Biomedical Engineering Reference
In-Depth Information
In.this.chapter,.we.will.discuss.the.speciic.issues.related.with.an.AO.system.in.terms.of.optical.system.
design. considerations,. the. fundamental. imaging. errors. associated. with. optical. systems,. how. to. diag-
nose. the. fundamental. imaging. errors. by. observing. the. interferograms,. misalignment. penalties,. and.
how.alignment.its.into.the.overall.error.budget..In.addition,.we.will.show.the.various.tools.available.
for.aligning.optical.systems.and.discuss.the.special.alignment.considerations.related.to.an.AO.system..
More.importantly,.we.will.discuss.the.procedures.on.how.to.align.and.assemble.the.optics.systemati-
cally,.so.that.a.complex.AO.system.can.be.built.quickly.and.efectively.as.designed.
9.2 Adaptive optics optical System Design considerations
As.with.any.optical.system,.the.AO.system.starts.with.an.object,.with.light.going.through.a.series.of.
optics,.and.inally.ends.at.the.image..he.object.typically.refers.to.a.laser.source.that.provides.illumina-
tion.for.the.biological.samples.and.a.detector.that.is.placed.at.the.image.plane.to.record.the.image.of.
the.samples..Optical.system.design.is.optimized.to.have.the.clearest.image.possible.at.the.detector. 12,13
Several.optical.design.sotware.packages.such.as.Zemax,.CodeV,.and.Oslo.for.optical.system.design.
and. system. optimization. are. available. commercially.. Optical. design. fundamentals. and. principles. are.
covered. by. many. topics. and. also. by. short. courses. at. the. conferences. of. the. International. Society. for.
Optics.and.Photonics.(SPIE).and.Optical.Society.of.America.(OSA)..Optical.design.sotware.companies.
also.ofer.design.classes.and.design.services.if.needed.
AO. refers. to. optical. systems. that. adapt. to. compensate. for. optical. aberrations. introduced. by. the.
medium.between.the.object.and.its.image..his.is.typically.achieved.by.using.a.deformable.mirror.(DM),.
as.described.in.Chapter.8..he.shape.of.the.deformable.mirror.can.be.adjusted.to.compensate.the.wave-
front.errors.in.the.light.path.
Figure.9.1 .illustrates.an.AO.microscope.that.consists.of.two.collimated.laser.sources.at.diferent.wave-
lengths,.a.deformable.mirror.for.aberration.compensation,.a.wavefront.sensor.to.measure.the.wavefront.
error.in.the.optical.path,.scanning.mirrors.for.both. x .and. y .directions.for.two-dimensional.viewing.of.
the.biological.samples,.and.a.photodetector.for.scientiic.image.detection. 14 .hese.components.are.typi-
cally.connected.together.by.relay.telescopes.in.an.AO.system..hese.relay.telescopes.play.important.roles.
in.the.AO.system.
When.designing.an.AO.system,.compared.with.a.typical.optical.system,.special.attention.is.needed.
to.ensure.the.conjugation.of.two.sets.of.planes.to.achieve.correct.phase.compensation.and.thus.a.good.
image. quality.. he. irst. set. of. conjugate. planes. includes. the. illumination. source,. specimen. samples,.
and.a.detector.for.recording.images..he.second.set.of.conjugate.planes.consists.of.a.set.of.pupil.planes,.
which.includes.the.DM,.the.lenslet.array,.the.scanning.mirrors.for.both. x .and. y .directions,.the.pupil.
for.eyepieces.in.the.microscope,.and.the.iris.diaphragm.in.the.human.eye..Conventional.optical.micro-
scopes.require.the.irst.set.of.conjugation,.while.the.second.set.is.uniquely.important.to.ensure.that.an.
AO.instrument.performs.well.
he. conjugation. between. two. pupil. planes. is. accomplished. by. an. afocal. relay. telescope.. he. afocal.
telescope.consists.of.two.lenses.or.two.curved.mirrors.separated.by.the.sum.of.two.focal.lengths. F 1 .+. F 2 ,.
as.shown.is. Figure.9.2 . .he.entrance.pupil.is.usually.placed.at.a.focal.distance. F 1 .away.in.front.of.the.tele-
scope..And.the.resulting.exit.pupil.is.created.at.a.focal.length. F 2 .behind.the.telescope.
he.F-number.of.the.system.is.deined.by.the.focal.length.divided.by.the.diameter.of.the.optics.
F
F
D
F
D
1
in
2
out
.
=
=
.
(9.1)
#
he.telescope.usually.has.collimated.light.in.and.collimated.light.out,.and.the.beam.size.is.changed.
by.the.magniication.of.the.telescope..For.an.afocal.system,.linear.magniication,.which.is.deined.by.the.
ratio.of.the.height.of.the.image.to.the.height.of.the.object,.is.given.by
 
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