SPIE IR and Photoelect. Imagers and Detector Devices - 2005 - 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
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SPIE IR and Photoelect. Imagers and Detector Devices - 2005 - J. McPhate Jason McPhate, John Vallerga, Anton Tremsin and Oswald Siegmund Space Sciences.
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SPIE IR and Photoelect. Imagers and Detector Devices - 2005 - 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 - 2005 - 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 - 2005 - J. McPhate
Imaging, Photon Counting DetectorsCharge distribution on stripsCharge CloudMCP stackTube Window withphotocathodeγ
Photocathode converts photon to electron
MCP(s) amplify electron by 104 to 108
Rear field accelerates electrons to anode
Patterned anode measures charge centroid,Count stored in digital histogram
SPIE IR and Photoelect. Imagers and Detector Devices - 2005 - 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
– LN2 not required
– Low dark current (0.16 attoamps cm-2)
SPIE IR and Photoelect. Imagers and Detector Devices - 2005 - 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 - 2005 - J. McPhate
Our AO detector concept
An optical imaging tube using:
0
10
20
30
40
50
60
200 400 600 800 1000
Bialkali (Hamamatsu)
Extended S25 (Hamamatsu)
Extended S25 (Photonis)
GaAs (ITT)
Quantum Efficiency (%)
Wavelength (nm)
• GaAs photocathode
• MCPs to amplify to ~104
• Medipix2 ASIC readout
SPIE IR and Photoelect. Imagers and Detector Devices - 2005 - 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 pixel @ 256 x 256 (abutable to 512 x [n x 256]).