Biomedical Engineering Reference
In-Depth Information
arranged. on. a. square. array. with. 7. mm. spacing.. he. mirror. has. a. 146. mm. clear. aperture.. Since. the.
.mirrors. were. hand. assembled,. the. cost. for. the. mirrors. was. approximately. $1000. per. actuator. (Ealey.
1994),.resulting.in.DM.that.costs.in.the.hundreds.of.thousands.of.dollars.
he.irst.AO.DMs.for.astronomy.were.hand.assembled.using.piezoelectric.or.electrorestrictive.actua-
tors.(PZT.[piezoelectric].or.PMN.[electrorestrictive]).that.were.bonded.to.either.segmented.mirrors.or.
a.thin.glass.facesheet.mirror..Since.piezoelectrics.have.a.typical.displacement.of.a.few.angstroms/volt;.
they.are.usually.fabricated.as.discs.and.stacked.in.series.to.obtain.a.displacement.of.few.micrometers.
for. 100. V.. One. challenge. for. piezoelectrics. are. that. they. exhibit. a. hysteresis. phenomenon,. where. the.
displacement. depends. on. the. past. history. of. actuator. displacements.. his. tends. to. slow. down. a. mir-
ror.under.closed-loop.feedback.control.since.it.must.hunt.for.the.demanded.position.and.makes.go-to.
.open-loop. positioning. a. challenge.. Piezoelectric. mirrors. with. 37-941. actuators. at. 7. and. 5. mm. spac-
ings.have.been.manufactured.by.the.Xinetics.corporation..hese.provide.3-8.μm.of.stroke..Northrop.
Grumman/AOA.Xinetics.has.recently.designed.a.“photonics.module”.approach.where.the.grid.of.the.
actuators. is. machined. out. of. a. single. piezoelectric. ceramic. substrate.. his. enables. a. smaller. actuator.
pitch.of.2.5.and.1.0.mm.and,.therefore,.high-density.actuation.over.a.given.size.mirror..A.continuous.
glass.facesheet.is.bonded.on.top.of.the.module.and.subsequently.polished.and.coated.to.complete.the.
high-density.DM..Xinetics.has.delivered.DMs.based.on.this.technology.containing.1000.and.4000.chan-
nels.at.a.1.mm.spacing.and.37.and.349.channels.at.a.2.5.mm.spacing..A.photo.of.a.high-density.module.
with.a.1.mm.pitch.is.shown.in.Figure.8.16..he.Cilas.corporation.in.France.is.also.developing.a.high-
stroke,.high-order.DM..A.9.×.9.prototype.developed.under.a.design.study.for.the.30-meter.telescope.
(TMT).is.shown.in.Figure.8.17..he.TMT.AO.system.baseline.design.requires.two.DMs.with.63.×.63.and.
75.×.75.arrays.of.actuators.
FIGuRE 8.16
Xinetics.high-density.(32.×.32).photonic.module..he.actuator.pitch.in.this.image.is.1.mm..he.
array.size.is.scalable.to.9216.channels..(Credit:.John.A..Wellman,.David.D..Pearson,.Jefrey.L..Cavaco,.Northrop.
Grumman/AOA.Xinetics.)
FIGuRE 8.17
Cilas. high-stroke,. high-order. deformable. mirror. prototype. being. developed. for. 30. m. telescope..
Shown.here.is.a.9.×.9.subscale.prototype.DM.with.a.stroke.of.11.μm,.surface.latness.of.13.nm.RMS,.and.hysteresis.
of.5%-6%..(Credit:.Compagnie.Industrielle.des.Lasers.[CILAS].)
