Transcript Noiseless, high frame rate (> kHz), photon counting arrays for use in the optical to extreme UV John Vallerga, Jason McPhate, Anton Tremsin and.

Noiseless, high frame rate (> kHz), photon
counting arrays for use in the optical to
extreme UV
John Vallerga, Jason McPhate, Anton Tremsin
and Oswald Siegmund
Space Sciences Laboratory, University of California, Berkeley
Bettina Mikulec and Allan Clark
University of Geneva
AMOS 2005 - Maui - J. Vallerga - [email protected]
Future WFS detector requirements
• High optical QE for fainter guide stars
• Lots of pixels - eventually 512 x 512
– More accuators
– More complex LGS images (parallax, gated, etc)
– Off null / open loop operation
• Very low (or zero!) readout noise
• kHz frame rates
AMOS 2005 - Maui - J. Vallerga - [email protected]
Photon Counting
Count
(x,y,t)
Events
Threshold
Charge integrating
Q
V  sv
AMOS 2005 - Maui - J. Vallerga - [email protected]
ADC
Events
 sEvents
Centroid in presence of noise:
1000 photons
100 photons
10 photons
8x8
Noiseless
35% QE
8x8
2.5 e- rms
90% QE
-
AMOS 2005 - Maui - J. Vallerga - [email protected]
-
6x6
2.5 e- rms
90% QE
-
4x4
2.5 e- rms
90% QE
Centroid error vs. input fluence
Centroid estimator error vs. technique
Centroid Error (rms, radians)
100.000
CCD Quad cell
CCD 8x8 weighted
CCD 6x6 weighted
Medipix 8x8 weighted
10.000
1.000
0.100
1
10
100
Input number of photons
AMOS 2005 - Maui - J. Vallerga - [email protected]
1000
Imaging, Photon Counting Detectors
Photocathode converts photon to electron
MCP(s) amplify electron by 104 to 108
Rear field accelerates electrons to anode
Patterned anode measures charge centroid
AMOS 2005 - Maui - J. Vallerga - [email protected]
Bandpass by photocathode selection
Quantum Efficiency
0.8
CsI
GaN
Bialkalai
GaAsP
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
200
400
600
Wavelength (nm)
AMOS 2005 - Maui - J. Vallerga - [email protected]
800
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)
AMOS 2005 - Maui - J. Vallerga - [email protected]
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
AMOS 2005 - Maui - J. Vallerga - [email protected]
Our AO detector concept
An optical imaging tube
using:
• GaAs photocathode
• MCPs to amplify to ~104
Photocathode
Photon
e-
Q = 104e-
Pij = Pij + 1
• Medipix2 ASIC readout
Window
AMOS 2005 - Maui - J. Vallerga - [email protected]
MCP
Medip ix2
Medipix2 ASIC Readout
 Each pixel has amp, discriminator, gate & counter.
 256 x 256 with 55 µm pixels (buttable to 512 x 512).
 Counts integrated at pixel. No charge transfer!
 Developed at CERN for Medipix collaboration (xray)
Previous Pixel
Shut ter
Mask bit
Lower Thresh.
Polarity
Mux.
Clock out
Disc.
Disc.
logic
Input
Preamp
Disc.
Mux.
13 bit
counter –
Shift
Register
Upper Thresh.
Mask bit
Next Pixel
Analog
Digital
AMOS 2005 - Maui - J. Vallerga - [email protected]
~ 500 transistors/pixel
First test detector
• Demountable detector
• Simple lab vacuum, no photocathode
• Windowless – UV sensitive
AMOS 2005 - Maui - J. Vallerga - [email protected]
UV photon counting movie
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
AMOS 2005 - Maui - J. Vallerga - [email protected]
Sub-pixel spatial linearity
Lamp
Pinhole
Detector
AMOS 2005 - Maui - J. Vallerga - [email protected]
Imaged pinhole array
Pinhole grid mask
(0.5 x 0.5 mm)
Gain: 20,000
Rear Field: 1600V
Threshold: 3 keGap: 500µm
AMOS 2005 - Maui - J. Vallerga - [email protected]
Avg. movement of 700 spots
0
Delta X
Centroid Position (µm)
-10
Delta Y
-20
-30
1 pixel
-40
-50
-60
-70
-80
-90
-100
0
5
10
15
Lamp Position (mm)
AMOS 2005 - Maui - J. Vallerga - [email protected]
20
25
Position error (550 events/spot)
50
Number of centroids
45
40
35
30
rms = 2.0 µm
25
20
15
10
5
0
-20
-15
-10
-5
0
5
10
Centroid difference (microns)
AMOS 2005 - Maui - J. Vallerga - [email protected]
15
20
Vacuum Tube Design
