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Calibration Screen Development Calibration Screen Development Calibration Screen Development Calibration Screen Development

Claire CramerClaire Cramer

Brian StalderBrian Stalder

Gautham NarayanGautham Narayan

Christopher StubbsChristopher Stubbs

Department of Physics Department of Physics

Harvard UniversityHarvard University

Claire CramerClaire Cramer

Brian StalderBrian Stalder

Gautham NarayanGautham Narayan

Christopher StubbsChristopher Stubbs

Department of Physics Department of Physics

Harvard UniversityHarvard University

                                                 

Keith LykkeKeith Lykke

Steve BrownSteve Brown

Allan SmithAllan Smith

NISTNIST

John TonryJohn Tonry

Jeff MorganJeff Morgan

Ken ChambersKen Chambers

PanSTARRSPanSTARRS

Keith LykkeKeith Lykke

Steve BrownSteve Brown

Allan SmithAllan Smith

NISTNIST

John TonryJohn Tonry

Jeff MorganJeff Morgan

Ken ChambersKen Chambers

PanSTARRSPanSTARRS

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OverviewOverviewOverviewOverview

• ObjectivesObjectives

• StatusStatus

• ChallengesChallenges

• PlansPlans

• ObjectivesObjectives

• StatusStatus

• ChallengesChallenges

• PlansPlans

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ObjectivesObjectivesObjectivesObjectives

• We hope to achieve unprecedented We hope to achieve unprecedented precisionprecision in LSST in LSST

photometry.photometry.

• This requires knowingThis requires knowing• Relative sensitivity of apparatus vs. wavelength

• Transmission of atmosphere.

• Our plan is to use a NIST-calibrated photodiode as the Our plan is to use a NIST-calibrated photodiode as the

primary flux sensitivity reference. primary flux sensitivity reference.

• We will use full-aperture illumination of the system to map out We will use full-aperture illumination of the system to map out

each pixel’s response vs. wavelength, for each LSST filter. each pixel’s response vs. wavelength, for each LSST filter.

• (Measurement of atmospheric transmission is a distinct issue, (Measurement of atmospheric transmission is a distinct issue,

for a later conversation)for a later conversation)

• We hope to achieve unprecedented We hope to achieve unprecedented precisionprecision in LSST in LSST

photometry.photometry.

• This requires knowingThis requires knowing• Relative sensitivity of apparatus vs. wavelength

• Transmission of atmosphere.

• Our plan is to use a NIST-calibrated photodiode as the Our plan is to use a NIST-calibrated photodiode as the

primary flux sensitivity reference. primary flux sensitivity reference.

• We will use full-aperture illumination of the system to map out We will use full-aperture illumination of the system to map out

each pixel’s response vs. wavelength, for each LSST filter. each pixel’s response vs. wavelength, for each LSST filter.

• (Measurement of atmospheric transmission is a distinct issue, (Measurement of atmospheric transmission is a distinct issue,

for a later conversation)for a later conversation)

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Detectors are better characterized Detectors are better characterized than than anyany celestial source! celestial source!

Detectors are better characterized Detectors are better characterized than than anyany celestial source! celestial source!

nm

QE

Spectrum of Vega NIST photodiode QE Spectrum of Vega NIST photodiode QE

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Basic ConceptBasic Concept

Back-illuminated diffuserBack-illuminated diffuser

Monitoring photodiodeMonitoring photodiode

LSST apertureLSST aperture

focal planefocal plane

Basic ConceptBasic Concept

Back-illuminated diffuserBack-illuminated diffuser

Monitoring photodiodeMonitoring photodiode

LSST apertureLSST aperture

focal planefocal plane

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Demonstration of the concept at CTIODemonstration of the concept at CTIODemonstration of the concept at CTIODemonstration of the concept at CTIO

• Measured full system transmission Measured full system transmission using a tunable laser and NIST using a tunable laser and NIST diode. diode.

• This was not a permanent This was not a permanent installation. installation.

• Measured full system transmission Measured full system transmission using a tunable laser and NIST using a tunable laser and NIST diode. diode.

• This was not a permanent This was not a permanent installation. installation.

