E2V Technologies L3 Detector Schematic

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E2V Technologies L3 Detector Schematic
Multiplication register
Store Area
Image Area
Avalanche multiplication takes place in
Multiplication Register, using an HV clock
(40-45Volts).
Normal Serial register
Multiplication register
1e- in
1000e- signal out
Multiplication register
Standard MOSFET amplifier
Devices used
CCD60 128 x 128
CCD87/97 512x512
CCD201 1K x 1K
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Appearance of L3 Bias Frame
Dominated by Clock Induced Charge (CIC)
Histogram of conventional CCD bias frame.
Vertical scale in electrons
Histogram of L3 CCD bias frame.
Cut along Image row
The L3 bias contains almost entirely single
electron events, however, a cut through the image
shows events with a wide range of heights. This
distribution has the effect of reducing the SNR
at higher illumination levels.
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Multiplication Noise
The statistics of the multiplication process give
a range of output signals in response to a single
electron input.

• Normal photon statistics
• do not apply, instead the
• RMS variation of the signal
• (2xmean signal).
• Equivalent to an effective
• halving of QE

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L3 SNR gains and losses
L3 wins due to zero read noise
L3 loses due to multiplication noise
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L3 Applications

• Low flux regimes normally limited by detector
  read noise
• Adaptive Optics Wave-front sensing.
• High time resolution imaging/spectroscopy.
• Lucky Astronomy

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GLAS
Ground-layer Laser Adaptive optics System
25W Rayleigh Laser beacon. Height defined by
hi-speed Pockels cell shutter. On-axis laser
guide star will give full sky coverage, however,
natural guide star still required for tip-tilt
correction.
beacon 20 km
turbulence laser
Comes into operation Autumn 2006
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Need for a Natural Guide Star
Laser beacons are insensitive to global
tip-tilt terms because of the double passage of
the laser through the turbulent layer.
A field star close to the science object must be
observed for tip-tilt correction. Note that
guide star availability limits sky coverage
now Insert diagram of sky coverage
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NAOMI/GLAS System Schematic
Wavefront Re-constructor
Corrected NIR science image
Primary
DM
Pockels cell
Shack-Hartmann WFS observing Laser Guide Star
(LGS). CCD39
FSM
Pulsed Rayleigh Laser
Tip-Tilt WFS observing Natural Guide Star
(NGS). L3 CCD60
Larger errors Off-loaded to TCS
Detail of Shack Hartmann Sensor
Conjugate planes
FSMfast steering mirror (tip tilt wave-front
error correction) DMdeformable mirror (to remove
higher order errors)
Image displacement on CCD proportional to average
wave-front gradient
Wave-front
CCD
Lenslet array conjugate with primary aperture
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INGs L3 Wavefront Sensor
Redundant slave controller replaced with CCD60 L3
WFS Head in May 2005. Initial tests as a Shack
Hartmann sensor, although will finally be used
for Natural Guide Star tip-tilt sensing.
NAOMI AO system WFS Heads
New L3 Head
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Expected GLAS performance

• FWHM using R17th mag tip-tilt star
• Not diffraction limited in visible wavelength
  range
• but seeing improvement tool

I Band image
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The CCD60 as a Shack Hartmann NGS Wavefront
Sensor prior to the commissioning of GLAS
Main focus of our work is to use the CCD60 as a
tip-tilt sensor for GLAS, in the meantime,
however, we hope to use it in SH mode to
overcome the current noise limitations of the
(non-laser) WFS.
Predicted gains from using L3 NGS sensor on
current NAOMI AO system
Sequence of L3 CCD60 images taken on William
Herschel Telescope NAOMI adaptive optics system
Data supplied by Richard Wilson, Univ. Durham
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SDSU Performance
All work done with SDSUII controller custom
built HV generator board insert picture of
board
Pixel read 1.2us Pixel skip 560ns Just fast
enough for our current applications!
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Hi Time Resolution Photometry
Example observation Crab Nebula Pulsar using L3
CCD60 on the WHT
CCD60 Test Camera
Sub-electron read noise at 180 frames per second
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Larger Format Detectors
512 and 1K square detectors incorporated into
cryogenic cameras
QUCAM1 CCD87 QUCAM2 CCD201
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Hi Time Resolution Spectroscopy
Example observation IP Pegasus, eclipsing
binary Using L3 CCD87 on the WHT
Ha
White dwarf with accretion disc in orbit
around larger primary star. Accretion disc
luminosity dominates and its light is highly
doppler shifted.
Sequence of raw spectra, taken using CCD87 L3
Camera
-500km/s
500km/s
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Lucky Astronomy
Hi frame rates are used to freeze atmospheric
motion. Frames corrupted by turbulence are then
discarded. Remaining frames shifted and added to
take out tip-tilt motions. Near diffraction
limited images result. awaiting input from
Craig Mackay
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Future possibilities Photon Counting

• There is no longer any loss of SNR due to
  multiplication noise.
• L3 CCD performance then approaches that of the
  ideal detector.
• Low CIC essential

Threshold
Cryogenic CCD87 imaging a faint pinhole
Raw input frames
Thresholded and accumulated
Particles? Waves?