Biomedical Engineering Reference
In-Depth Information
are.centered..If.not,.adjust.the.positions.of.optical.components.so.that.the.dot.falls.on.the.center.of.the.
elements..An.iris.provides.a.quick.and.efective.way.to.carry.out.coarse.alignment,.and.visualization.
makes.the.process.easy.
9.6.7 Machine target/Fiducially
Many.components.are.diicult.to.align.based.on.their.features..In.such.cases,.adding.reference.features.
can.greatly.simplify.the.alignment..For.example,.microlens.arrays.with.secondary.alignment.features.
etched.into.the.substrate.are.very.useful.for.minimizing.alignment.errors.in.rotation..An.easy-to-align,.
nonfunctional.reference.feature.that.is.precisely.registered.to.the.functioning.part.of.the.optic.can.be.an.
essential.part.of.an.optical.alignment.process.
9.7 Ao System-Speciic considerations
9.7.1 Deformable Mirrors on Kinematic Mounts
A.DM.in.general.is.not.optically.lat.in.its.natural.state..It.is.recommended.to.use.a.lat.mirror.in.the.
position.of.the.DM.to.perform.optical.alignment.of.the.AO.system..Otherwise,.the.optical.alignment.
may.not.be.done.properly,.as.DMs.typically.have.some.curvature,.and.the.curvature.might.even.be.of-
centered.or.irregular.
Furthermore,. deformable. mirror. manufacturing. takes. substantial. engineering. and. research. efort.
to. deliver. high-quality. DMs,. depending. on. the. speciications.. he. lead. time. is. typically. fairly. long..
Quite. oten,. DMs. may. not. be. available. when. the. system. alignment. and. integration. are. performed..
In. addition,. DMs. need. to. be. changed. or. ixed. if. there. are. electrical,. mechanical,. or. reliability. issues.
when.doing.scientiic.imaging.of.biological.samples.ater.the.imaging.system.is.complete.and.totally.
operational.
he.DM.should.be.mounted.and.aligned.using.a.removable.kinematic.mount.with.a.permanent.kine-
matic.base.with.interchangeable.tops..he.DM.and.the.lat.mirror.should.each.be.mounted.on.separate.
kinematic.top.plates.and.coaligned.in.both.position.and.angle,.so.that.they.can.be.interchanged.oline..
his.way,.one.can.integrate.and.troubleshoot.the.AO.system.without.worrying.that.previous.work.in.
alignment.will.be.lost.
Obviously,. repeatability. is. essential. to. ensure. the. performance. of. AO. systems.. One. needs. to. use.
high-precision.kinematic.mounts.for.DMs.and.lat.mirrors.to.achieve.the.targeted.positions.over.many.
attempts. and. over. time.. Figure. 9.12 . shows. an. example. of. kinematic. mounts.. F igure. 9.12a . shows. the.
separate.top.and.bottom.plates.with.optics.mounted.on.the.top.plate.and. Figure.9.12b .shows.how.the.
top.plate,.bottom.plate,.and.optics.are.mounted.together..he.top.mounting.plate.and.the.bottom.base.
plate. of. the. kinematic. base. are. magnetically. coupled,. and. the. top. plate. can. be. inserted. or. removed.
typically. with. 10. μrad. precision. and. repeatability.. Repeatability. of. the. kinematic. mounts. should. be.
measured. and. veriied. before. integrating. the. subassembly. together. with. the. alignment. of. the. whole.
AO.system..
9.7.2 Shack-Hartmann Wavefront Sensor Subassembly
he.wavefront.sensor.(WFS).measures.the.aberration.in.the.optical.path.to.provide.the.input.signal.to.
the.DM,.so.that.the.DM.can.be.shaped.by.the.control.electrodes.to.cancel.out.the.wavefront.error.in.the.
beam.path..It.is.one.of.the.most.important.elements.in.an.AO.system..Its.measurement.sensitivity.and.
accuracy.determines.the.overall.performance.of.the.AO.system.and.thus.the.image.quality.of.biological.
samples.
he. Shack-Hartmann. WFSs. consist. of. an. optical. source,. a. lenslet. array,. and. a. CCD. camera.. he.
lenslet. array. is. a. two-dimensional. array. of. small. lenses. with. the. same. diameters,. curvatures,. and.
 
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