Biomedical Engineering Reference
In-Depth Information
he.inal.area.of.consideration.is.the.mirror.coating..Most.devices.are.silver-,.aluminum-,.or.gold-.
coated,. all. of. which. have. acceptable. relectivity. in. the. near-infrared. wavelengths. used. for. excitation.
in. nonlinear. microscopes.. he. gold. mirrors. are. generally. not. as. eicient. in. the. visible. portion. of. the.
spectrum,.and.thus,.for.systems.in.which.the.emission.light.also.relects.of.the.AO.element,.this.may.
be.a.consideration.in.the.mirror.selection..In.particular,.emission.photons.are.precious.as.a.great.deal.
of. efort. has. been. taken. to. obtain. them—and. whereas. losses. on. the. excitation. path. can. generally. be.
compensated.for.by.increasing.the.output.from.the.laser,.this.is.not.possible.for.the.emission.without.
increasing.the.risk.of.sample.damage.and.photobleaching.in.the.case.of.luorescence.
In.summary,.for.a.basic.and.easy-to-operate.system,.a.deformable.mirror.is.currently.the.method.of.
choice.for.an.AO.beam-scanned.microscope..he.mirrors.up.to.around.52.actuators.are.easy.to.control.
and.perform.well,.and.with.the.growth.in.push/pull.mirrors,.this.option.should.be.seriously.considered..
In.terms.of.the.coating,.thought.must.be.given.to.the.range.of.wavelengths.that.the.mirror.is.going.to.
experience.with.the.overriding.consideration.that.emission.photons.are.generally.more.precious.than.
excitation.photons..As.one.is.generally.in.a.nondynamic.situation,.the.speed.of.response.is.likely.to.be.
the.last.factor.in.any.design.consideration.
11.2.4 Practical System
Figure.11.4.shows.the.full.practical.system.for.multiphoton.luorescence.imaging.that.was.used.for.the.
results.presented.later.
he.output.from.a.femtosecond.Ti:Sapphire.(Spectra.Physics.Mai.Tai.and.Coherent.Chameleon.have.
both.been.used.for.the.results.shown.here).was.directed.into.a.pair.of.scanning.galvo.mirrors.that.were.
imaged.onto.each.other.using.75.mm.focal.length.concave.mirrors..For.the.results.presented,.the.laser.
was. generally. centered. on. 830. nm. with. a. power. on. the. sample. of. around. 10. mW.. he. output. from.
the scan. head. was. then. reimaged. and. the. beam. expanded. via. a. polarizing. beam. splitter. and. quarter.
waveplate. onto. the. deformable. membrane. mirror.. For. the. work. shown. here,. an. Okotech. 37. element.
.mirror.and.52.Imagine.Optic.mirror.were.used.interchangeably.as.they.both.have.a.15.mm.diameter.
aperture,.with.the.Imagine.Optic.mirror.having.a.larger.stroke.and.push/pull.capability..he.system.has.
also.been.used.with.a.small.3.mm
2
.32.actuator.mirror.from.Boston.Micromachines.with.equal.success..
he.relection.from.the.mirror.then.passes.back.through.the.waveplate.and.beam.splitter.to.be.relected.
Microscope
Detector
Reimaging and
beam expansion
optics
Beam
scanning
optics
Optical
isolator
Quarter-wave
plate
Femtosecond
laser
Polarizing
beam splitter
Deformable
mirror
Reimaging and
beam expansion
optics
FIGuRE 11.4
Basic.nonlinear.imaging.system.for.multiphoton.or.harmonic.imaging.
