent.years,.zonal.wavefront.shaping.has.also.been.used.to.con-
trol.multiply-scattered.light.to.achieve.focusing.through.turbid.media.[19].and.has.been.demonstrated.
recently.to.form.difraction-limited.luorescence.images.through.samples.that.are.16.mean-free.scatter-
ing.lengths.in.thickness.[20]..he.experimental.approaches.in.these.methods.are.zonal,.like.ours—the.
wavefront.is.segmented.into.hundreds.or.thousands.of.zones,.and.the.phase.in.each.zone.is.varied.while.
monitoring. the. resulting. signal. change.. Unlike. ours,. they. are. iterative—many. passes. are. required. to.
