COPAG Technology Assessment:UV Photon-Counting Detector Developments That Will Enable Future UV/Optical Missions

Christopher MartinCalifornia Institute of Technology

COPAG Workshop 8 Jan 2012 – AAS Austin

Applications for UV Photon Counting Detectors

IGM UV high-R absorption Spectroscopy of QSOs, Galaxies

Multi-Object SpectroscopyOf Star Clusters, Galaxies, CGM

HST/COS/StScI

UV High Resolution/Wide-field Imaging

UV ImagingSpectroscopy of IGM/CGM

UV ImagingSpectroscopy of Galaxies

NRC Roadmap Panel2

3

UV/Optical photon-counting detectorsNeed for photon-counting

Space UV

Optical

Photon background [ph s-1 pixel-1]

Why UV? Dark UV Sky!

4

Mira

5

6

UV/Optical photon-counting detectorsNeed for low detector background to be sky-limited

Space UV

Optical

Photon background [ph s-1 pixel-1]

1 ct cm-2 s-1 (f/30, e=0.1)

0.1 ct cm-2 s-1 (f/4, e=0.1)

UV/Optical photon-counting detectorsNeed for large formats

Pixels Format

Wide field imaging 10,000 * 10,000 ~ 108 10’s cm x 10’s cmCurved focal plane?

High Resolution Spectroscopy (multi-object?)

# ~ R*3*MUX*2 #~ 100,000 * 3 * 100 * 2 #~ 108

10’s cm longCurved focal plane?

Multi-object spectroscopy # ~ R*3*MUX*2#~ 3,000 * 3 * 1000 * 2 #~2*107

10’s cm x 10’s cmCurved focal plane?

Imaging Spectroscopy #~(FOV/Q)2R*2*2#~3*107

10 cm x 10 cmCurved focal plane?

HST-COS far-ultraviolet detector showing the two abutting microchannel plate detector segments (each 85 x 10 mm) curved to the focal plane of the spectrograph.

UV Multi—Object Spectrograph Simulated Image

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UV photon-counting detectors Need for Quantum Efficiency Improvements70

60

50

40

30

20

10

0

QE

(%)

300275250225200175150125

Wavelength (nm)

GALEX NUV

MgF213 nm

Al2O316 nm

Al2O323 nm

HfO223 nm

GALEX FUV

Bare

COS FUV MCP

1216 Å ~34%

1300 Å ~30%

1400 Å ~23%

1500 Å ~20%

1600 Å ~13%

1750 Å ~ 10%

COS NUV MAMA

2000 Å ~10%

2500 Å ~9%

3000 Å ~4%

UV photon-counting detectors Need for Quantum Efficiency Improvements

• The throughput of optical systems at ultraviolet wavelengths has considerable headroom for growth.

• Even Optical/IR designs can be improved via multiplexing.• Technology investments can be traded against aperture size.

• Investments would benefit all mission sizes (SMEX MIDEX, Probe-Class, Flagship)

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Applications for UV Photon-counting Detectors

Example: Cosmic Web Mapping: SNR Calculation• SNR w/ MCP, 10% QE, 1 ct/cm2/sec

– 106 sec, 1600Å, 200LU, 10” x 10”, S/N=1.4• SNR w/ 2 e- UV CCD

– 106 sec, 1600Å, 200LU, 10” x 10”, S/N=0.4• SNR w/ photon-counting detector, 70% QE

– 106 sec, 1600Å, 200LU, 10” x 10”, S/N=6MCP UV CCD

(2 e-)UV PC-Det

(0 e-)Telescope Diameter

2.3 8 m 0.5 m

Mission Cost 1.2B 9B 0.1B Transformational (Game-changing) Capability

UV photon-counting detectors Implementation Issues

• Sealed tubes are difficult to fabricate• Scalability, Modularity• Robustness, Stability, QE Hysteresis• Radiation hardness

– Charge transfer efficiency primarily an issue for large CCDs in space– p-channel vs. n-channel can help– CMOS (or APS) devices hold great promise but currently have higher read noise

and lower QE than conventional CCDs; need development• Operation at “room” temperature

– Contamination of UV optics and detectors is a concern at cryogenic temperatures• Flatfields

(Left) HST-COS flat field image of a 10 x 13 mm area of the far-ultraviolet MCP detector. The fiber bundles imprint an obvious fixed-pattern noise features in the image. (Right) A new glass process MCP flat field for a similar image area, demonstrating the absence of fixed-pattern noise (Siegmund et al. 2007).