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Tunable laser (400 nm - 2 microns) Tunable laser (400 nm - 2 microns)

from Opotekfrom Opotek Tunable laser (400 nm - 2 microns) Tunable laser (400 nm - 2 microns)

from Opotekfrom Opotek

Second harmonic Second harmonic (532 nm) generator(532 nm) generator

Mixer (to 355 nm) Mixer (to 355 nm)

1.064 micron 1.064 micron NdYAG pulsed NdYAG pulsed

pump laserpump laser

Tunable Tunable downconverterdownconverter

Second harmonic Second harmonic (532 nm) generator(532 nm) generator

Mixer (to 355 nm) Mixer (to 355 nm)

1.064 micron 1.064 micron NdYAG pulsed NdYAG pulsed

pump laserpump laser

Tunable Tunable downconverterdownconverter

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A/D converter module

Photdiode preamp

USB extender

Integrator electronics

Calibrated photodiode

Beam launch optics

Optical Fiber

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Preliminary results from this Preliminary results from this approachapproachPreliminary results from this Preliminary results from this approachapproach

Relative system Relative system response vs. response vs.

wavelength for wavelength for CTIO Mosaic CTIO Mosaic

imagerimager

100 x 100 pixel 100 x 100 pixel block averageblock average

Multiple points at Multiple points at 800 nm show 800 nm show

repeatability of repeatability of 0.4% 0.4%

Relative system Relative system response vs. response vs.

wavelength for wavelength for CTIO Mosaic CTIO Mosaic

imagerimager

100 x 100 pixel 100 x 100 pixel block averageblock average

Multiple points at Multiple points at 800 nm show 800 nm show

repeatability of repeatability of 0.4% 0.4%

, nm, nm

TT

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Actual data from CTIO R Band Actual data from CTIO R Band Colored Glass FilterColored Glass Filter

Actual data from CTIO R Band Actual data from CTIO R Band Colored Glass FilterColored Glass Filter

System throughput System throughput Filtered/blank=filter onlyFiltered/blank=filter only

System throughput System throughput Filtered/blank=filter onlyFiltered/blank=filter only

, nm, nm , nm, nm

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950 nm950 nm950 nm950 nm

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960 nm960 nm960 nm960 nm

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970 nm970 nm970 nm970 nm

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980 nm980 nm980 nm980 nm

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990 nm990 nm990 nm990 nm

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1000 nm1000 nm1000 nm1000 nm

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1010 nm1010 nm1010 nm1010 nm

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1020 nm1020 nm1020 nm1020 nm

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Position Dependence in ResponsePosition Dependence in ResponsePosition Dependence in ResponsePosition Dependence in Response

780 nm780 nm

890 nm890 nm

780 nm780 nm

890 nm890 nm

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This approach requiresThis approach requiresThis approach requiresThis approach requires

1.1. Photodiode monitor & circuitPhotodiode monitor & circuit

2.2. Tunable light source with adequate intensityTunable light source with adequate intensity

3.3. Uniform radiance screen, to ~10%. An adjustable Uniform radiance screen, to ~10%. An adjustable

source of illumination across the screen would be source of illumination across the screen would be

nice!nice!

4.4. Calibration pipeline that exploits these data.Calibration pipeline that exploits these data.

5.5. Dark dome (or at least uniform illumination) Dark dome (or at least uniform illumination)

1.1. Photodiode monitor & circuitPhotodiode monitor & circuit

2.2. Tunable light source with adequate intensityTunable light source with adequate intensity

3.3. Uniform radiance screen, to ~10%. An adjustable Uniform radiance screen, to ~10%. An adjustable

source of illumination across the screen would be source of illumination across the screen would be

nice!nice!

4.4. Calibration pipeline that exploits these data.Calibration pipeline that exploits these data.

5.5. Dark dome (or at least uniform illumination) Dark dome (or at least uniform illumination)

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We are building a DLP-driven We are building a DLP-driven flatfield screenflatfield screen

We are building a DLP-driven We are building a DLP-driven flatfield screenflatfield screen

Hacked DLP digital projector, optical fiberHacked DLP digital projector, optical fiber

Transmissive screenTransmissive screen

Diverging mirrorsDiverging mirrors

Tunable sourceTunable source

We can currently generate a 2m dia spot in ~26 inches depthWe can currently generate a 2m dia spot in ~26 inches depthI expect we can fill LSST screen uniformly with 2m depth I expect we can fill LSST screen uniformly with 2m depth

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Transferring uniform radianceTransferring uniform radianceTransferring uniform radianceTransferring uniform radiance

Flat, by def. Non-uniform Iteratively flattenedFlat, by def. Non-uniform Iteratively flattened

reciprocalreciprocal

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ChallengesChallengesChallengesChallenges

• We can add a collimator, to restrict angles of We can add a collimator, to restrict angles of

emission to the FOV of camera, but then uniformity emission to the FOV of camera, but then uniformity

measurement is difficult. measurement is difficult.

