Detectors for AO Wavefront Sensing Mark Downing, G. Finger, D. Baade, N. Hubin, J. Kolb, O. Iwert Instrumentation Division ESO 14/10/2009 1 DfA 2009: AO WFS Detectors Examine AO WFS Detector roadmap Advanced Development s / Tests at ESO CCD220 pnCCD MPI/HLL Future Developments GMT, E-ELT, TMT CCD39 CCD50 CCD60 CCID-26/128 CCID-35 MIT/ LL Past Detectors
Future Developments GMT, E-ELT, TMT . Advanced Developments / Tests at ESO. Past Detectors. CCID-35. CCID-26/128. CCD50. pnCCD. CCD220. CCD60. Examine AO WFS Detector roadmap. Detectors for AO Wavefront Sensing. CCD39. Mark Downing, G. Finger, D. Baade, N. Hubin, J. Kolb, O. Iwert - PowerPoint PPT Presentation
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Detectors for AO Wavefront SensingMark Downing, G. Finger, D. Baade, N. Hubin, J. Kolb, O. Iwert
Adaptive Optics (AO) - removing the twinkle of the stars
Wavefronts from astronomical objects are distorted by the Earth’s atmosphere, reducing the spatial resolution of large telescopes to that of a 10 cm telescope
1
Wavefront Sensor measures deviation of wavefront from a flat (undistorted) wave
Achieves lower read noise by designing better amplifiers.
Improveamplifier
• Type of amplifier (JFET or MOSFET, “p” or “n”).• Geometry (WxL) of amplifier.• Oxide thickness.• Reduce capacitances (floating diffusion and parasitic).
→ The higher the conversion gain the lower is the noise.
Refer back to talk by Vyshnavi Suntharalingam, Refer back to talk by Vyshnavi Suntharalingam, ““Advanced Imager Technology Development at MIT Lincoln LaboratoryAdvanced Imager Technology Development at MIT Lincoln Laboratory” ”
• Barry Burke (MIT/LL) CCID-56 160x160 21 µm pixel 20 outputs:– New pJFET amplifier design – Reporting ~ 2.5 e- at 1 Mpix/sec (800fps)
• 256x256 by 21 µm pixel, 32/64 outputs in development
614/10/2009
Add EMCCD gain in the serial register
Rf1 Rf2 Rf3
If1If2If3
Rf2HV
DfA 2009: AO WFS Detectors
Achieves lower read noise by adding electron multiplication register before the amplifier.
ElectronMultiplication
Register
E2v L3Vision: << 1 e- RON at output amplifier speeds of 16 Mpix/sec
Curvature CCD, CCID-35 – R. Dorn (ESO), J. Beletic, and B. Burke (MIT/LL).– 8x10 subapertues,– RON < 1.2e- at 4 kfps and QE > 80%,– Successfully used in upgrade to FlyEyes at CFHT.
14/10/2009 DfA 2009: AO WFS Detectors 7
Storage Area #1
Storage Area #2
Image Area – 20x20 18µm pixels
Buffer Serialregister
MIT/LL
Sub-aperture design Array design
Achieves lower read noise by minimizing the number of pixels read out by custom designing the architecture to the application.
See poster Kevin Ho, “See poster Kevin Ho, “Flyeyes: Upgrade of CFHT’s AO System Using an MIT-LL CCID 35 SensorFlyeyes: Upgrade of CFHT’s AO System Using an MIT-LL CCID 35 Sensor” ”
Add gain in the pixel => APD
• Build detector from array of single APDs or better an APD array.• Downside is silicon APDs have statistical variation of gain that results in an
excess noise factor of ~ 2-3• Overcome by operating the APD in high gain “Geiger” mode to discriminate and
count single photon events and thus essentially offer zero read noise.
e.g. PoliMI SPADA (Single Photon Avalanche Diode Arrays) 80 APDs QE ~ 40% dark count rates < 3000 counts/sec/pixel Photon counter → zero read noise at 20 kfps
14/10/2009 DfA 2009: AO WFS Detectors 8
p+ substrate
np
e h
SPADA
Achieves lower read noise by Electron Multiplication Gain in the pixel.