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Measurement UV Detector Requirements

UV Detector Property

UV High Resolution/High

Contrast Imaging

UV Wide Field Imaging

UV High Resolution

Spectroscopy

UV Multi-Object

Spectroscopy

UV Integral Field

Spectroscopy

Current Performance

QE Moderate Moderate High-Very High High High-

Very HighLow-Very

LowFormat: Number of Pixels

Very High Very High High-Very High

High-Very High

High-Very High High

Photon-counting XX X XXX XX XXX YES

Equivalent background Low Moderate Very Low Low-Very

Low Very Low Moderate

Dynamic Range High High Moderate Moderate Moderate Moderate

Radiation Tolerance Moderate Moderate Moderate Moderate Moderate High

Time Resolution Low Low Low Low Low High

Out of Band Rejection High High Moderate Moderate Moderate High

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Detector Requirement DefinitionsUV DETECTORPROPERTY Very Low Low Moderate / X High /

XX Very High / XXX

QE >5% >15% >30% >50% >70%

Format: Number of Pixels

100 x 100104

300 x 300105

103 X 103

106(3000)2

107(10,000)2

108

Photon-counting Not important Important Very Important Critical

Equivalent background [ct cm-2 s-1]

0.01 0.1 1.0 10 100

Dynamic Range [ct/s] 10-3:100 10-3:101 10-3:102 10-3:103 10-3:105

Radiation Tolerance 1 kRad 10 kRad 100 kRad 1000 kRad

Time Resolution None 1000 s 1 s 1 msec 1 usec

Out of Band Rejection [including

1 10-1 10-2 10-3 10-4

MCP Detectors have been the Workhorse of UV Astronomy (with Planetary,

Heliophysics Apps) COS FUV for Hubble (200 x 10 mm windowless)

18 mm Optical Tube

GALEXSmall Explorer65 mm diam MCPs have 200+ “detector

years” in space including mission to Pluto

(estimated existence > 109 yrs)Siegmund, Vallerga et al.

Borosilicate Microchannel Plate Detectors with GaN Photocathodes

40 µm pore borosilicate micro-capillary substrate with 83% open area

Borosilicate MCPs with ALD coated secondary electron emission coating-- Deterministic manufacture-- Uniform-- Robust, Rad Hard-- Operate at lower HV-- Very low background

GaN Photocathodes-- Extend good QE of CsI, KBr (>30%) to 200-250 nm-- Issue: what is Quantum Yield?

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EBCCDs/EBCMOS

Woodgate, Joseph, Stocke et al.

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AR-Coated, Delta-Doped L3 Detectors Photon-Counting, High QE, Low

Background

•JPL Delta Doping technology sensitizes L3 CCDs to the ultraviolet. •A 10X improvement in performance is possible over CsI/CsTe MCP detectors.

• New technology from e2v enables high QE CCD imaging and zero read noise photon counting. •A Low Light Level (L3) extended serial register operating at elevated voltage (~50V) amplifies signals well above the level of the read noise.Image

AreaStorage

Area

Data Flow

Serial registerExtended serial register (50V)

Amplified data is sent to a photon countingdiscriminator, eliminating read noise.

UV PhotonsL3 functional diagram

e2v L3 Technology JPL Delta Doping

Wafer Polish

Wafer Thinning

MBE/Delta Doping

70

60

50

40

30

20

10

0

QE

(%)

300275250225200175150125

Wavelength (nm)

GALEX NUV

MgF213 nm

Al2O316 nm

Al2O323 nm

HfO223 nm

GALEX FUV

Bare

Nikzad, Morrissey et al.

