Detectors for AO Wavefront Sensing

Detectors for AO Wavefront SensingMark Downing, G. Finger, D. Baade, N. Hubin, J. Kolb, O. Iwert

Instrumentation Division ESO

14/10/2009 1DfA 2009: AO WFS Detectors

Examine AO WFS Detector roadmap

Advanced Developments /

Tests at ESO

CCD220pnCCD

MPI/HLL

Future Developments

GMT, E-ELT, TMT

CCD39

CCD50

CCD60

CCID-26/128

CCID-35

MIT/LL

Past Detectors

http://www.dailygalaxy.com/photos/uncategorized/2007/09/03/giant_magellan_telescope_3_3.jpg

http://www.eso.org/projects/aot/mad/pictures/CCD39-01bi_large.jpg

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

2Control System computes

commands for the

deformable mirror(s)

3

Deformable mirror compensates the distorted

wavefront, achieving diffraction-limited resolution

4

OFF

ON


Challenge = Speed vs NoiseBiggest challenge for AO WFS detectors is the trade

between:

low noise (RON and dark current/count), and

fast frame rates

– becomes more difficult as format sizes increase

– and finally power dissipation limits feasibility

It is instructive to review how this trade has been achieved in the past.

14/10/2009 DfA 2009: AO WFS Detectors 3

Modelled Read Noise

0

2

4

6

8

10

12

14

16

1.E+04 1.E+05 1.E+06 1.E+07

Frequency (Hz)

NE

S e

lec

tro

ns

RM

S

CCD231 CCD230

e2v Technologies

Amplifier Pixel Rate pix/sec1 M 10 M100 k10 k

e2v

Read noise of output amplifier

Add more outputsAchieves lower read noise at fast frame rates by reading through multiple outputs.


More

amplifiers

Manufacturer Device Pixel size

Format (pixels)

Frame Rate

Outputs RON( rms)

QE

E2vCCD50 24μm 128x128 1000 fps 16 5e- ~ 90%

CCD39 24μm 80x80 1000 fps 4 10e- ~ 90%

MIT/LL CCID-26/64 21μm 64x64 600 fps 4 6-7e- ~ 90%

CCID-26/12 21μm 128x128 1000 fps 16 5e- ~ 90%

5-10e-5-10e-

Modelled Read Noise

0

2

4

6

8

10

12

14

16

1.E+04 1.E+05 1.E+06 1.E+07

Frequency (Hz)

NE

S e

lec

tro

ns

RM

S

CCD231 CCD230

e2v Technologies

Amplifier Pixel Rate pix/sec1 M 10 M100 k10 k

RON

e2v

Improve the amplifier design


MIT/LL

Achieves lower read noise by designing better amplifiers.

Improve

amplifier

• 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.

Electron

Multiplication

Register

E2v L3Vision:

<< 1 e- RON at output amplifier speeds of 16 Mpix/sec

• CCD60 128x128 24 µm pixel. 1,000 fps with 1 output.

• CCD220 240x240 24 µm pixel. 1,200 fps with 8 outputs.

Customize the architecture

Polar Co-ordinate CCD - talk about later

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.


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


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


Detectors in Advanced Development/

Test at ESO

MPI/HLLpnCCD

E2v CCD220

FUNDING: OPTICON FP6-WFSFUNDING: OPTICON FP6-WFS

SH 40 x 40 sub-ap.SH 40 x 40 sub-ap.

6x6 pixels/sub-ap.6x6 pixels/sub-ap.

240x240 pixels240x240 pixels

VLT Instruments SPHERE, VLT Instruments SPHERE,

AOF – MUSE and HAWK-IAOF – MUSE and HAWK-I

Past Detectors

Future Developments

GMT, E-ELT, TMT


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


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)

• Max Planck Institut /Halbleiterlabor

• pnCCD 256x256 pixels 51um pitch

• 450um thick fully depleted

excellent red response & no fringing

300V backside bias for good PSF

• Target: RON < 3e- at 1000 fps

• Split frame transfer

• Fast readout → Column Parallel CCD

one output amplifier per column

• Total of 528 amplifiers but

CAMEX (mux 132 to 1) for easy I/F

Only 8 analog output nodes


MPI/HLL

CAMEX 1 CAMEX 2

CAMEX 3 CAMEX 4

http://www.mpg.de/index.html

pnCCD: Testing at ESO funded by OPTICON FP6→ Excellent QE, PSF, and low read noise


QE: Excellent QE into the “Red” → good for Natural Guide Star applications. 450 µm thick silicon is able to collect the deep penetrating red photons.

