march 18, 2004tips – olivia lupie1 wfc3 filter testing, modeling, designing ghosts (spurious...

March 18, 2004 Tips – Olivia Lupie 1

WFC3 Filter Testing, Modeling, DesigningWFC3 Filter Testing, Modeling, Designing

Ghosts (spurious reflections) in some UVIS filters were discovered during first ambient calibration of WFC3

Ambient Cal Filter Ghost Characterization – T. Brown, O. Lupie

GSFC Lab Setup (spare and proto-type filters): Randy Telfer (Orbital, GSFC), Ray Boucarut (GSFC)

Filter Modeling: Dave Kubalak, Randy Telfer, (Orbital), Bill Eichhorn (GSFC)

GSFC Lab Data Reduction , Analysis: Sylvia Baggett, Olivia Lupie

Vendors: Barr Associates, Omega Optical

UVIS Ambient Nano Calibration – G. Hartig, N. Reid, S. Baggett, T. Brown, H. Bushouse, B. Hilbert, O. Lupie

TEAMTEAM


Parameters Used to Spec a Filter Pre-Install Test

Spectral Requirements

Wavelength tolerances xCentral wavelength xSlopes of bandpass sides/wings xOut of Band Rejection Longward of Passband xOut of Band Rejection Shortward of Passband xRipples in Passband xScattered Light

Angle of Incidence xFocus shift and Filter thickness xAnti Reflection Coatings xOperational Temperature xDimensions

mechanical size, shape xClear Aperture size xWedge - for transmitted wavefront - substrates xOptical Figure xSurface quality

Transmitted Wavefront xScratch-Dig-blemishes xAdhesion of coating xHardness of coating xHumidity xConstruction

Adhesive bondline xCoating materials - general xAdhesives xEdge Sealants xEnvironmental Requirements x not usually tested before install -instrument specific, costly, schedule prohibitive

Parameters Used to Spec a Filter to Vendors

Vendor uses specs to design a filter:•Determine substrates, coatings, coating thicknesses, deposition process.•Provide model of throughput, out of band rejection, spatial uniformity•Model is accepted or rejected•Vendor builds the filter


57.3 mm

UVIS CCDUVIS CCDFilter WheelFilter Wheel11

Filter WheelFilter Wheel66

Filter WheelFilter Wheel1212

Edge Rays DefineEdge Rays DefineField-Of-ViewField-Of-View

ImageImageImage RaysImage RaysInstantaneous BeamInstantaneous BeamFootprintFootprint

14 m

m

10 m

m

~3o

WFPC-1’s SOFA – 12 wheels • Converging instantaneous beam footprint • F31 beam• +/- 3 degree range for field angles

WFC3 Filter Testing, Modeling, DesigningWFC3 Filter Testing, Modeling, Designing


F225 Transmission Theoretical vs Measured

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Wavelength (nm)

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nsm

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desired bandshape

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Wavelength (nm)

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Theoretical Transmission

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Wavelength (nm)

"T

ran

sm

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sht1

sht2

AR Coating

met block

desired bandshape


Theoretical Reflectivity

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Wavelength (nm)

Refl

ecti

vit

y

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AR Coat

met block refl

Theoretical Transmission

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Wavelength (nm)

"T

ran

sm

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AR Coating

met block

desired bandshape

Spectral Shaping of the FilterSpectral Shaping of the Filter


Modeling Status

11

22

33

44

Anti-reflectionAnti-reflection

Shortpass 1Shortpass 1

Substrate #1

Metal blocker(aberrations –astigmatism)

Substrate #2

Shortpass 2Shortpass 2

Transmitted1st order ghostsaberrated

2nd order ghostsdoubly aberrated

Possible Model of F225W Ghosting (modelers: Randy Telfer, Dave Kubalak)

Aberrations result from reflections from metal blocker

Substrate 1.1 mm

GAP (0.38 mm)

Substrate 3.0 mm

Bond &Spacer

Air-GapConstruction

Ideally – all surfacesperfectly parallel

Airgap replaced adhesive – adhesive reduced throughput and introducemajor spatial dependence across filter


F218W

F218W

F225W

F225W

F300X

F606X

<1% in white light<1% in white light

<1% in white light<1% in white light> 10% in white light> 10% in white light > 10% in white light> 10% in white light

(analysis T. Brown with ICAL team)

Flight Filter Ghosts (worst cases)

Some wide band UV air-gap filters exhibited large amplitude ghost images:


Faint pointghosts at~0.1% of theprimary imageintensity, moving little with fieldposition.Larger donutghosts at 0.3%,movingsignificantly.