• Need optimized optical surfaces for reflectors to Need optimized optical surfaces for reflectors to

project decent spot in minimal standoff distance. project decent spot in minimal standoff distance.

• Tunable light sources below 400nm are difficult.Tunable light sources below 400nm are difficult.

• Don’t yet know requisite cadence of filter Don’t yet know requisite cadence of filter

transmission measurements. transmission measurements.

• Plan to ship v1.0 to PanSTARRS in May.Plan to ship v1.0 to PanSTARRS in May.

• We can add a collimator, to restrict angles of We can add a collimator, to restrict angles of

emission to the FOV of camera, but then uniformity emission to the FOV of camera, but then uniformity

measurement is difficult. measurement is difficult.

• Need optimized optical surfaces for reflectors to Need optimized optical surfaces for reflectors to

project decent spot in minimal standoff distance. project decent spot in minimal standoff distance.

• Tunable light sources below 400nm are difficult.Tunable light sources below 400nm are difficult.

• Don’t yet know requisite cadence of filter Don’t yet know requisite cadence of filter

transmission measurements. transmission measurements.

• Plan to ship v1.0 to PanSTARRS in May.Plan to ship v1.0 to PanSTARRS in May.

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Selected ReferencesSelected ReferencesSelected ReferencesSelected References

• Stubbs & Tonry “Stubbs & Tonry “Toward 1% Photometry: End-to-End Toward 1% Photometry: End-to-End Calibration of Astronomical Telescopes and Detectors” Calibration of Astronomical Telescopes and Detectors” ApJ 646, 1436 (2006)

• Stubbs et al. “Stubbs et al. “Preliminary Results from Detector-Based Preliminary Results from Detector-Based Throughput Calibration of the CTIO Mosaic Imager and Blanco Throughput Calibration of the CTIO Mosaic Imager and Blanco Telescope Using a Tunable Laser”Telescope Using a Tunable Laser” astro-ph/0609260 (2006) astro-ph/0609260 (2006)

• Stubbs et al, “Stubbs et al, “Toward More Precise Survey Photometry for Toward More Precise Survey Photometry for PanSTARRS and LSST: Measuring Directly the Optical PanSTARRS and LSST: Measuring Directly the Optical Transmission Spectrum of the Atmosphere” Transmission Spectrum of the Atmosphere” PASP 119, 1163 PASP 119, 1163 (2007)(2007)

• Technical Memo on Screen Design Considerations. C. Stubbs Technical Memo on Screen Design Considerations. C. Stubbs Dev 2007. Dev 2007.

• Stubbs & Tonry “Stubbs & Tonry “Toward 1% Photometry: End-to-End Toward 1% Photometry: End-to-End Calibration of Astronomical Telescopes and Detectors” Calibration of Astronomical Telescopes and Detectors” ApJ 646, 1436 (2006)

• Stubbs et al. “Stubbs et al. “Preliminary Results from Detector-Based Preliminary Results from Detector-Based Throughput Calibration of the CTIO Mosaic Imager and Blanco Throughput Calibration of the CTIO Mosaic Imager and Blanco Telescope Using a Tunable Laser”Telescope Using a Tunable Laser” astro-ph/0609260 (2006) astro-ph/0609260 (2006)

• Stubbs et al, “Stubbs et al, “Toward More Precise Survey Photometry for Toward More Precise Survey Photometry for PanSTARRS and LSST: Measuring Directly the Optical PanSTARRS and LSST: Measuring Directly the Optical Transmission Spectrum of the Atmosphere” Transmission Spectrum of the Atmosphere” PASP 119, 1163 PASP 119, 1163 (2007)(2007)

• Technical Memo on Screen Design Considerations. C. Stubbs Technical Memo on Screen Design Considerations. C. Stubbs Dev 2007. Dev 2007.