The SelfCoherent Camera: a focal plane wavefront sensor for EPICS

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The Self-Coherent Camera a focal plane wavefront
sensor for EPICS

• P. Baudoz

R. Galicher, M. Mas, J. Baudrand, G. Rousset, A.
Boccaletti, F. Assemat
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Context Exoplanets
Exoplanet detection is simple
See faint objects (M ?30)
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Need for High Contrast Imaging

• For Disks
• Disk morphology warp, spirals, offsets,
  brightness assymetry, clumps
• Removing SED ambiguities

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EPICS - Planet Finder of the E-ELT
Lessons learned from SPHERE and GPI studies
(still to be confirmed) If XAO is working as
expected (raw contrast 104 to 106) Need
calibration (102 to 103) but limitations gt
residual speckles from static aberrations gt
residual speckles are chromatic (2nd order if
careful optical design)
Need Phase measurement from final science focal
plane. Need Separate post-processing data
reduction for each spectral bandwidth
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Self-Coherent Camera Principle
Telescope
Slow Servo-loop (quasi-static aberrations)
XAO (DM)
Self-Coherent Camera (SCC)
Beam splitting
Spatial Filter
Coronagraph
Beam recombining (Fizeau Fringes)
Image Processing
Planet Detection
Image
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Simple set-up SCC Four Quadrant Phase Mask
coronagraph (FQPM)


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The SCC in 3 Planes
Pupil plane
Optical propagation
Intensity in focal plane

FFT
Pupil correlation Plane
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The SCC image processing
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Where is the phase in SCC image ?
For coronagraphic image
P ?eiF - ??????????????with ? pupil function
and ?1
linear function of P
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Is SCC a real wavefront sensor ?

• No it is much better than that
• It measures directly the complex amplitude of the
  field in the focal plane (including amplitude
  effects).
• BUT
• Phase estimation at high frequency rate (exposure
  time shorter than coherent time)
• Not competitive compared to other WFS
  (chromaticity)
• Long exposure time
• Blurring of fringes for the residual speckles
  after XAO
• Only static speckles are fringed.

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E-ELT (infinite exposure time)
SCC

• ELT 42m
• DSP (20 cm pitch - 64nm residual)
• 10 nm static defects
• Infinite exposure time perfect coronagraph

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• ELT 42m perfect coronagraph
• DSP (20 cm pitch - 64nm residual)
• 10 nm static defects
• coherent time 10 ms in H

SCC Phase versus time
100 ms
10 ms
10 s
1 s
Static phase
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Noise level in the corrected area

• E-ELT 42m perfect coronagraph
• DSP (20 cm pitch - 64nm residual)
• 10 nm static defects
• coherent time 10 ms in H
• 90 of the corrected area

0.1 nm level
These levels depends linearly on coherent time
(10 ms) and quadratically on residual turbulent
level (64 nm RMS)
1 nm level
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Time evolution
Fixed aberrations 5 nm
2 layers, only temporal error 1ms 40x40
actuators, r01m _at_1.6 ?m, L020m, V010m/s About
35 nm on pupil
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And if static are not static
Quasi-static aberrations fully decorrelated
after 20s
4.6 nm
Simulation XAO sampling 1ms Sampling of SCC 1s
0.45 nm
0.25 nm
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Limitations 1 Chromatism
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Limitations 2 Reference  Zero  effect
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Limitations 3 Coronagraph effects
FQPMSCC Matrix
Zernikes
Zernikes
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Phase measurement with a Prototype
SCC detector
Lyot plane
Pupil plane
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Test Bench Development
Integration started in May 09
See Marion Mas (poster yesterday !!!)
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Conclusion

• Phase estimation
• Optimized for long exposure time (10s seconds to
  mesure 1nm level- EPICS case)
• Simple set-up with Lyot and phase mask
  coronagraph
• To be coupled with IFS because of chromatism (or
  need more advanced estimator)
• Deeper study on-going (closed loop,
  chromatism,)
• Coupling with planet detection to be studied in
  more details (especially for the long exposure
  time case)
• Need more laboratory test