1. LLNL AO talk - Aug. 17, 2004 John Vallerga, Jason McPhate, Anton Tremsin and Oswald Siegmund Space Sciences Laboratory, University of California, Berkeley Bettina Mikulec and Allan Clark University of Geneva A noiseless 512 x 512 detector for AO with kHz frame rates

2. LLNL AO talk - Aug. 17, 2004 Future WFS Requirements* High (~80%) optical QE Lots of pixels - eventually 512x512 Very low readout noise (< 3 e - ) kHz frame rates The last three are not simultaneously achievable with the current generation of CCDs *Angel et al “A Road Map for the Development of Astronomical AO”

3. LLNL AO talk - Aug. 17, 2004 Imaging, Photon Counting Detectors Photocathode converts photon to electron MCP(s) amplify electron by 10 4 to 10 8 Rear field accelerates electrons to anode Patterned anode measures charge centroid

4. LLNL AO talk - Aug. 17, 2004 Why would you want one? No readout noise penalty –Use as many pixels as you wish Continuous temporal sampling to ~ nsecs –Choose integration period(s) after the fact or on the fly Other advantages –Large area, curved focal planes –Cosmic ray = 1 count –LN 2 not required –Low dark current (0.16 attoamps cm -2 )

5. LLNL AO talk - Aug. 17, 2004 Spatial Resolution 12 µm pore glass MCPs7 µm pore glass MCPs Cross Strip readout of Glass MCPs

6. LLNL AO talk - Aug. 17, 2004 MCP Detectors at SSL Berkeley COS FUV for Hubble (200 x 10 mm windowless) 25 mm Optical Tube GALEX 68 mm NUV Tube (in orbit)

7. LLNL AO talk - Aug. 17, 2004 GaAs Photocathodes (GenIII) Developed for night vision tubes Slight cooling required (10 4 cps at room temp) Only fabricated in USA and Japan

8. LLNL AO talk - Aug. 17, 2004 GaN UV Photocathodes, 1000- 4000Å

9. LLNL AO talk - Aug. 17, 2004 Advantages of multi-pixel sampling of Shack Hartman spots  Linear response off-null  Insensitive to input width  More sensitive to readout noise 2 x 2 5 x 5

10. LLNL AO talk - Aug. 17, 2004 Wavefront Sensor Event Rates 5000 centroids Kilohertz feedback rates (atmospheric timescale) 1000 detected events per spot for sub-pixel centroiding  5000 x 1000 x 1000 = 5 Gigahertz counting rate! Requires integrating detector

11. LLNL AO talk - Aug. 17, 2004 Our AO detector concept An optical imaging tube using: –GaAs photocathode –Microchannel plate to amplify a single photoelectron by 10 4 –ASIC to count these events per pixel

12. LLNL AO talk - Aug. 17, 2004 Medipix2 ASIC Readout  Pixellated readout for x and gamma ray semiconductor sensors (Si, GaAs, CdTe etc)  Developed at CERN for Medipix collaboration  55 µm pixel @ 256x256 (buttable to 512 x 512).  Pixel level amp, discriminator, gate & counter.  Counts integrated at pixel No charge transfer! 14mm 16mm Applications: Mammography, dental radiography, dynamic autoradiography, gamma imaging, neutron imaging, angiography, xray diffraction, dynamic defectoscopy, etc.

13. LLNL AO talk - Aug. 17, 2004 Single Medipix2 pixel Each 55µm Pixel has ~ 500 transistors using 0.25µm CMOS technology

14. LLNL AO talk - Aug. 17, 2004 Readout Architecture 3328 bit Pixel Column 0 3328 bit Pixel Column 255 3328 bit Pixel Column 1 256 bit fast shift register 32 bit CMOS outputLVDS out Pixel values are digital (13 bit) Bits are shifted into fast shift register Choice of serial or 32 bit parallel output Maximum designed bandwidth is 100MHz Corresponds to 266µs frame readout

15. LLNL AO talk - Aug. 17, 2004 “Built-in” Electronic Shutter Enables/Disables counter Timing accuracy to 10 ns Uniform across Medipix Multiple cycles per frame No lifetime issues External input - can be phased to laser What is the best strategy to remove/measure parallax?

