Biomedical Engineering Reference
In-Depth Information
Babcock.proposed.to.compensate.for.the.turbulence.of.the.atmosphere.by.measuring.the.wavefront.
aberrations.from.a.guide.star.and.correcting.them.with.an.early.form.of.a.DM.that.was.then.used.in.an.
electronic.projector.called.an.Eidophor.(Hornbeck.1998)..he.Eidophor.used.a.spatial.light..modulator.
principle.. It. consisted. of. a. thin. layer. of. oil. on. a. conducting. mirror.. With. a. raster. scanned. beam. of.
electrons.from.a.cathode.ray.tube,.a.charge.can.be.deposited.on.the.surface.of.the.oil.layer.in.a.pattern..
he.attractive.force.between.the.charge.and.the.conducting.substrate.deforms.the.surface.of.the.oil.as.
shown.in.Figure.8.8..he.deformation.of.the.oil.causes.a.variation.of.the.thickness.above.the.mirror.so.
that.light.traversing.the.oil.and.relecting.of.the.mirror.experiences.a.varying.optical.path.length..In.the.
Eidophore.projection.application,.the.charging.over.a.portion.of.the.surface.of.the.oil.formed.a.schlieren.
grating..his.phase.grating.was.used.to.difract.light.relecting.of.of.the.mirror.below..A.dark.pixel.was.
created.in.the.projection.system.when.there.was.no.charge.deposited.and,.therefore,.no.grating.and.no.
difraction.and.a.bright.pixel.formed.when.there.was.difraction..More.recently.a.liquid.deformable.mir-
ror.has.been.demonstrated.that.is.based.on.based.on..electrocapillary.actuation.(Vuelban.2006).
he. “seeing. compensator”. that. Babcock. proposed. to. use. the. Eidophor. for. wavefront. correction. is.
shown. schematically. in.
Figure. 8.9
.
. Light. from. a. star. is. brought. to. a. focus. at. F.. A. ield. lens. images.
the. input. pupil. of. the. telescope. onto. the. Eidophor,. which. is. formed. on. an. of-axis. parabolic. mirror..
he.relected.light.is.brought.to.a.focus.on.a.rotating.knife.edge.at.the.focal.point.of.a.second.of-axis.
No diffraction
Oil
Conducting
mirror
Substrate
Dark pixel
Diffracted light
Deposited charge
Substrate
Bright pixel
FIGuRE 8.8
Spatial.light.modulator.used.in.the.Eidophor.projection.system..A.thin.layer.of.oil.is.deposited.over.
a.grounded.conducting.mirror.that.has.been.deposited.on.a.substrate..
Top
:.No.charge.has.been.deposited.on.the.oil.
layer,.so.the.optical.path.length.for.all.light.rays.is.the.same.and.light.relects.of.of.the.mirror,.creating.a.dark.pixel.
in.the.Eidophor.projection.system..
Bottom
:.When.a.sinusoidal.charge.pattern.has.been.deposited.with.a.cathode.ray.
tube,.the.charge.is.attracted.to.the.conducting.mirror,.deforming.the.surface.of.the.oil.layer.into.a.sinusoidal.pat-
tern..Light.traversing.the.deformed.oil.layer.and.relecting.of.of.the.mirror.surface.experiences.a.spatially.varying.
optical.path.length,.causing.the.light.to.difract..he.difracted.light.forms.a.bright.pixel.in.the.projection.system..
(Courtesy.of.Texas.Instruments.)
