Figurecorrec*onofmirrorsubstrates

OWGFigurecorrec*onsubgroupMay22nd,2017

TechnicalInforma*onExchangemee*ngHuntsville,AL

Speaker:BrandonChalifoux

Figurecorrec*onsub-groupRyanAllured Harvard-SAO

BrandonChalifoux MassachuseOsIns*tuteofTechnology

LesterCohen Harvard-SAO

CaseyDeRoo Harvard-SAO

ManelErrando WashingtonUniversity

CharlyFeldman UniversityofLeicester

MouradIdir BerkeleyNa*onalLabs

PaulReid Harvard-SAO

MarkSchaOenburg MassachuseOsIns*tuteofTechnology

EricSchwartz Harvard-SAO

MelUlmer NorthwesternUniversity(NW)

DavidWindt Reflec*veX-RayOp*cs,LLC.(RXO)

Purposeoffigurecorrec*onWhileitmaybepossibleto:

•  Createasetofperfectmirrors,•  Coatthemwithoutdistor*on,•  Alignandmountthemwithoutdistor*on,and•  Launchatelescopewithnoaddi*onalerrors,

thisisnotguaranteed!

Mirrorcorrec*onmayberequiredtoachievethemissionrequirements.Thecorrec*onsmaybeappliedatvariouspointsintheop*calassembly

fabrica*onprocesstoaddressdifferenterrorsources.

Figurecorrec*onmethods

Curvature-basedmethodsbehaveslikealow-passfilter.Higherspa*alfrequencyerrorsaredifficulttocorrectoruninten*onallyintroduce.

Height-based methods behave like a high-pass filter.Caremust be taken to avoid introducing higher spa*alfrequency errors, but high-frequency errors may, inprinciple,becorrected.

Height-basedmethods Curvature-basedmethods

Materialremovaland/or

Materialaddi*on

Thinstressedfilm

Op#calsurface,uncorrected Op#calsurface,uncorrected

Op#calsurface,corrected

Op#calsurface,corrected

𝜃= 𝜕ℎ/𝜕𝑧  →ℎ𝑖𝑔ℎ 𝑝𝑎𝑠𝑠 𝑓𝑖𝑙𝑡𝑒𝑟𝜃=∫𝜅 𝑑𝑧 →𝑙𝑜𝑤 𝑝𝑎𝑠𝑠 𝑓𝑖𝑙𝑡𝑒𝑟

Curvaturechangedviastressedfilm

Heightchangedvia

ListofapproachesbeingstudiedMethod Ins+tu+on(s) Methodtype

Differen*aldeposi*on MarshallSpaceFlightCenter,Reflec*veX-rayOp*cs,LLC

Height

Ionbeamfiguring INAFOsservatorioAstronomicodiBrera Height

Piezo-electricfilms SAO,PennStateUniversity Curvature

Magneto-stric*vefilms NorthwesternUniversity Curvature

Ionimplanta*onstress MassachuseOsIns*tuteofTechnology Curvature

Stress-controlledmetalfilms NorthwesternUniversity Curvature

Referencesforeachapproachwillbegivenincorrespondingslide

Whentoperformfigurecorrec*on?

•  Latercorrec*onmayenablecorrec*onofmoreerrors•  Earliercorrec*onmaybeeasiertoperformmetrology

•  Somemethods(e.g.,ionimplanta*on)areprobablynotfeasibleoncethemirrorsaremounted.

•  Othermethods(e.g.,PZTfilms)mayallowcorrec*onspost-launch,butpost-launchmetrologyisachallenge.

1Ddifferen*aldeposi*on

Recentpublica*onandsourceofallimages:K.Kilaru,etal.Progressindifferen#aldeposi#onforimprovingthefiguresoffull-shellastronomicalgrazing-incidenceX-rayop#cs.Proc.SPIE9603(2015)

SpuOeringheadwithinfull-shell

mirror

Correc*onofmid-frequencyerrorsinasinglemeridianshows~2ximprovementforasinglecorrec*onstage.SlopemeasurementstakenwithLongTraceProfiler,confirmedbyx-raytes*ng.

Mirrortransla*onspeedcontrolsspuOerdeposi*onateachpointonmirror

2Ddifferen*aldeposi*on

Recentpublica*on:D.L.WindtandR.Conley,Two-dimensionaldifferen#aldeposi#on:figurecorrec#onofthin-shellmirrorsubstratesforX-rayastronomy.Proc.SPIE960396031H(2015).

Prototype“1-finger”dynamicaperture.

DynamicApertureconcept.

Localdeposi*onratecontrolleddynamicallywithvariableapertures;substratespeedconstant.

Thisenablesmul*plemeridianstobecoatedinparallel,withagoalofincreasingthroughput.Differen*alerosionmayalsobepossible.

Ionbeamfiguring

Recentpublica*ons:M.Ghigo,etal.IonfiguringoflargeprototypemirrorsegmentsfortheE-ELT.Proc.SPIE9151(2014).M.Civitani,etal.Ionbeamfiguringthinglassplates:achievementsandperspec#ves.Proc.SPIE9905(2016).

MaterialisremovedbyspuOeringatomsfrommirrorsurface,usinganiongun.Materialremovalateachpointiscontrolledbychangingdwell*me.

IBFresidualerrorona~1mdiameter[thick]mirror,aoer3runs.Image:Ghigo,etal.(2014).

IBF-inducedchangeinthicknessofaD-263glasssheet.Image:Civitani,etal.(2016).

