Johann Kolb, Norbert Hubin Mark Downing, Olaf Iwert, Dietrich Baade Simulation results: Richard...

Johann Kolb, Norbert Hubin Mark Downing, Olaf Iwert, Dietrich BaadeSimulation results: Richard Clare

Detectors for LGS WF sensing on the E-ELT

1AO for ELTs, Paris, 22-26 June 2009

AO needs for detectors Derived specifications Solutions

IR detectors development

Large visible fast low-noise detector for Shack-Hartmann based AO WFS

Existing visible high performance detector (i.e. CCD220)

3kHz low-noise detector

AO Detectors needs on the E-ELT

AO for ELTs, Paris, 22-26 June 2009

LGS GLAO

NGS GLAO NGS

SCAO

LGS MCAO LTAO MOAO

XAO

IR Low

order WFS

Low order AO

SH quad -cell

PYR Other WFS…

Vis TT sensors

IR TT sensors

2

Guiding

AO Detectors needs

on the E-ELT

Adaptive Optics WFS detectors


Existing system (MAD):8x8 sub-apertures on an e2v CCD39

In development (VLT AO Facility):40x40 sub-apertures on an e2v CCD220

Future (all EELT AO

modules):84x84 sub-

apertures

Specifications / Spatial resolution I


¤ Number of pixels: 84x84 sub-apertures of 20x20 pixels = 1680 x 1680 pixels

LLT

Sodium layer

Detector plane

Pupil plane

Side launch

flux

Need 14-20 pixels per sub-aperture

To cover spot elongation in the most demanding AO systems

Specifications


¤ Spatial resolution¤ Temporal resolution¤ Image quality

Specifications / Spatial resolution II


¤ Pixel size: 24 µm Detector size ~ 40x40 mmCompromise between reasonable detector size (for yield) and easiness of alignment with small pixels

¤ PSF = charge diffusion = optical cross-talk: 0.8 pixels “Blurs” the image Simulations PSF should be kept small

Specifications / Temporal resolution I


¤ Exposure time: variable between 1.4 and 5 / 10 (LGS / NGS) ms.

Corresponds to frame rates from 100 / 200 (NGS / LGS) to 700 Hz All specifications should be met at any value in this range

¤ Latency 1: synchronicity within a sub-aperture All pixels from a same sub-aperture should be exposed within 20 µs

¤ Latency 2: prompt and continuous transfer of pixel data to the detector output pins

¤ Read-out scheme : Either snapshot (frame-transfer CCD) or rolling-line (CMOS, NAOS IR sensor).

Rolling-line read-out = lines of pixels or of sub-apertures are read-out while the rest of the detector is integrating

Specifications / Temporal resolution II


¤ Image lag = “charges left behind”: < 2% per pixel at the next frame.

Is an issue for some technologies Is equivalent to reduction of AO bandwidth

¤ Full-well capacity: > 4000 electrons

¤ Linearity: < 5% peak-to-peak

Specifications / Image quality I


¤ Average Read-Out Noise: < 3 e- rms/pixel/frame (goal <1e-) Simulations in this range, required laser power increases linearly with RON

¤ Average Dark current: < 0.5 e-/pixel/frame Important at low frame rates

Specifications / Image quality II


¤ Read-Out Noise and dark current variation: 95%ile < twice the average value

Important in some technologies (CMOS) where all pixels don’t have the same RON and dark current

¤ Simulations decreases performance with CoG, not much with Matched Filter

Specifications / Image quality III


¤ Quantum Efficiency: LGS mode: > 85% at 589 nm NGS mode:

¤ The same detector shall be used either for LGS or NGS WF sensing

Specifications / Image quality IV


¤ One cannot always have large full-well capacity and very-low read-out noise CMOS allows regions of programmable gain.

lowest RON, small full-well (worst elongation)

low RON, average full-well

high RON (but still small w.r.t. photon noise), large full-well

System gain

(e-/ADU)

Full-well(e-)

Noise target

(e-)0.2 204 2.010.5 512 2.061 1024 2.242 2048 2.834 4096 4.278 8192 8.25

16 16384 16.12

¤ Example:

¤ Simulations (R. Clare) same performance as very low RON + large full-well, with Matched filter (degradation with CoG)

Other specifications


¤ Packaging

¤ Incidence angle

¤ Interfaces

¤ Cosmetics

¤ Pixel Response Non Uniformity

¤ Lifetime

¤ Stability w/ temperature and time



Solutions that meet the specifications

E-ELT AO WFS DetectorDevelopment Plan


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

1 (2?) contract – 1xFP7, (1xother?) 24 months Highly likely CMOS and down-select of TDs Retire architectural risks by fab. ~ ¼ imager

3 contracts – 2xFP6 ELT-DS, 1xEELT Phase B: 11 months All CMOS Imagers - most likely to succeed retire pixel risk by demonstration noise x speed with good imaging capability

4 contracts - 2xFP6 ELT-DS, 2xEELT Phase A: 6 months Investigated many different technologies Most promising – CMOS Image, APD array and orthogonal EMCCD

CCD-based vs. CMOS-based concepts


CCD:Charge Coupled Device

Outside chipOn chipPixels

Charges transfer

Read-out (output register)

Controller, incl. digitization (ADCs)

CMOS: Complimentary Metal Oxide Semiconductor

Charges creation

Pre-amp.

To the RTC

Charges transfer

Read-out (output register)

Controller, incl. digitization (ADCs)

Charges creation

Pre-amp.

To the RTC Read-out (pixels transistors)

Voltages transfer

Digitization (ADCs)

84x84 Sub-apertures

Analog processing

100s ADCs

Multiplexer/serializerY-a

dd

ressin

g

ControlLogic

Y-a

dd

ressin

g

ControlLogic

Analog processing

100s ADCs

Multiplexer/serializer

ControlLogic

ControlLogic

each 20x20 pixels

Vision of Full Size Device

E-ELT AO WFS Detector design


Example: frame transfer CCD: CCD220

Technology Demonstrator

Scaled Down Demonstrator

Development status


¤ 3 Technology Demonstrator contracts awarded in 2008 2 in manufacturing, results end of the year 1 completed:

frame rate of 1 kHzRON < 2 electronsImage lagPixel Response Non UniformityLinearity

Problems understood Forward path proposed

¤ 1 Scaled Down Demonstrator contract Call for Tender out this summer Contract start beginning 2010 Funded by EC

How to motivate detectors suppliers?


The Universe

Atmosphere

Telescope

WFS in adaptor or instrument

WFS detector

Entity Provider Role

Contain objects to observe

Blur images

Deliver the best possible image quality, with the maximum throughput

?

?

EELT

Provide pixels as representative as possible of the image: high spatial and temporal resolution,

high QE

Make the best use of received pixels to compute

turbulence correction

Wave Front reconstruction / Command to the Deformable Mirror

EELT

Johann Kolb, Norbert Hubin Mark Downing, Olaf Iwert, Dietrich Baade Simulation results: Richard...

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