16. LLNL AO talk - Aug. 17, 2004 First test detector Demountable detector Simple lab vacuum, no photocathode UV sensitive

17. LLNL AO talk - Aug. 17, 2004 Initial Results It Works! First light! Lower gain, higher rear field

18. LLNL AO talk - Aug. 17, 2004 Photon counting movie

19. LLNL AO talk - Aug. 17, 2004 Spatial Resolution 100 µs1 s Group 3-2 visible 9 lp/mm = 55µm (Nyquist limit)

20. LLNL AO talk - Aug. 17, 2004 Optimizing charge cloud size Medipix2 “non-photometric” # pixels per photon dependent on: MCP-anode gap Rear field voltage MCP gain and threshold of Medipix pixel amp

21. LLNL AO talk - Aug. 17, 2004 MCP event spot area

22. LLNL AO talk - Aug. 17, 2004 MCP charge cloud size

23. LLNL AO talk - Aug. 17, 2004 Modeling Optimum sampling Input spot size, charge cloud size Generate N photons per frame Calculate spot centroid Repeat M times and plot error distribution

24. LLNL AO talk - Aug. 17, 2004 Spot size vs gain Pinhole grid mask (0.5 x 0.5 mm) Gain: 200,000 Rear Field: 1600V Threshold: 3 ke - Gap: 500µm

25. LLNL AO talk - Aug. 17, 2004 Spot size vs gain Pinhole grid mask (0.5 x 0.5 mm) Gain: 20,000 Rear Field: 1600V Threshold: 3 ke - Gap: 500µm

26. LLNL AO talk - Aug. 17, 2004 Example of sub pixel resolution 9 lp/mm Calculate centroids of each event Accumulate event x,y list 2-d histogram on finer pitch

27. LLNL AO talk - Aug. 17, 2004 Calculate centroids of each event Accumulate event x,y list 2-d histogram on finer pitch 16 lp/mm Example of sub pixel resolution

28. LLNL AO talk - Aug. 17, 2004 Flat Field 1200 cts/bin - 500Mcps MCP deadspots Hexagonal multifiber boundaries

29. LLNL AO talk - Aug. 17, 2004 Flat Field (cont) Histogram of Ratio consistent with counting statistics (2% rms) Ratio Flat1/Flat2

30. LLNL AO talk - Aug. 17, 2004 Future Work (3 yr. NOAO grant) Optimize MCP-Medipix2 interface design Design and build tube with Medipix2 and GaAs Develop parallel readout with European collaborators Develop FPGA to reduce output bandwidth –5 million centroids/s vs. 262 million pixels/s. Test at AO laboratory at CFAO, U.C. Santa Cruz Test at telescope

31. LLNL AO talk - Aug. 17, 2004 Vacuum Tube Design

32. LLNL AO talk - Aug. 17, 2004 Vacuum Tube Design

33. LLNL AO talk - Aug. 17, 2004 Vacuum Tube Design

34. LLNL AO talk - Aug. 17, 2004 Vacuum Tube Design

35. LLNL AO talk - Aug. 17, 2004 Issues/Concerns QE ! Throughput –global –local Detector Lifetime Downstream interface Cost

36. LLNL AO talk - Aug. 17, 2004 Acknowledgements Univ. of Barcelona University of Cagliari CEA CERN University of Freiburg University of Glasgow Czech Academy of Sciences Mid-Sweden University University of Napoli NIKHEF University of Pisa University of Auvergne Medical Research Council Czech Technical University ESRF University of Erlangen-Nurnberg Thanks to the Medipix Collaboration: This work was funded by an AODP grant managed by NOAO and funded by NSF

37. LLNL AO talk - Aug. 17, 2004 Soft X-Ray Photocathodes

38. LLNL AO talk - Aug. 17, 2004 EUV and FUV