AMOS 2005 - Maui - J. Vallerga - [email protected]
Vacuum Tube Design
AMOS 2005 - Maui - J. Vallerga - [email protected]
Vacuum Tube Design
AMOS 2005 - Maui - J. Vallerga - [email protected]
Vacuum Tube Design
AMOS 2005 - Maui - J. Vallerga - [email protected]
Medipix on a Header
AMOS 2005 - Maui - J. Vallerga - [email protected]
Summary
• Noiseless detectors outperform CCDs
at low fluence per frame
• Photocathode choice to fit application
• Medipix ASIC readout allows for a huge
dynamic range, fast frame rate.
MCP/Medipix Status
• First tube in Fall 2005
• GaAs tube in 1st half of 2006
AMOS 2005 - Maui - J. Vallerga - [email protected]
Future Possibilities
• Medipix 3 now being discussed
–
–
–
–
130 nm CMOS technology
Faster front end for less deadtime per pixel
Faster readout rate (10 kHz frame rate)
Radiation hard
• Si APDs rather than MCPs as photon
converter/amplifier
– Higher optical QE
– Near IR response
– Cooling will be required to reduce dark count rate
AMOS 2005 - Maui - J. Vallerga - [email protected]
Acknowledgements
This work was funded by an AODP grant managed by
NOAO and funded by NSF
Thanks to the Medipix Collaboration:
•
Univ. of Barcelona
•
University of Napoli
•
University of Cagliari
•
NIKHEF
•
CEA
•
University of Pisa
•
CERN
•
University of Auvergne
•
University of Freiburg
•
Medical Research Council
•
University of Glasgow
•
Czech Technical University
•
Czech Academy of Sciences
•
ESRF
•
Mid-Sweden University
•
University of Erlangen-Nurnberg
AMOS 2005 - Maui - J. Vallerga - [email protected]
Flat Field
MCP deadspots
Hexagonal multifiber
boundaries
1200 cts/bin - 500Mcps
AMOS 2005 - Maui - J. Vallerga - [email protected]
Flat Field (cont)
Ratio Flat1/Flat2
AMOS 2005 - Maui - J. Vallerga - [email protected]
Histogram of Ratio
consistent with counting
statistics (2% rms)
Readout Architecture
• Pixel values are digital (13 bit)
3328 bit Pixel Column 255
3328 bit Pixel Column 1
3328 bit Pixel Column 0
• 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
256 bit fast shift register
32 bit CMOS output
LVDS out
AMOS 2005 - Maui - J. Vallerga - [email protected]
3328 bit Pixel Column 255
3328 bit Pixel Column 1
3328 bit Pixel Column 0
256 bit fast shift register
32 bit CMOS output
AMOS 2005 - Maui - J. Vallerga - [email protected]
LVDS out
“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
AMOS 2005 - Maui - J. Vallerga - [email protected]
EUV and FUV (50 - 200 nm)
CsI 1985 vs 1999
0.7
CsI 1985 30°
CsI 1985 20°
CsI #3 2/99 20°
CsI #3 2/99 30°
CsI #2 1/99 20°
CsI #2 1/99 30°
0.6
0.5
QDE
0.4
0.3
0.2
0.1
0
0
500
1000
Wavelength (Å)
AMOS 2005 - Maui - J. Vallerga - [email protected]
1500
2000
GaN UV Photocathodes, 100- 400 nm
AMOS 2005 - Maui - J. Vallerga - [email protected]
GaAsP Photocathodes
Hayashida et al. Beaune 2005 NIM
AMOS 2005 - Maui - J. Vallerga - [email protected]
Avalanche Photodiodes (APDs, Geiger mode)
•Single photon causes
breakdown in over-voltaged
diode
•QE potential of silicon
•Arrays in CMOS becoming
available
But
•Appreciable deadtime
•Low filling factor
•High dark counts, crosstalk
and afterpulsing
AMOS 2005 - Maui - J. Vallerga - [email protected]
APD arrays
32 x 32
Edoardo Charbon
Ecole Polytechnique Federale de Lausanne
AMOS 2005 - Maui - J. Vallerga - [email protected]
L3CCD (e2V Technologies)
•Integrates charge
•Multiplies charge in special
readout register
•Adjust gain such that se < 1e-
But
•Multiplication noise doubles
photon noise variance
•Single readout limiting frame
rate
AMOS 2005 - Maui - J. Vallerga - [email protected]
Assumed performance parameters
MedipixMCP
CCD
Binning
2x2
6x6
8x8
8x8
QE (%)
90
90
90
35
Readout
noise
2.5 e-
2.5 e-
2.5 e-
0
Seeing width
(pxls FWHM)
0.75
2.25
3
3
Diffract. width
(pxls FWHM)
0.5
1.5
2
2
AMOS 2005 - Maui - J. Vallerga - [email protected]
Gaussian weighted center of gravity
algorithm:
 N T   N  N 
(s )ph 
    

