noiseless, high frame rate (> khz), photon counting arrays for use in the optical to extreme uv
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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AMOS 2005 - Maui - J. Vallerga - [email protected]
John Vallerga, Jason McPhate, Anton Tremsin and Oswald Siegmund
Space Sciences Laboratory, University of California, Berkeley
Bettina Mikulec and Allan Clark
University of Geneva
Noiseless, high frame rate (> kHz), photon counting arrays for use in the optical to
extreme UV
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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
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AMOS 2005 - Maui - J. Vallerga - [email protected]
Photon Counting
QADC
V v
EventsEvents
Charge integrating
Threshold
EventsCount(x,y,t)
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AMOS 2005 - Maui - J. Vallerga - [email protected]
Centroid in presence of noise:
8 x 8Noiseless35% QE
10 photons
- - -
100 photons
1000 photons
8 x 82.5 e- rms90% QE
6 x 62.5 e- rms90% QE
4 x 42.5 e- rms90% QE
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AMOS 2005 - Maui - J. Vallerga - [email protected]
Centroid error vs. input fluence
Centroid estimator error vs. technique
0.100
1.000
10.000
100.000
1 10 100 1000
Input number of photons
Centroid Error (rms, radians)
CCD Quad cellCCD 8x8 weightedCCD 6x6 weightedMedipix 8x8 weighted
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AMOS 2005 - Maui - J. Vallerga - [email protected]
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
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AMOS 2005 - Maui - J. Vallerga - [email protected]
Bandpass by photocathode selection
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 200 400 600 800
Wavelength (nm)
Quantum Efficiency
CsIGaNBialkalaiGaAsP
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AMOS 2005 - Maui - J. Vallerga - [email protected]
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)
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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
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AMOS 2005 - Maui - J. Vallerga - [email protected]
Our AO detector concept
An optical imaging tube using:
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10
20
30
40
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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
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AMOS 2005 - Maui - J. Vallerga - [email protected]
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)
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
~ 500 transistors/pixel
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AMOS 2005 - Maui - J. Vallerga - [email protected]
First test detector• Demountable detector
• Simple lab vacuum, no photocathode
• Windowless – UV sensitive
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AMOS 2005 - Maui - J. Vallerga - [email protected]
UV photon counting movie
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
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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 ke-
Gap: 500µm
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AMOS 2005 - Maui - J. Vallerga - [email protected]
Avg. movement of 700 spots
-100
-90
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-50
-40
-30
-20
-10
0
0 5 10 15 20 25
Lamp Position (mm)
Centroid Position (µm)
Delta X
Delta Y
1 pixel
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AMOS 2005 - Maui - J. Vallerga - [email protected]
Position error (550 events/spot)
0
5
10
15
20
25
30
35
40
45
50
-20 -15 -10 -5 0 5 10 15 20
Centroid difference (microns)
Number of centroids
rms = 2.0 µm
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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
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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
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AMOS 2005 - Maui - J. Vallerga - [email protected]
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
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AMOS 2005 - Maui - J. Vallerga - [email protected]
Flat Field
1200 cts/bin - 500Mcps
MCP deadspots
Hexagonal multifiber boundaries
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AMOS 2005 - Maui - J. Vallerga - [email protected]
Flat Field (cont)
Histogram of Ratio consistent with counting
statistics (2% rms)Ratio Flat1/Flat2
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AMOS 2005 - Maui - J. Vallerga - [email protected]
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
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AMOS 2005 - Maui - J. Vallerga - [email protected]
3328
bit
Pix
el C
olum
n 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
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AMOS 2005 - Maui - J. Vallerga - [email protected]
“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
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AMOS 2005 - Maui - J. Vallerga - [email protected]
0
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0 500 1000 1500 2000
CsI 1985 vs 1999
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°
Wavelength (Å)
EUV and FUV (50 - 200 nm)
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AMOS 2005 - Maui - J. Vallerga - [email protected]
GaN UV Photocathodes, 100- 400 nmGaN UV Photocathodes, 100- 400 nm
0.1
1
10
100
150 200 250 300 350 400
NW-BH071#3
NW-BH071#2
NW-JG238#3
NW-JG238#2
Quantum Efficiency (%)
Wavelength (nm)
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AMOS 2005 - Maui - J. Vallerga - [email protected]
GaAsP Photocathodes
Hayashida et al. Beaune 2005 NIM
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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
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AMOS 2005 - Maui - J. Vallerga - [email protected]
APD arrays
Edoardo CharbonEcole Polytechnique Federale de Lausanne
32 x 32
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AMOS 2005 - Maui - J. Vallerga - [email protected]
L3CCD (e2V Technologies)
•Integrates charge
•Multiplies charge in special readout register
•Adjust gain such that e < 1e-
But
•Multiplication noise doubles photon noise variance
•Single readout limiting frame rate
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AMOS 2005 - Maui - J. Vallerga - [email protected]
Assumed performance parameters
CCDMedipix-
MCP
Binning 2 x 2 6 x 6 8 x 8 8 x 8
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
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AMOS 2005 - Maui - J. Vallerga - [email protected]€
(σ Δφ2 )ph =
π 2
2ln(2)(Nph )•NTND
⎛
⎝ ⎜
⎞
⎠ ⎟
2
•NT
2 + NW2
2NT2 + NW
2
⎛
⎝ ⎜
⎞
⎠ ⎟
2
(σ Δφ2 )det =
π 3
32(ln(2))2•σ det
(Nph )
⎛
⎝ ⎜
⎞
⎠ ⎟
2
•NT
2 + NW2
ND
⎛
⎝ ⎜
⎞
⎠ ⎟
2
(σ Δφ2 )tot = (σ Δφ
2 )det +(σ Δφ2 )ph
Gaussian weighted center of gravity algorithm:
From Fusco et al SPIE 5490. 1155, 2004
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AMOS 2005 - Maui - J. Vallerga - [email protected]
Advantages of multi-pixel sampling of Shack-Hartmann spots
Non-linearity of 2 x 2 binning
Quad cell (2x2) algorithm for Gaussian input
-1
0
1
-1 0 1 Centroid true position
Calculated position
Sigma = 0.2
Sigma = 0.4
Sigma = 0.6
Sigma = 0.8
Sigma = 1.0
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AMOS 2005 - Maui - J. Vallerga - [email protected]
Advantages of multi-pixel sampling of Shack-Hartmann spots
Linear response off-nullInsensitive to input widthMore sensitive to readout noise
4 x 4 6 x 64x4 COG non-linearity for Gaussian input
-1
-0.5
0
0.5
1
-1 -0.5 0 0.5 1
Centroid true position
Calculated position(center of gravity )
Sigma = 0.4Sigma = 0.8Sigma = 1.2
6x6 COG non-linearity for Gaussian input
-1
-0.5
0
0.5
1
-1 -0.5 0 0.5 1
Centroid true position
Calculated position(center of gravity)
Sigma = 0.4Sigma = 0.8Sigma = 1.2
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AMOS 2005 - Maui - J. Vallerga - [email protected]
Technology advantage
High QE CCDs
Number of pixels CCDs, Medipix
Readout noise APD, Medipix, L3CCD
Frame rate Medipix, CCD
Gating Medipix
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AMOS 2005 - Maui - J. Vallerga - [email protected]
Soft X-Ray Photocathodes
0
20
40
60
80
100
0.1 1
CsBr
KI
Energy (keV)