Biomedical Engineering Reference
In-Depth Information
9.5 optical Alignment
Alignment.of.complex.AO.systems.can.be.quite.challenging..Multiple-beam.paths.with.folds,.several.
sources.at.diferent.wavelengths,.of-axis.elements,.cylindrical.optics,.aspheric.lenses,.and.tight.toler-
ances.all.can.cause.potential.alignment.issues..AO.components.such.as.lens.arrays,.sensors,.and.DMs.
deserve.special.attention.in.the.alignment.process.
he.AO.microscope.in.
Figure.9.1
.
shows.an.example.of.a.complex.optical.system.including..multiple-.
beam.paths.with.folds..Two.laser.input.sources.with.two.diferent.wavelengths.are.coupled.into.the.
AO.system.by.beam.splitters..here.are.mainly.three.functional.optical.paths.in.this.example..One.
path.delivers.the.light.to.the.biological.sample;.one.path.is.for.measuring.the.wavefront.errors.using.
a. wavefront. sensor;. and. one. path. is. for. image. detection. with. a. detector.. All. three. paths. share. the.
DM,.scanners,.microscope.objective,.and.pupil-relay.telescopes.between.them.
It.can.be.diicult.to.decide.where.to.start.and.which.methods.to.use.when.dealing.with.a.complex.
optical.system..But.alignment.does.not.need.to.be.an.overwhelming.task.even.if.the.system.is.complex..
When.planning.the.alignment.and.assembly.processes,.a.number.of.general.strategies.as.well.as.utiliza-
tion.of.well-known.alignment.tools.and.optical-instrument.feedback.can.be.very.helpful.
9.5.1 Using a Full-Size Mechanical Layout
It.is.very.useful.to.print.out.a.full-size.drawing.of.the.optical.design.and.place.it.on.top.of.the.optical.
breadboard.or.optical.table..If.the.mechanical.design.has.been.done.using.a.CAD.tool,.print.out.a.full-
size.drawing.of.the.system.layout.with.the.bases.of.the.optomechanical.ixtures.and.mounts.as.well..his.
will.provide.a.quick.idea.on.how.the.system.its.together.and.if.it.is.what.the.designers.or.scientists.have.
intended.
Tape.the.full-size.drawing.to.the.optical.table.and.then.place.the.optical.components.and.optome-
chanical. mounts. on. the. table. over. their. footprint. on. the. drawing.. his. will. provide. a. direct. view. on.
whether.there.is.enough.work.space.available.to.allow.hands.in.between.the.components.for.alignment.
adjustment.in.a.compact.system..If.there.are.any.issues,.modifying.the.design.and.layout.before.aligning.
the.complete.optical.system.will.save.a.lot.of.time.and.efort.
his.method.also.provides.an.efective.way.to.quickly.place.the.components.very.close.to.the.nomi-
nal.design.and.enable.one.to.tell.if.the.integration.is.starting.to.deviate.from.the.nominal.design..Fine.
optical.alignment.and.adjustment.are.still.needed.based.on.optical.feedback..he.paper.can.be.removed.
when.necessary.to.access.the.table's.threaded.holes.and.eventually.can.be.removed.entirely.
9.5.2 Use Mechanical constraints
As.discussed.in
.
Section.9.4.4
,.a.cage,.a.rail,.or.a.stage.assembly.system.is.one.of.the.most.efective.and.
inexpensive.alignment.tools.to.prealign.optical.components.along.the.optical.axis.in.either.one.direc-
tion.or.two.directions..By.putting.the.complexity.into.the.metal,.the.assembly.process.becomes.much.
simpler;.all.that.is.needed.is.to.place.the.optical.component.in.its.appropriate.location..When.there.are.
multiple.paths.and.folds.in.a.system,.these.metal.mounts.may.not.be.able.to.integrate.all.the.components.
together..Nonetheless,.these.tools.can.be.used.to.build.subassemblies.of.the.more-complicated.system.
and.partially.simplify.the.system.integration.process.
When.tolerances.are.too.tight.for.drop-in.assembly,.this.basic.approach.is.still.valuable.for.get-
ting.components.close.to.their.optimum.position.and.limiting.their.deviation.from.their.nominal.
positions. during. the. alignment. process.. When. mechanical. constraints. limit. the. deviation. of. an.
optic's. position. from. the. ideal. location,. component. adjustments. are. easier. and. time-consuming.
gross.misalignments.are.prevented..Commercial.vendors.are.increasingly.expanding.their.produc-
tion. lines. so. that. ine. adjustments. can. be. made. in. all. six. degrees. of. freedom. with. these. precision.
building.blocks.