Detectors for AO wavefront sensingMark Downing, G. Finger, D. Baade, N. Hubin, J. Kolb, O. Iwert
ODT / Instrumentation Division ESO
14/10/2009 9DfA 2009: AO WFS Detectors
Detectors in Advanced Development/Test at ESO
MPI/HLLpnCCD
E2v CCD220
FUNDING: OPTICON FP6-WFSFUNDING: OPTICON FP6-WFSSH 40 x 40 sub-ap.SH 40 x 40 sub-ap.6x6 pixels/sub-ap.6x6 pixels/sub-ap.
240x240 pixels240x240 pixelsVLT Instruments SPHERE, VLT Instruments SPHERE, AOF – MUSE and HAWK-IAOF – MUSE and HAWK-I
Past Detectors
Future Developments GMT, E-ELT, TMT
14/10/2009 DfA 2009: AO WFS Detectors 10
StoreArea
Image Area
240x12024□µm
StoreArea
Image Area
240x12024□µm
OP 1
OP 2 GainRegisters
OP 3
OP 4 GainRegisters
OP 8GainRegisters
OP 7
OP 6GainRegisters
OP 5
e2v CCD220
e2v CCD220: Split frame transfer CCD 240x240 24 µm pixels 8 L3Vision EMCCD outputs << 1 e- RON at 1,200 fps
Metal Buttressed2Φ 10 Mhz Clocks
for fast image to store transfer rates. 8 L3Vision Gain
Registers/OutputsEach 15Mpix./s.
Next talk Philippe FeautrierNext talk Philippe Feautrier““OCam and CCD220 - World's Fastest and Most Sensitive Astronomical CameraOCam and CCD220 - World's Fastest and Most Sensitive Astronomical Camera ” ”
FP6
Several Test Cameras in operation → built by LAM, LAOG, OHP
CCD220 Status
14/10/2009 11DfA 2009: AO WFS Detectors
Devices in house that meet specs.
Technology
transfe
rred
ESO’s NGC WFS Camera Head is at advanced stage of prototype
Reported in Javier REYES posterReported in Javier REYES poster““ESO AO Wavefront Sensor Camera”ESO AO Wavefront Sensor Camera”
MPI/HLL pnCCD(Robert Hartmann, Sebastian Ihle, Heike Soltau, Lothar Strueder)
Scaled Down Demonstrator Retire architectural risks by fab. ~ ¼ imager Highly likely CMOS Usable device on Telescope
Several Technology Demonstrators All CMOS Imagers - most likely to succeed retire pixel risk by demonstration noise x speed with good imaging capability (no image lag)
Several Design Studies Investigated many different technologies Most promising – CMOS Imager, APD array and orthogonal EMCCD
20
transfergate
supplyvoltage
2
34
1
columnoutput
FDPPD
reset
Readtransfergate
supplyvoltage
2
34
1
columnoutput
FDPPD
reset
Read
With recent improvements CMOS now rival CCDsWith recent improvements CMOS now rival CCDs
1. Pinned Photo Diode → low dark current (10 pA/cm2) 0.5 e-/pix/frame with modest cooling (-10 DegC)
2. High conversion gains (200 µV/e-) → low RON of < 2e-
- by reducing sense node capacitance < 0.8 fF
3. Buried channel MOSFETs → reduces/eliminates RTS signal noise
4. Build from thicker high resistivity silicon and ‘substrate biasing’ low crosstalk and good red response
5. Multi-sample the pixel at different conversion gains (µV/e-) improves dynamic range and linearity
PLUS the long offered advantages of4. Fast frame rates → highly parallel readout: ultimate of amplifier per pixel.
5. Low power → µA instead of mA (CCD) transistor bias currents.
6. Monolithic integration of support circuitry; biases, sequencer, clocks, ADCs…
Offers a simple, easy-to-use digital interface.
14/10/2009 DfA 2009: AO WFS Detectors
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Polar Co-ordinate CCDPolar Co-ordinate CCD
Read out fewer pixels
Customizes CCD architecture to: minimize no. of pixels to be read out reduce image to store transfer time conceived by Jim Beletic, Sean Akins of KECK; Barry Burke (MIT/LL) being developed by Sean Akins, Brian Aull, Brad Felton (MIT/LL)
-
- and Robert Reich)
Serial Register
Imaging Area
Image Clocks
Storage Clocks
Storage Area
Typical subaperture
Clock annulus
Typical pixel array
Laser projectionpoint
14/10/2009 DfA 2009: AO WFS Detectors 22
Na LayerNa Layer
PulsedPulsedLaserLaser
Pulsed laser: track spot on CCD Pulsed laser: track spot on CCD
and move charge back and forth to collect photons from several pulses
before reading out.
