a noiseless 512 x 512 detector for ao with khz frame rates
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
SPIE Instrumentation for Astronomy AO - June22, 2004
John Vallerga, Jason McPhate, Anton Tremsin and Oswald Siegmund
Space Sciences Laboratory, University of California, Berkeley
Bettina Mikulec and Allan ClarkUniversity of Geneva
A noiseless 512 x 512 detector for AO with kHz
frame rates
SPIE Instrumentation for Astronomy AO - June22, 2004
Future WFS Requirements*
• High (~80%) optical QE• Lots of pixels - eventually 512x512• Very low readout noise (< 3 e-)• kHz frame ratesThe last three are not simultaneously
achievable with the current generation of CCDs
*Angel et al “A Road Map for the Development of Astronomical AO”
SPIE Instrumentation for Astronomy AO - June22, 2004
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
Charge distribution on stripsCharge CloudMCP stackTube Window withphotocathodeγ
SPIE Instrumentation for Astronomy AO - June22, 2004
Microchannel Plates
2 µm pores on 3 µm centers (Burle Industries)
SPIE Instrumentation for Astronomy AO - June22, 2004
MCP Detectors at Berkeley
85 mm
10 mm
400 pxl
14000 pxl
COS FUV for Hubble (2004,2005,???)
25 mm Optical Tube
68 mm
GALEX NUV Tube (in orbit)
SPIE Instrumentation for Astronomy AO - June22, 2004
GaAs Photocathodes (GenIII)
• Developed for night vision tubes
• Slight cooling required (104 cps at room temp)
• Only fabricated in USA and Japan
SPIE Instrumentation for Astronomy AO - June22, 2004
Advantages of multi-pixel sampling of Shack Hartman spots
Linear response off-nullInsensitive to input widthMore sensitive to readout noise
2 x 2 5 x 5
SPIE Instrumentation for Astronomy AO - June22, 2004
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
SPIE Instrumentation for Astronomy AO - June22, 2004
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
SPIE Instrumentation for Astronomy AO - June22, 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.
SPIE Instrumentation for Astronomy AO - June22, 2004
Single Medipix2 pixel
Input
Preamp
Disc.
Disc. logic Mux. 13 bit
counter –ShiftRegister
Clock out
Shutter
Lower Thresh.
Disc.
Mux.
Previous Pixel
Mask bit
Analog Digital
Upper Thresh.
Next Pixel
Mask bit
Polarity
Each 55µm Pixel has ~ 500 transistors using 0.25µm CMOS technology
SPIE Instrumentation for Astronomy AO - June22, 2004
Readout Architecture33
28 b
it P
ixel
Col
umn
0
3328
bit
Pix
el C
olum
n 25
5
3328
bit
Pix
el C
olum
n 1
256 bit fast shift register
32 bit CMOS output LVDS 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
SPIE Instrumentation for Astronomy AO - June22, 2004
First test detector
• Demountable detector• Simple lab vacuum, no photocathode• UV sensitive
SPIE Instrumentation for Astronomy AO - June22, 2004
Initial Results
It Works!
First light! Lower gain, higher rear field
SPIE Instrumentation for Astronomy AO - June22, 2004
Spatial Resolution
100 µs 1 s Group 3-2 visible 9 lp/mm = 55µm
(Nyquist limit)
SPIE Instrumentation for Astronomy AO - June22, 2004
Flat Field
1200 cts/bin - 500Mcps
MCP deadspots
Hexagonal multifiber boundaries
SPIE Instrumentation for Astronomy AO - June22, 2004
Flat Field (cont)
Histogram of Ratio consistent with counting
statistics (2% rms)Ratio Flat1/Flat2
SPIE Instrumentation for Astronomy AO - June22, 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
SPIE Instrumentation for Astronomy AO - June22, 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