0.02%0.3%

0.06%0.08%

0.13%

0.08%test artifact

Flight – F606W in WFC3White light – 5 micron fiber

Faint pointghosts at~0.01% of theprimary imageIntensity. Fieldangle check inwork..*white lightghosts 10xfainter than Flight – however more testing is needed to verify.

Spare – F606W – labCohu, 10 micron fiberXenon Lamp

Lab Measurements of Spare F606


From Nano-Cal :First Order Ghost Strength as a Percentage of Primary Image F225W

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10%

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30%

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80%

180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500

Wavelength (nm)

Tran

smis

sion

Ratio: Measured ghost flux/prime fluxMeasured

Filter Throughput

strong ghost surfaces 4- 2

strong ghost surfaces 4- 3

strong ghost surfaces 3- 2From Models:

200 nm

400 nm

275 nm

1100 nm

F225W

Primary images ghosts

Low level ghosts


First Order Ghost Strength as a Percentage of Primary Image F225W

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Wavelength (nm)

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ns

mis

sio

n

Surfaces (3-2)

Surfaces (4-3)

Surfaces (4-2)

Surfaces (4-1)

meas ghost ratio

meas trans

Surface (3-1)

Surface (2-1)

Note - Surface (4-2)curve overlaps withextended wing of in band transmission

F225

Model Transmission after two reflections. Tocompare models to measured ratio of ghost strength to in-band transmission (black curve with open circles), scale surface curves by transmission (wfc3 + filter + ota + stimulus) at the wavelength. Models do not yet produce as higha ghost transmission ecause of complexities but they indicate which surfaces are most responsible.

Spectral Modeling of Ghosts (D. Kubalak)Spectral Modeling of Ghosts (D. Kubalak)

Ghost spectral modeling- D. Kubalak


Phase Retrieval and Spectral Ghost ModelsPhase Retrieval and Spectral Ghost Models Flight FilterFlight Filter

Phase Retrieval from Focus Sweeps(R. Telfer)

Strange Morphology combination of Astigmatism, overall curvature, local surface ripples


Two-surface reflection modeling indicates the metal blocker is the likely origin of the ghost behavior. Vendors also say that the metal coating is the least “controllable”.

The observed wavelength dependence is understood. Red and Blue near-band wings are not as steep as desired. This excess light occurs at the wavelengths where ghosts could be produced by the air-gap construction. Model ghost fluxes (10-12%) are comparable to measured in white light.

Phase Retrieval reveals ghost images are astigmatic for 218W and 225W, that the coatings are tilted w/r to one another, and filter has a slow, slight curvature possibly consistent with a shrinkage/distortion at the spacer/metal blocker interface.

None of these issues have any effect on the transmitted beam and throughput – both were excellent.

Air-Gap Ghost Mechanisms


Status Filter-Ghost Mitigation Plan

1. Adopt a 3-option approach for Air-Gaps:

Barr to proto-type new F218, 225, (and 300X) filters – single substrate

IPT tested image quality using special lab setup – flightSpare filters to see if they exhibit less ghosting.

IPT is investigating a wedge fix – original design butwith increased wedge to deflect reflected light;

IPT is investigating dual-wheel air gap – achieved wedge by stacked-SOFA wheel approach;requires two coated substrates and loss of a filter(s).

2. Mechanism for F606w (laminated) ghosts is being discussed with OMEGA.

Barr sent thin prototype single substrate – testing in the GSFC – only one ghost present, white light 0.6%

F218 and F225 spares same problem.F606 spare exhibits similar type ghosts butgreatly reduced ghost amplitude (~0.03%)

Modeling shows you cannot tilt filter enough and still stay with bounds of the filter housing..

By “tilting” the spare air-gap, we can determinehow much relative tilt of the two substratesis needed to move the ghosts out of the fov.Data taken last night.

OMEGA is devising a new design.

STATUSPLAN


Off-axisParabola

Filter CCD

Fiber

F/31Beam

Castle CartCastle Cart

DoubleMonochrometer

•UV Sensitive CCD.

•Cover Structure for uniform/dark background.

•Mechanical stage mount for filters.

•Automated Castle and CCD data take system.

•Semi-Automated data reduction and analysis.

GSFC Lab Testing Facility

Goals – last few weeks: 1) Prove that the GSFC Lab Test setup accurately simulates the WFC3, i.e., measurements are true representations of the filter imaging quality, and 2) Measure the flight spares.

