Adaptive Optics System Alignment and Assembly - Adaptive Optics for Biological Imaging - page 164

FIGuRE 9.10 A.collimator.setup.with.iber-coupled.light.input.

into.optical-beam.paths.for.the.purpose.of.checking.alignment.and.characterizing.deformable.mirrors.
or.wavefront.sensors.
An.optical.iber-coupled.source.is.oten.conveniently.used.as.a.collimating.source.in.an.optical.sub-
assembly.process.for.afocal.relay.microscopes.and.wavefront.sensors..It.is.also.an.ideal.source.for.the.
characterization. of. deformable. mirrors. and. wavefront. sensors.. Once. the. AO. system. is. in. operation,.
recalibration.may.be.needed..To.achieve.the.optimized.overall.performance,.it.is.best.to.verify.the.per-
formance.of.the.individual.subassemblies,.adjust.the.subassemblies.if.necessary,.and.inally.tune.up.the.
entire.optical.system.together..he.compactness.of.the.iber-coupled.point.source.allows.the.possibility.
of.verifying.the.individual.performance.of.subassemblies.without.disturbing.the.rest.of.optical.system..
In. troubleshooting,. this. method. provides. an. efective. way. to. igure. out. the. issues. while. avoiding. the.
need.for.realignment.of.all.the.components.
How.well.is.the.beam.collimated.(Figure.9.10)?.here.are.several.tools.for.characterizing.the.beam.
collimation.such.as.shearing.interferometers.and.autocollimators.

9.6.3 Shearing interferometer
Conjugate.planes.are.relayed.by.afocal.telescopes.in.most.AO.imaging.systems. 15 .Both.the.incident.beam.
and.the.output.beam.of.an.afocal.telescope.are.collimated..Afocal.telescopes.are.typically.built.into.an.
optical.subassembly.module.and.tested.independently.to.minimize.alignment.errors.
he.shearing.interferometer.is.a.convenient.tool.to.observe.interference.and.to.use.this.phenomenon.
to.test.the.collimation.of.light.beams.as.well.as.some.low-order.aberrations..he.laser.source.must.have.
a.coherence.length.several.times.longer.than.the.thickness.of.the.shear.plate.to.satisfy.the.basic.require-
ments.for.interference.
A.collimated.beam.would.create.equally.spaced.straight.interference.fringes.parallel.to.a.reference.
line. that. is. determined. by. the. direction. in. which. the. two. wavefronts. are. shited. or. sheered.. When. a.
defocused. beam. is. incident. on. the. shear. plate,. the. screen. shows. tilted. fringes.. Figure. 9.11 . shows. the.
interference.pattern.observed.for.a.diverging,.collimated,.and.converging.beam.