Biomedical Engineering Reference
In-Depth Information
that.the.lenslet.array.plane.is.in.focus..If.not,.adjust.the.position.of.WFS.subassembly.longitudi-
nally.or.axially..Typically.the.alignment.marks.or.iducials.on.the.lenslet.array.are.very.helpful.to.
achieve.this.goal.
.
13.. he.detector.path.should.be.installed.last..In.the.case.of.a.PMT.assembly,.center.the.detector.sub-
assembly.and.make.sure.that.image.of.the.focusing.lens.for.the.PMT.shows.up.sharply.in.the.pupil.
plane.camera..Pinhole.positions.are.usually.optimized.for.a.single.wavelength.and.typically.need.
to.be.readjusted.depending.on.the.luorescence.wavelength.from.the.science.samples,.especially.
when.several.wavelengths.are.used.in.imaging..he.pinhole.size.and.location.should.be.optimized.
for.each.individual.wavelength.for.overall.performance.
9.9 optical System Performance improvement/troubleshooting
It.may.take.several.iterations.to.achieve.high.performance.of.the.AO.system.including.improvement.in.
the.control.algorithms.for.wavefront.sensing.and.reconstruction;.ine.adjustment.for.the.optical.system.
alignment;. and. minimizing. the. electrical,. mechanical,. and. optical. noises. while. performing. scientiic.
measurements..In.this.section,.we.focus.on.how.to.improve.the.system.performance.related.to.better.
optical.alignment..We.also.discuss.what.needs.to.be.done.if.the.acquired.images.are.fuzzy.or.degraded.
images.are.acquired.
.
1.. Starting.with.coarse.alignment—making.sure.that.spot.sizes.on.optical.components.are.centered.
and.the.optical.beam.is.going.through.all.the.optical.trains.without.being.blocked.or.unintention-
ally.vignetted.by.any.optomechanical.mounts.
.
2.. If.there.are.collimated.spaces.in.the.design,.check.for.collimation.using.a.shear.plate.and.observe.
the.shear.fringes..he.DM,.WFS,.detector,.and.scanners.are.all.typically.in.the.collimated.space..
Check.all.relay.telescopes.to.see.if.the.incoming.collimated.beam.that.passes.through.the.relay.
telescopes.is.still.well.collimated.ater.the.telescope.
.
3.. Check.the.pupil.camera.to.see.if.all.the.related.conjugate.planes.can.be.observed.with.clear,.sharp.
images.so.that.there.is.a.correct.phase.correlation.in.AO.system..If.a.scanner.is.involved.and.is.not.
positioned.correctly.at.the.conjugate.plane,.the.image.on.the.CCD.camera.will.move.around.when.
the.scanner.is.in.operation..Otherwise,.the.image.of.the.scanner.should.remain.stationary.
.
4.. If.there.is.any.scattering.of.light.in.the.system,.place.an.iris.or.an.aperture.at.the.focal.point.of.
the.relay.telescope.to.ilter.out.the.high-order.scattered.light..he.size.of.the.aperture.should.be.
adjusted.to.let.the.main.beam.pass.through.while.blocking.the.high-order.scattering..his.will.
signiicantly.increase.the.signal-to-noise.ratio.
.
5.. Each. subassembly. should. be. independently. calibrated. and. adjusted.. A. compact. iber. optics-.
coupled.laser.source.can.be.especially.useful..It.can.be.inserted.into.a.inished.system.to.check.
the.performance.of.the.part.of.optical.path.either.as.a.point.source.or.a.collimated.source..his.
way,.problems.resulting.from.the.optical.subassembly.or.functioning.path.can.be.identiied.and.
resolved. quickly.. In. addition,. a. perfect. point. source. or. well-collimated. source. would. make. the.
calibration.or.alignment.much.more.accurate.instead.of.using.the.optical.beam.that.has.accumu-
lated.aberrations.from.the.upstream.optics.
.
6.. Place.a.collimated.beam.in.front.of.the.WFS,.and.measure.the.aberrations.in.the.beam..he.aber-
ration.measured.by.the.WFS.should.be.very.small—close.to.zero..Otherwise,.the.WFS.needs.to.be.
adjusted.and.recalibrated.
.
7.. he. DM. should. be. lattened. oline. using. an. interferometer. before. being. inserted. into. the. AO.
optical.system..To.conirm.the.latness,.a.point.source.can.be.inserted.at.the.image.plane.and.used.
to.measure.the.latness.of.the.DM.with.the.WFS.in.the.system..Even.though.the.DM.is.mounted.
on.a.high-precision.interchangeable.top.plate.with.high.repeatability,.in.sensitive.measurements,.
the.AO.system.most.likely.still.needs.recalibration.for.optimized.performance.