Optics Team: R. Telfer, R. Boucarut, D. Kubalak, B. Eichhorn, J. Kirk, B. GreeleyScience IPT: O. Lupie, S. Baggett, B. Hilbert, T. Brown, G. Hartig

presents F31 light beamto the filters as they wouldsee in the WFC3+OTA


SPARE F225Cohu Video CCD,200 micron fiber

FLIGHT F2255 micron fiber,WFC3

10%

0.5%

Saturated prime

10%

Saturated prime

(sum ghosts=15%)

UV00

UV14

Lab Measurements of Spare F225W

Note – rotation and stretch are different.

SPARE F225SBIG CCD,10 micron fiber,

UV00UV14

Saturated prime

9%

2%

0.5%

Relative positions and fluxes of ghosts in the spares are comparable to those in the flight similar mechanisms.


Example Monochromatic Results for Spare F225W

220nm

Spare F225, SBIG-CCD, 200 micron fiber, 13nm bandpass, double UVIS, ,with ND1 (removed in later imaging).

240nm 260nm 280nm

300 nm 320 nm 340 nm

Figure from S.Baggett


Ran many tests to establish sensitivity to ghosts, setup alignment accuracy, and experimented with several different filter orientations: rotation, back to front, tilts, translation, wedge orientation and detector tilts.

nominal

-1d

+1d

-2d

+2d

Establish Setup Sensitivity and RepeatabilityEstablish Setup Sensitivity and Repeatability

Rotate Filter a few degrees from nominal and compareGhost morphology

Xenon Lamp, 10 mic Fiber

Spare F225W


Primary, Secondary ghosts emerge from behind the primary andeach other when large translations or rotations of the filter are introduced:ie different locations on filter and differing field angles.

center

+0.5 in

-0.5 in

+1.0 in

-1.0 in

v. Large tilt –30 deg to corner

saturated unsaturated saturated unsaturated

center - shows repeatability

Establish Setup Sensitivity and RepeatabilityEstablish Setup Sensitivity and RepeatabilityAlso Helps modelers to see all the ghostsAlso Helps modelers to see all the ghosts

Translating the filter

Xenon Lamp, 10 mic Fiber



Prototype F225 – Single SubstratePrototype F225 – Single Substrate

Prototype Single Substrate – large tilts(Xenon Lamp, 10 micron fiber, CCD SBIG)

nominal -3d -6d

-9d -12d -15d

Prototype thickness is smaller than that of a flight filter. Thicker filters result in ghosts at a larger radial distance from the primary.

But tilting the thin filter, we can see when the ghost emerges and use a simpleModel to derive the ghost position with a thicker filter.

Setup artifact

Ghost 0.6%



"Feb_19 Trial F225W"

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"Wavelength"

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flight 225-302 trans

orig theor

Feb_19 Trial F225W" - OOB Blocking

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ProtoTypeF225FromBarr


Prototype F225 – Single SubstratePrototype F225 – Single Substrate

Ghosts as a function of wavelength

SetupSBIG CCD, 200 mic fiberCastle Modes<250nm double UV250-310 double UVIS310-760 double VIS>760 double IR

Setup artifact

Ghost#1Ghost#2

200nm 225nm 250nm 300nm

350nm 400nm 450nm 500nm

600nm

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750nm

900nm



• 53 of 63 filters exhibit excellent performance, consistent with spec.

• 47 filters < 0.2% ghosts• 6 filters 0.2-0.5% ghosts - multi-substrate - 410M, 689M, 814M - air-gap – 656N, 665N, 673N

• 2 filters 0.7% ghosts: • single substrate+Al blocker - 275W can calibrate• air-gap - 658N

• 2 UV high priority air-gap (with Aluminum blocker) 10-15% ghosts - 218W, 225W unsuitable for flight

• 1 UV air-gap 1% with strange morphology - 300X marginal, tough to calibrate

• 1 3-substr laminated, < 0.5% “point-like” ghosts - 606W most used filter, concern (other filters with very low level “point ghosts”: 625W, 775W, 410M, 467M, 547M, 621M, 689M)

• 1 UV single subst.+Al block, possible surface flaw – 280N serious but low priority filter

• 2 UV Quad filters single substrate, 5% ghosts:– 232N, 243N low priority filters, can calibrate

• Grism – data reduction in work

march 18, 2004tips – olivia lupie1 wfc3 filter testing, modeling, designing ghosts (spurious...

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