Biomedical Engineering Reference
In-Depth Information
1
4-conjugates
0.8
-Fan-summ
-Tokovinin
0.6
-Parallel-sum
2-conjugates
0.4
-Fan-summ
0.2
-Tokovinin
-Parallel-sum
0
0
0.1
0.2
0.3
0.4
0.5
Field position (mm)
(a)
1
-Inverse-
medium
no refraction
-Inverse-
medium
with refraction
0.8
0.6
0.4
-4 conjugates
-2 conjugates
0.2
-Uncorrected
0
0
0.001
0.002
0.003
0.004
0.005
0.006
Refractive-index di€erences
(b)
FIGuRE 15.11
(a).Correction.across.the.ield.of.view.for.diferent.multiconjugate.adaptive.optics.schemes..he.
sample.consists.of.500.Gaussian.spheres.with.
δ
n
.=.0.003..(b).he.efect.of.refractive-index.diferences.on.diferent.
multiconjugate.adaptive.optics.schemes..he.sample.again.consists.of.500.Gaussian.spheres.with.varying.
δ
n
..he.
irst.data.point.is.at.a.refractive-index.diference.of.0.0001.(Kam.et.al.,.2007).
of simulations.in.which.a.the.sample.is.modeled.by.500.randomly.positioned.Gaussian.luctuations.in.
the.refractive.index.(Kam.et.al..2007)..We.evaluate.the.use.of.two.and.four.adaptive.elements.with.three.
diferent. methods. for. calculating. the. phase. correction. from. each. element.. he. simplest. method. is. the.
“parallel. sum,”. where. the. phase. aberration. accumulated. from. a. inite. slice. within. the. sample. volume.
is.integrated.along.the.optical.axis.and.corrected.by.an.element.positioned.at.a.plane.conjugated.to.the.
middle.of.this.slice..A.more.realistic.method.takes.account.of.the.fact.that.light.rays.forming.the.image.
traverse.the.sample.while.illing.the.whole.NA..he.“fan.sum”.therefore.calculates.the.phase.aberration,.
averaging.over.the.NA.fan.of.rays..he.Tokovinin.method.is.based.on.a.proposal.for.an.optimized.integral.
that.laterally.blurs.the.phase.contribution.of.each.plane.the.farther.it.is.from.the.conjugate.(Tokovinin.
et.al..2000).We.evaluate.the.results.by.calculating.the.Strehl.ratio.for.each.case.across.the.ield.of.view.
(Figure.15.11a).and.on.axis.as.the.refractive.index.diferences.in.the.sample.increase.(Figure.15.11b).
15.3 Wavefront Measurement and correction Approaches
15.3.1 open-Loop correction of Depth Aberration
he.approach.we.follow.is.to.correct.the.depth.aberrations.resulting.from.the.ray.path.length.diferences.
given.by.Equation.15.1.or.15.2..he.shape.of.the.DM.is.then.given.by
