SPIE IR and Photoelect. Imagers and Detector Devices J. McPhate Jason McPhate, John Vallerga, Anton Tremsin and Oswald Siegmund Space Sciences Laboratory, University of California, Berkeley Bettina Mikulec and Allan Clark University of Geneva A noiseless, kHz frame rate, imaging detector base on MCPs readout with a Medipix2

SPIE IR and Photoelect. Imagers and Detector Devices J. McPhate WFS detector for future AO systems * kHz frame rates – Match atmospheric timescales Many pixels - eventually 512 x 512 –More subapertures and more pixels per subaperture Very low readout noise (< 3 e - ) –Lower penalty for more pixels per subaperture High (~80%) optical QE –Use dimmer guide stars or higher frame rates *Angel et al., “A Road Map for the Development of Astronomical AO”

SPIE IR and Photoelect. Imagers and Detector Devices J. McPhate 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, Count stored in digital histogram

SPIE IR and Photoelect. Imagers and Detector Devices J. McPhate 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 )

SPIE IR and Photoelect. Imagers and Detector Devices J. McPhate What’s the Catch? Global Counting Rates –1000 Shack-Hartmann spots per WFS –Kilohertz feedback rates –1000 counts per spot for sub-pixel centroids  1 Gigahertz counting rate! Quantum Efficiency –Historically Optical Photocathodes < ~15% –Silicon devices (CCDs) can get ~90% –Noiseless helps, but not that much  Requires integrating detector  Requires GaAs Photocathode

SPIE IR and Photoelect. Imagers and Detector Devices J. McPhate Our AO detector concept An optical imaging tube using: GaAs photocathode MCPs to amplify to ~10 4 Medipix2 ASIC readout

SPIE IR and Photoelect. Imagers and Detector Devices J. McPhate Medipix2 ASIC Readout  Pixelated readout for x and gamma ray semiconductor sensors (Si, GaAs, CdTe etc)  Developed at CERN for Medipix collaboration  55 µm 256 x 256 (abutable to 512 x [n x 256]).  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, x-ray diffraction, dynamic defectoscopy, etc.

SPIE IR and Photoelect. Imagers and Detector Devices J. McPhate Readout Architecture 3584 bit Pixel Column bit Pixel Column bit Pixel Column bit fast shift register 32 bit CMOS outputLVDS out Pixel values are digital (14 bit) Bits are shifted into fast shift register Choice of serial or 32 bit parallel output Maximum designed bandwidth is 100MHz Corresponds to 286µs frame readout in parallel

SPIE IR and Photoelect. Imagers and Detector Devices J. McPhate First test detector Demountable detector Simple lab vacuum (~10 -7 Torr) UV sensitive, no photocathode

SPIE IR and Photoelect. Imagers and Detector Devices J. McPhate Lab Detector Lessons Medipix ASIC works well as MCP readout Sub-pixel centroiding of Shack-Hartmann like spots was achieved Optimized parameters for use in optical tube –Chevron stack of 10 µm pore MCPs (protect cathode from ion feedback) –MCP gain of about 10 4 (longer tube life and higher counting rates) –MCP to Medipix gap of 300 to 500 µm (Medipix wirebond clearance) –Approximately 1600 V rear field (minimize MCP charge cloud spread)

SPIE IR and Photoelect. Imagers and Detector Devices J. McPhate Vacuum Tube Design No GaAs capability at UCB So GaAs photocathode by industrial vendor: Means using “standard” size tube Only marginally larger than the Medipix2 device

SPIE IR and Photoelect. Imagers and Detector Devices J. McPhate Thick Film Ceramic Header Internal mounting/GND surface for Medipix Route ~60 Medipix signals out of vacuum Multi-layered to better match Medipix pitch Maintain hermetic seal of tube to ≤10 -9 Torr Provide land pads for external I/F connectors

SPIE IR and Photoelect. Imagers and Detector Devices J. McPhate Vacuum Tube Design

SPIE IR and Photoelect. Imagers and Detector Devices J. McPhate Vacuum Tube Design

SPIE IR and Photoelect. Imagers and Detector Devices J. McPhate Vacuum Tube Design

SPIE IR and Photoelect. Imagers and Detector Devices J. McPhate Medipix on a Header

SPIE IR and Photoelect. Imagers and Detector Devices J. McPhate MCP/Medipix Serial I/F Board

SPIE IR and Photoelect. Imagers and Detector Devices J. McPhate Vacuum Tube Design

SPIE IR and Photoelect. Imagers and Detector Devices J. McPhate Vacuum Tube Design

SPIE IR and Photoelect. Imagers and Detector Devices J. McPhate Vacuum Tube Design

SPIE IR and Photoelect. Imagers and Detector Devices J. McPhate Vacuum Tube Design

SPIE IR and Photoelect. Imagers and Detector Devices J. McPhate Vacuum Tube Design

SPIE IR and Photoelect. Imagers and Detector Devices J. McPhate Parallel Readout Design Development by ESRF 1 to 5 Medipix2 chips FIFO for each chip Flat field, deadtime corrections Optional centroid calculation High speed serial out

SPIE IR and Photoelect. Imagers and Detector Devices J. McPhate Future Work (3 yr. NOAO grant) Seal a MCP/Medipix tube with a GaAs photocathode Perhaps a multi-alkali photocathode tube Finalize and build parallel readout Test at AO laboratory at CFAO, U.C. Santa Cruz Test at telescope

SPIE IR and Photoelect. Imagers and Detector Devices J. McPhate 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