Johann Kolb, Norbert Hubin

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Detectors for LGS WF sensing on the E-ELT

• AO needs for detectors
• Derived specifications
• Solutions

• Johann Kolb, Norbert Hubin
• Mark Downing, Olaf Iwert, Dietrich Baade
• Simulation results
• Richard Clare

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AO Detectors needs on the E-ELT
Low order AO
IR Low order WFS
SH quad -cell
IR TT sensors
AO Detectors needs
PYR
Other WFS
on the E-ELT
NGS GLAO
LGS GLAO
NGS SCAO
Vis TT sensors
Guiding
LGS MCAO
MOAO
LTAO
XAO
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Adaptive Optics WFS detectors
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Specifications / Spatial resolution I
Large visible fast low-noise detector for
Shack-Hartmann based AO WFS
Specifications

• Spatial resolution
• Temporal resolution
• Image quality

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Specifications / Spatial resolution II

• Pixel size 24 µm ? Detector size 40x40 mm
• Compromise between reasonable detector size (for
  yield) and easiness of alignment with small pixels

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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

• 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

• 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

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Specifications / Temporal resolution II

• Image lag charges left behind lt 2 per
  pixel at the next frame.
• Is an issue for some technologies
• Is equivalent to reduction of AO bandwidth

• Full-well capacity gt 4000 electrons

• Linearity lt 5 peak-to-peak

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Specifications / Image quality I

• Average Read-Out Noise lt 3 e- rms/pixel/frame
  (goal lt1e-)
• Simulations ? in this range, required laser
  power increases linearly with RON

• Average Dark current lt 0.5 e-/pixel/frame
• Important at low frame rates

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Specifications / Image quality II

• Read-Out Noise and dark current variation
  95ile lt twice the average value
• Important in some technologies (CMOS) where all
  pixels dont have the same RON and dark current

• Simulations ? decreases performance with CoG,
  not much with Matched Filter

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Specifications / Image quality III

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

• Quantum Efficiency
• LGS mode gt 85 at 589 nm
• NGS mode

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Specifications / Image quality IV

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

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

• Example

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Other specifications

• Packaging

• Incidence angle

• Interfaces

• Pixel Response Non Uniformity

• Cosmetics

• Stability w/ temperature and time

• Lifetime

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Large visible fast low-noise detector for
Shack-Hartmann based AO WFS
Solutions that meet the specifications
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E-ELT AO WFS Detector Development Plan
Design Study
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CCD-based vs. CMOS-based concepts
Outside chip
On chip
Pixels

• Pre-amp.

• Charges creation

• Read-out (output register)

CCD Charge Coupled Device

• Controller, incl. digitization (ADCs)

• Charges transfer

• To the RTC

• Charges creation

• Pre-amp.

• Read-out (output register)

• Voltages transfer

CMOS Complimentary Metal Oxide Semiconductor

• Controller, incl. digitization (ADCs)

• Charges transfer

• Digitization (ADCs)

• To the RTC

• Read-out (pixels transistors)

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E-ELT AO WFS Detector design
Example frame transfer CCD CCD220
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Development status

• 3 Technology Demonstrator contracts awarded in
  2008
• 2 in manufacturing, results end of the year
• 1 completed
• frame rate of 1 kHz
• RON lt 2 electrons
• Image lag
• Pixel Response Non Uniformity
• Linearity
• Problems understood
• Forward path proposed

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

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The Universe
How to motivate detectors suppliers?
Entity
Provider
Role
Contain objects to observe
?
Atmosphere
Blur images
?
Telescope
Deliver the best possible image quality, with the
maximum throughput
EELT
WFS in adaptor or instrument
Provide pixels as representative as possible of
the image high spatial and temporal resolution,
high QE
WFS detector
YOU
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AO Detectors needs on the E-ELT
AO Detectors needs
on the E-ELT
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Large visible fast low-noise detector for
Shack-Hartmann based AO WFS
Specifications

• Spatial resolution
• Temporal resolution
• Image quality

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Specifications / Spatial resolution I

• Number of pixels 84x84 sub-apertures of 20x20
  pixels 1680 x 1680 pixels

To cover spot elongation in the most demanding AO
systems
Sodium layer
LLT
Pupil plane
Side launch
Detector plane
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Specifications / Spatial resolution III

• Angle of incidence the detector should accept
• F/10 to F/20
• Variable angle of incidence within a
  sub-aperture
• Maximum angle of incidence of 6.5º

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Wavefront sensors on the E-ELT

• 42 meters aperture
• NGS (broad wavelength range) or LGS (spot
  elongation)
• Schack-Hartmann (requires many pixels) or other
• Telescope or post-focal AO from 40 to 126
  sub-apertures
• 100 700 Hz (EPICS 3 kHz)
• Excellent image quality

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Example telescope GLAO

• Pre-focal station, PRELIMINARY design

• LGS WFS arms

• NGS WFS arms

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CCD vs. CMOS
Charges
Digital data
Voltages

• Pixels
• Transfer
• Read-out (output register)

• Pre-amplification
• Controller

• To the RTC

CCD Charge Coupled Device
CMOS Complimentary Metal Oxide Semiconductor

• Pixels
• Read-out (pixels transistors)

• Transfer
• Digitization (in ADCs)

• Controller
• To the RTC