Thinmirrorswithinternalstresswillalsodeformduetosurfaceerosion.ThiseffectwasobservedinresponsetotheaboveIBF.

Curvature-basedmethods

Determiningintegratedstressprofiletoprovidecorrec*onistypicallydonebycalcula*ngormeasuring“influencefunc*ons”ofvariousactuators,and

inver*ng

𝑆↓𝑒  = 𝐸ℎ↓𝑠 ↓↑2 /6(1−ν)  ∆𝜅↓𝑒 

Substrateproper*es

Measuredcurvature

Integratedstress

Stoney’sequa*on

E Elas*cmodulusν Poisson’sra*ohs SubstratethicknessΔκe EquibiaxialchangeincurvatureSe EquibiaxialIntegratedstress

Inacurvedsubstrate,changeincurvatureisroughlyrelatedtointegratedstress.

yx

Stressstatesonasurface

σxσy

τxyσe

σe

Equibiaxialstress:•  Moremethodstoapply•  Filmstresseffec*velybecomesascalar•  Reliesonover-constrainedmoun*ng•  Correc*ngfilmstresserrorscouldalways

beaccomplishedwithequibiaxialstress.

Generalstress:•  Fewermethodstoapply•  Threecomponentsofstressthatneedto

becontrolled•  Correc*ondoesnotrequireover-

constrainedmoun*ngscheme

Equibiaxialstressstateinadifferen#alsurfaceelement.

Generalstressstateinadifferen#alsurfaceelement.

Substratewithadifferen#alsurfaceelementoutlined

Piezo-electricfilms

Currentissuesunderstudy:•  Filmstackstresscontrol•  PZTlong-termstability•  Methodsofon-orbitstrainand

temperaturemonitoring•  Electroniccontrolstrategies

Stresstype Equibiaxialonly

Max.integratedstress

~150N/m(tensile)

Substratecompa*bility

Silicon,glass

LeadZirconiumTitanate(PZT)filmsundergostrainpropor*onaltoanappliedelectricfield.

Recentpublica*on:R.Allured,etal.Laboratorydemonstra#onofthepiezoelectricfigurecontrolofacylindricalslumpedglassop#c.Proc.SPIE9905(2016).

Fabricated(Leo)andMounted(Right)AdjustableOp*c.

HighFidelityDeterminis#cFigureControlUnit,Rev.3

Magneto-stric*vefilms

Poten*alissuesunderstudy:•  Stress(orstrain)profile•  Long-termstability•  Viabilityofmagne*cally-hard

films•  Stresscontroloffilmstack•  Onorbitcorrec*ons[tricky]

Magneto-stric*vefilms(e.g.,Terfanol-D)undergostrainpropor*onaltoanappliedmagne*cfield.Amagne*cally-hardmaterialwouldbeneededtoretainthefieldinthemagneto-stric*vematerial.

Stresstype Non-equibiaxial

Max.integratedstress

~+10..-50N/m(direc*on-dependent)

Substratecompa*bility

Magne*cmaterials,siliconandglassunderinves*ga*on

Recentpublica*on:X.Wang,etal.Deforma#onofrectangularthinglassplatecoatedwithmagnetostric#vematerial.SmartMaterialsandStructures,25(8),2016.

ImagefromX.Wang,etal.2016.

~0.2microns/~3mmretainedaoerfieldremoval

Ionimplanta*onstress

Currentissuesunderstudy:•  Stress-doseprofilefordifferentmaterials•  Short-termstressrelaxa*onandlong-

termstabilityindifferentmaterials•  Surfaceroughening

Stresstype Silicon,SiO2:EquibiaxialEagleXG,D-263glass:gen.

Integratedstressrange

Silicon:-100N/m(comp.)SiO2:-300N/m(comp.)to

+1200N/m(tens.)

Substratecompa*bility

Silicon,glass

Energe*cionsimplantedintoasubstratecausemorphologicalchangesandstressrelaxa*on.

SchoOD-263glass

ImagefromChalifoux,etal.2016.

Recentpublica*on:B.Chalifoux,etal.Gasbearingslumpingandfigurecorrec#onofX-raytelescopemirrorsubstrates.Proc.SPIE9905(2016).

Stress-controlledmetalfilms

Currentissuesunderstudy:•  Stressresolu*onandaccuracy•  Spa*alresolu*onandaccuracy

Stresstype Equibiaxial

Integratedstressrange

-250…+250N/m

Substratecompa*bility

Silicon,glass

StressinmetalfilmsduringmagnetronspuOeringmaybecontrolledbyadjus*ngsubstratebiastochangetheenergyofimpac*ngions.

Recentpublica*on:Y.Yao,etal.Stressmanipulatedcoa#ngforfigurereshapeoflightweightX-raytelescopemirrors.Proc.SPIE9603(2015).

Othergroupsalsoinves*ga*ngusingfilmstresstocorrectfigure:•  NASAMSFC•  NASAGSFC•  RXO

Conclusions

•  Twotypesofapproachesareunderdevelopment:o  Height-basedmethodsmaybemosteffec*vefor

correc*ngmid-frequencyerrorso  Curvature-basedmethodsmaybemosteffec*vefor

correc*nglow-frequencyerrors•  Theeffec*venessofcurvature-basedmethodsmaybe

linkedtothemoun*ngscheme,ifonlyequibiaxialstressmaybeapplied.

•  AnymethodunderdevelopmentwouldneedtobeindustrializedtobeviablefortheLynxmission.