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A noiseless 512 x 512 detector for AO with kHz frame rates

A noiseless 512 x 512 detector for AO with kHz frame rates. John Vallerga, Jason McPhate, Anton Tremsin and Oswald Siegmund Space Sciences Laboratory, University of California, Berkeley Bettina Mikulec and Allan Clark University of Geneva. Future WFS Requirements*. High (~80%) optical QE

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A noiseless 512 x 512 detector for AO with kHz frame rates

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

  2. 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. Imaging, Photon Counting Detectors • Detects individual quanta of light via photoelectric effect • Microchannel plate amplifies single electron to large charge cloud • Signal per photon >> noise • Readout gives X,Y of every event • Time of every event also available

  4. Microchannel Plates 2 µm pores on 3 µm centers (Burle Industries)

  5. MCP Detectors at Berkeley COS FUV for Hubble (2004,2005,???) 10 mm 25 mm Optical Tube 400pxl 85 mm 14000 pxl GALEX NUV Tube (in orbit) 68 mm

  6. GaAs Photocathodes (GenIII) • Developed for night vision tubes • Slight cooling required (104 cps at room temp) • Only fabricated in USA and Japan

  7. Advantages of multi-pixel sampling of Shack Hartman spots 5 x 5 2 x 2 • Linear response off-null • Insensitive to input width • More sensitive to readout noise

  8. Wavefront Sensor Photon Rate • Future large telescopes need > 5000 actuators • Kilohertz feedback rates • 1000 detected events per spot for sub-pixel centroiding 5000 x 1000 x 1000 • 5 Gigahertz counting rate! • 104 time faster than existing photon counting imagers • Requires integrating readout

  9. Our detector concept An optical imaging tube using: • GaAs photocathode • Microchannel plate to amplify a single photoelectron by 104 • ASIC to count these events per pixel

  10. 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.

  11. Single Medipix2 pixel Each 55µm Pixel has ~ 500 transistors using 0.25µm CMOS technology

  12. Readout Architecture 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 3328 bit Pixel Column 0 3328 bit Pixel Column 255 3328 bit Pixel Column 1 256 bit fast shift register 32 bit CMOS output LVDS out

  13. First test detector • Demountable detector • Simple lab vacuum, no photocathode • UV sensitive

  14. Initial Results It Works! Lower gain, higher rear field First light!

  15. Spatial Resolution Group 3-2 visible 9 lp/mm = 55µm (Nyquist limit) 100 µs 1 s

  16. Flat Field MCP deadspots Hexagonal multifiber boundaries 1200 cts/bin - 500Mcps

  17. Flat Field (cont) Histogram of Ratio consistent with counting statistics (2% rms) Ratio Flat1/Flat2

  18. 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

  19. 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 Acknowledgements This work was funded by an AODP grant managed by NOAO and funded by NSF Thanks to the Medipix Collaboration:

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