COPAG Technology Assessment: UV Photon-Counting Detector Developments

1. COPAG Technology Assessment:UV Photon-Counting Detector Developments That Will Enable Future UV/Optical Missions Christopher Martin California Institute of Technology COPAG Workshop 8 Jan 2012 – AAS Austin

2. Applications for UV Photon Counting Detectors IGM UV high-R absorption Spectroscopy of QSOs, Galaxies UV Imaging Spectroscopy of IGM/CGM UV High Resolution/ Wide-field Imaging HST/COS/StScI UV Imaging Spectroscopy of Galaxies Multi-Object Spectroscopy Of Star Clusters, Galaxies, CGM NRC Roadmap Panel

3. UV/Optical photon-counting detectorsNeed for photon-counting Photon background [ph s-1 pixel-1] Space UV Optical

4. Why UV? Dark UV Sky!

5. Mira

6. UV/Optical photon-counting detectorsNeed for low detector background to be sky-limited Photon background [ph s-1 pixel-1] Space UV Optical 1 ct cm-2 s-1 (f/30, e=0.1) 0.1 ct cm-2 s-1 (f/4, e=0.1)

7. 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/Optical photon-counting detectorsNeed for large formats UV Multi—Object Spectrograph Simulated Image

8. UV photon-counting detectors Need for Quantum Efficiency Improvements

9. 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)

10. Applications for UV Photon-counting DetectorsExample: 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=6  Transformational (Game-changing) Capability

11. (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). 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

12. Measurement  UV Detector Requirements

13. Detector Requirement Definitions

14. 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 GALEX Small Explorer 65 mm diam MCPs have 200+ “detector years” in space including mission to Pluto (estimated existence > 109 yrs) Siegmund, Vallerga et al.

15. 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?

16. EBCCDs/EBCMOS Woodgate, Joseph, Stocke et al.

17. AR-Coated, Delta-Doped L3 Detectors Photon-Counting, High QE, Low Background e2v L3 Technology JPL Delta Doping • 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. Wafer Polish Wafer Thinning Data Flow • JPL Delta Doping technology sensitizes L3 CCDs to the ultraviolet. • A 10X improvement in performance is possible over CsI/CsTe MCP detectors. Storage Area L3 functional diagram UV Photons Serial register Extended serial register (50V) MBE/Delta Doping Amplified data is sent to a photon counting discriminator, eliminating read noise. Image Area Nikzad, Morrissey et al.

18. 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

19. Photon-Counting UV Detector Implementations

20. Technology Matrix

21. Technology Matrix NRC Roadmap Panel Workshop -- Photon-counting detectors