Biomedical Engineering Reference
In-Depth Information
From.this.brief.introduction,.it.is.clear.that.AO.potentially.has.a.signiicant.role.in.optimizing.and.
improving.the.performance.of.the.beam-scanned.nonlinear.microscopes,.and.with.their.inherent.ability.
to.image.at.depth.in.live.samples,.the.practical.implementation.of.such.systems.will.now.be.considered.
11.2 instrumentation
In.this.section,.we.will.consider.the.basic.practical.requirements.needed.to.include.an.AO.element.into.
the.system..Initially,.the.core.elements.of.such.a.microscope.will.be.examined.before.moving.on.to.the.
speciic.details.of.incorporating.an.AO.element.into.the.optical.path..hroughout,.we.will.consider.the.
AO.element.to.be.relective,.although.it.is.appreciated.that.liquid.crystal.devices.are.available.that.can.
operate.in.a.transmissive.mode..he.basic.principles.of.design.outlined.later,.however,.apply.in.all.cases.
11.2.1 Basic Beam-Scanned System
he. basic. optical. system. for. a. beam-scanned. microscope. is. shown. in. Figure. 11.1,. and. the. excitation.
path.is.common.for.both.linear.and.nonlinear.excitation.systems..he.main.diference.between.the.two.
excitation.modes,.apart.from.the.coatings.required.on.the.dichroic.elements.and.ilters,.is.that.in.a.con-
focal.microscope,.the.signal.light.needs.to.be.descanned.before.passing.through.the.confocal.pinhole.
and.reaching.the.detector..In.a.nonlinear.microscope,.as.will.be.discussed.later,.the.signal.light.does.not.
have.to.be.descanned.
he.light.from.the.laser.source.is.initially.directed.onto.the.scanning.system,.and.the.spot.size.of.the.
beam.is.matched.to.the.scanning.optics..For.most.nonlinear.microscopes,.the.scanning.is.undertaken.
using. a. pair. of. scanning. mirrors. that. eventually,. under. computer. control,. raster-scan. the. beam. over.
the.sample..It.is.possible.to.use.acousto-optic.modulators.to.undertake.the.beam.scanning,.which.does.
result.in.fast.scanning,.but.the.complication.is.that.the.material.used.in.such.devices.tends.to.lengthen.
the.laser.pulse,.and.thus.pulse-length-dispersion.compensation.is.required.
In.a.scanning.mirror.system,.the.mirrors.can.be.conigured.in.two.ways:.close.coupled.or.reimaged..
In.the.close-coupled.coniguration,.the.mirrors.are.placed.as.close.together.as.possible,.with.one.mirror.
being.directly.relected.onto.the.other..he.advantage.of.such.an.optical.design.is.clearly.that.the.scan.
head.can.be.small.and.compact;.the.disadvantage.is.that.that.the.beam.on.the.second.scanner.moves.
Control
electronics and
computer
Femtosecond
laser
Beam
scanner
Microscope
Detectors
FIGuRE 11.1
Basic.components.of.a.beam-scanned.nonlinear.microscope.