Spot contained in much smaller number of
pixels and only these need to be read out
Clock CCD charge with
the spot
10 annuli clocked separately to optimally track spot
CCD needs to be customized:– for each new application, or
– application configured or restricted to use existing CCD; e.g. use center projected laser and < 60x60 sub-apertures.
Scalability:– May not be scalable to 120x120 sub-apertures
512 amplifiers could be challenging.
IR AO WFS Detectors RequirementsIR AO WFS Detectors Requirements
• RON has limited use to low order Tip/Tilt and “Truth” sensors
– Scientific detectors used: HAWAII-XRG (10e-) and the PICNIC (20e-)–
• For E-ELT much better detectors are needed:– e-APD– Teledyne Speedster
14/10/2009 DfA 2009: AO WFS Detectors 23
ParameterSpecification
Minimum GoalArray Format 256x256 pixels
Pixel Size 18-40 µm 40 µm
Wavelength 0.8-2.5 µm
Frame Rate 750 fps 1500 fps
RON < 5 e- rms 3 e- rms
QE > 70 % > 80 %
Dark Current < 3 e-/s/pixel < 1 e-/s/pixel
Storage Capacity (e-/pix) 10k 20k
Talk David Hale “Low-noise IR Wavefront Sensing with a Teledyne HxRG” Talk David Hale “Low-noise IR Wavefront Sensing with a Teledyne HxRG”
e-APDse-APDs• APDs in linear mode have excess noise factor, F > 1
– Typically 2-3 for silicon and 3-5 for III-V materials
• In HgCdTe: F ~ 1 in linear mode has been demonstrated– E.g. LETI: gain of 5300 and F ~ 1.05-1.3 at reverse bias of 12.5V.
– impact ionization occurs mostly by single carrier, electrons, rather than the larger, slower, and less deterministic holes.
• ESO has funded SELEX to develop a 24 µm 320x256 prototype detector:– λc = 2.5 µm– Prototype operational and initial results are encouraging.
14/10/2009 DfA 2009: AO WFS Detectors 24
Several developments: see session on APDs on Thursday afternoonSeveral developments: see session on APDs on Thursday afternoonIan Ian BAKER (SELEX)BAKER (SELEX), ,
““HgCdTe Avalanche Photodiode Arrays for Wavefront Sensing and Interferometry Applications”.HgCdTe Avalanche Photodiode Arrays for Wavefront Sensing and Interferometry Applications”.
Don Hall (IfA and Teledyne),Don Hall (IfA and Teledyne), ““Electron-Avalanche and Hole-Avalanche HgCdTe Photodiode Arrays for Astronomy”Electron-Avalanche and Hole-Avalanche HgCdTe Photodiode Arrays for Astronomy”
Johan Rothman (Johan Rothman (CEA Leti-MinatecCEA Leti-Minatec),), ““APD Development at CEA Leti-Minatec”APD Development at CEA Leti-Minatec”
• 128 x 128 pixels• 40 µm pixel pitch• Digital input – clocks and biases generated on-chip• Analog output • Two gain settings – high gain for lowest noise• Chip functionality and performance (in low gain) proven• High gain mode (which should be lowest noise) does not work as designed
• Speedster256-D (designed 2008)• fix of Speedster128 design• Improved CTIA pixel• 256 x 256 pixels• 12 bit analog-to-digital converters on-board• Up to 10 kHz frame rate
27/6/2008 Detectors for AO WFS 25
Refer back to Jim Beletic’s talk Refer back to Jim Beletic’s talk ““Teledyne Imaging Sensors - Producer of detectors with a dynamic range of 1 million....in several dimensions” Teledyne Imaging Sensors - Producer of detectors with a dynamic range of 1 million....in several dimensions”
14/10/2009 25DfA 2009: AO WFS Detectors
Conclusion• Current detector developments at ESO are on track to meet current
instrument needs.
• Innovative detector developments are required for the ELTs.
• ESO is actively involved with Detector Manufacturers to lay the foundations to meet these needs.