AR-Coated, Delta-Doped L3 Detectors Red Leak is Manageable for UV spectroscopy

• Spectroscopy – Red Leak not a problem– Dominant red leak = scattering– Scattering ~ λ-3

• 1 power width factor, 2 powers total energy scattered)

– With no filtering: • (Red leak) ~ 5% (UV background)

– With 1 band-selecting Reflective Dielectric Multilayer

• (Red leak) << 1% (UV background)

• Dynamic range > 104 (~10 magnitudes)

• Reddest objects are FUV-r~7-8 magnitudes

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Photon-Counting UV Detector Implementations

UV DETECTORPROPERTY [Projected, 2020]

Conventional MCPs+CsI/CsTe

Borosilcate ALD MCPs+GaN EBCCDs+GaN

AR-Coated, Delta-Doped

EMCCDs

GaN Solid-State AvalancheDetectors

QE 100 | 150 | 200 nm Low25% | 15% | 8%

High>25%

High>30%

Very High>50-70%

High>30%

Format: Number of Pixels

High107

Very High107-8

High106-7

Very High107-8

Very Low104-5

Equivalent background [ct cm-2 s-1]

Medium0.5

Low0.1 Low Low-Very Low

0.01-0.1Extremely High

>1010

Dynamic Range [ct/s] Moderate High Moderate High Moderate

Radiation Tolerance High High High-Very High Medium-High High-Very High

Time Resolution <1 msec <1 msec <1 msec 1-1000 sec <1 msec

Out of Band Rejection Very High High High Medium (spec) High

Leverage Very High High Moderate High High

TRL [2011] 9 2-32-3

(IMAPS version=9)

3-4 1-2

Implementation Issues HV, sealed tubes HV, sealed tubes HV, sealed tubes Cooling, Red leak

Lifetime, background

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Technology MatrixName of technology High QE, large format photon-counting UV large-format detectors

Brief description (1024) Future NASA UV missions, particularly those devoted to spectroscopy, require high quantum efficiency (>50%), low noise (<1e-7 ct/pixel/s), large-format (>4k x \4k) photon-counting detectors for operation at 100-400nm or broader

Goals and Objectives The goal is to produce large-format, high QE, low-noise, photon-counting UV-sensitive detectors routinely that can be employed in a variety of explorer, medium, and strategic missions.

TRL Silicon-CCD detectors are TRL4. MCPs with GaN are TRL2-3. GaN APDs are TRL1.

Tipping point (100 words or less)

TRL6 with Si-CCD and MCP/GaN detectors can be achieved in ≈2 years with modest funding investment; in APDs later.

NASA capability (100 words of less)

NASA is partnering with industry to produce these detectors.

Benefit High performance detectors can increase the science impact of missions by 10-1000. 2010 Astro Decadal survey noted importance of technology development for a future 4-m class UV/optical mission for spectroscopy and imaging

NASA Needs Current UV detectors obtain ~5-20% QE.. The science impact of cost-constrained, aperture-constrained future missions is dramatically improved by reaching near-perfect detector performance. Benefits will also accrue to Planetary, Heliospheric, and Earth missions in the UV band.

Non-NASA but aerospace needs

High performance UV detectors can have numerous aerospace applications, remote-sensing, situational awareness, etc.

Non-aerospace needs High performance UV detectors may have applications in bio and medical imaging.

Technical risk Technical risk of Si-CCD and MCP detectors is low-moderate because of prior investments and existing infrastructure. .

Sequencing/timing

Should come as early as possible since mission definition and capabilities are built around detector performance. There is a clear plan to achieve this technology. Users identified.

Time and effort 5 year collaboration between NASA, university groups, and industry.

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Technology MatrixName of technology

High QE, large format photon-counting UV large-format detectors

Priority 1 – Detectors are at the heart of every instrument. Detector performance shortfalls can only be made up with high cost increases in aperture.

Roadmap

1) 2011-2014: Investigate 2-4 technological approaches. Goal is demonstration of high QE, low/moderate noise, and moderate/high (scaleable) pixel counts

2) 2015: Downselect to 2 promising technologies that have reached TRL3-4.

3) 2015-2019: Invest in 2 technologies that provide best capabilities for UV imaging and UV spectroscopy. Scale to high/very high pixel counts. Develop low power versions of required electronics.

3/29/11 -- C. Martin NRC Roadmap Panel Workshop -- Photon-counting detectors