PSF: Measured < 0.45 pixel over 400-900nm (exceeds specs of < 0.8 pixel). Pixels could be halved in size and still meet requirements.

RON: < 2.5 e-rms.

FP6FP6

51µm Pixel

Spot scanning used to measure PSF

Development to add APD output → AApnCCD (Avalanche Amplified pnCCD)

Part Funded by ESO and OPTICON FP6

14/10/2009 14DfA 2009: AO WFS DetectorsMPI/HLL

FP6

Add avalanche stage before output amplifier

Paper Lothar Strüder MPE/HLLPaper Lothar Strüder MPE/HLL

““Single Photon Counting in the OpticalSingle Photon Counting in the Optical””

Detectors for AO wavefront sensingMark Downing, G. Finger, D. Baade, N. Hubin, J. Kolb, O. Iwert

ODT / Instrumentation Division ESO


AO WFS roadmap

Future Developments

GMT, E-ELT, TMT Detector in Advanced

Development/

Test at ESO

Past Detectors

• Detectors required?

• Top Level Requirements

• Possible technologies

http://www.dailygalaxy.com/photos/uncategorized/2007/09/03/giant_magellan_telescope_3_3.jpg

AO Detector needs for ELTs


Large visible fast low-noise detector for

Shack-Hartmann based AO WFS

LGS Ground Layer

AO

NGS Groun

d Layer

AO

NGS Single

Conjugate AO

LGS Multi-

Conjugate AO

Laser Tomograph

y AO

Multi- Object

AO

3kHz ultra low-noise detector

Extreme AO

IR detectors development

IR WFS

IR TipTilt

sensors

Existing visible high performance detector

(i.e. CCD220)

Low Order

AO

Shack Hartmann

Quad -Cell

Pyramid Other

WFS…TipTilt Sensor

s Guiding

Large Visible AO WFS Detector needed Large Visible AO WFS Detector needed to sample the spot elongationto sample the spot elongation


Sodium Laser Guide Stars (589 nm)

• AO systems operate at ~1 kHz frame rate• Bright “guide stars” are required• Only 1% of the sky is accessible with natural

guide stars• Sodium layer at 80-90 km altitude can be

stimulated to produce artificial guide stars anywhere on the sky

• Pulsed laser can be used to range gate to limit laser spot elongation

LLT

Sodium layer

Detector plane

T ~ 10km

H ~ 80km

Distance from launch site

Pupil plane

Predicted spot elongation pattern

Large Visible AO WFS Detector Large Visible AO WFS Detector

Top Level RequirementsTop Level Requirements(developed from very detailed simulations)(developed from very detailed simulations)

• Ease of use/compact size:

integral Peltier

digital I/F preferred


Parameter Specification Comment

Array Format 1680x1680 pixels 84 x 84 sub-apert. each with 20x20 pixels to sample the spot elongation

Pixel Size 24-50 µm Large

Wavelength460-950nm (NGS)

589nm (LGS)Frame Rate 700 fps Fast

RON < 3 e- rms Low noise

QE > 80 % High

Dark Current < 0.5 e-/s/pixel Low

Storage Capacity < 4000e-/pixel Expect few photons

Cosmetics < 1.5% . Good; very few bad sub-apertures

Large Visible AO WFS Detector Large Visible AO WFS Detector Detector PlanDetector Plan

(Multi-Phase Development)(Multi-Phase Development)

19DfA 2009: AO WFS Detectors

Design Study

Design Study

Technology Validation

Development

Testing/ Acceptance

Production Phase

Technology Demonstrator

Scaled-down Demonstrator

2007

2008

2009

2010

2011

2012

2013

2014

2015

Authorize Production

Testing

30 Science Devices

Production

Full size device meeting all

specs.

Engineering exercise

Full Scale Demonstrator

Retire Architecture/ Process Risks

SDD

Retire Pixel Risks

TD

14/10/2009

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


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


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


ParameterSpecification

Minimum Goal

Array 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.


Several developments: see session on APDs on Thursday afternoonSeveral developments: see session on APDs on Thursday afternoon

Ian 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”

Teledyne SpeedsterTeledyne Speedster• Speedster128 (designed 2005)

• 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”


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.


THANK YOU


Documents

Detectors for AO Wavefront Sensing