2ln(2)( N ph )  N D  2N  N 
2

(s )det
2


2
2
2
T
2
T
2
W
2
W
2
2
2


N T  N W 

s det

 
  

2
32(ln(2)) ( N ph )   N D 
2
3
(s 2 )tot  (s 2 )det  (s 2 )ph
From Fusco et al SPIE 5490. 1155, 2004
AMOS 2005 - Maui - J. Vallerga - [email protected]
2
Advantages of multi-pixel sampling of
Shack-Hartmann spots
Quad cell (2x2) algorithm for Gaussian input
Calculated position
1
Sigma
Sigma
Sigma
Sigma
Sigma
= 0.2
= 0.4
= 0.6
= 0.8
= 1.0
0
-1
-1
0
Centroid true position
1
Non-linearity of 2 x 2 binning
AMOS 2005 - Maui - J. Vallerga - [email protected]
Advantages of multi-pixel sampling of
Shack-Hartmann spots
4x4
6x6
4x4 COG non-linearity for Gaussian input
6x6 COG non-linearity for Gaussian input
1
Sigma = 0.4
Sigma = 0.8
Sigma = 1.2
0.5
Calculated position
(center of gravity)
Calculated position
(center of gravity )
1
0
-0.5
Sigma = 0.4
Sigma = 0.8
Sigma = 1.2
0.5
0
-0.5
-1
-1
-1
-0.5
0
0.5
1
Centroid true position
-1
-0.5
0
Centroid true position
Linear response off-null
Insensitive to input width
More sensitive to readout noise
AMOS 2005 - Maui - J. Vallerga - [email protected]
0.5
1
Technology advantage
High QE
CCDs
Number of pixels
CCDs, Medipix
Readout noise
APD, Medipix, L3CCD
Frame rate
Medipix, CCD
Gating
Medipix
AMOS 2005 - Maui - J. Vallerga - [email protected]
Quantum Detection Efficiency (%)
Soft X-Ray Photocathodes
100
CsBr
KI
80
60
40
20
0
0.1
AMOS 2005 - Maui - J. Vallerga - [email protected]
Energy (keV)
1