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 typical distance : few 10s mas
Context : Exoplanets Exoplanet detection is simple Potter et al., 2002, ApJ HD d=17.9 pcs 300 Myrs < 75 & 65 MJ@ 50 AU typical distance : few 10s mas There See faint objects (M 30) Need for High Contrast Imaging
For Disks : Disk morphology: warp, spirals, offsets, brightness assymetry, clumps Removing SED ambiguities For Planets : Spectral characterization Temporal variability (atmosphere) Orbital parameters 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: => residual speckles from static aberrations => 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 Self-Coherent Camera Instrument Self-Coherent Camera (SCC)
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 Simple set-up : SCC + Four Quadrant Phase Mask coronagraph (FQPM)
= Intensity in focal plane
The SCC in 3 Planes coronagraphic pupil reference pupil D DR a Pupil plane Optical propagation + Intensity in focal plane FFT Pupil correlation Plane a The SCC image processing
I- = TF-1[P ** PR ] FFT-1 Ic = I + IR + Iplanet FFT-1 I+ = TF-1[ P * PR* ] FFT-1 Use I+ to mesure phase (hidden in P ) (I+ is almost a linear function of for small phase) Focal plane wavefront sensor(Galicher et al. 2008) Use I+ and Ic to detect Iplanet (Ic codes I and IR but not Iplanet) Planet detection instrument (not described here) (Baudoz et al. 2006, Galicher & Baudoz 2007) Where is the phase in SCC image ?
For coronagraphic image : P = ei - with pupil function and ~1 The phase is almost a linear function of the imaginary parts With small phase defects : P = i linear function of P imaginary part real part Simulation: FQPM +SCC + phase only 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. E-ELT (infinite exposure time)
SCC + E-ELT (infinite exposure time) ELT 42m DSP (20 cm pitch - 64nm residual) 10 nm static defects Infinite exposure time + perfect coronagraph SCC Phase versus time 10 ms 100 ms 1 s 10 s Static phase
ELT 42m +perfect coronagraph DSP (20 cm pitch - 64nm residual) 10 nm static defects coherent time = 10 ms in H SCC Phase versus time 10 ms 100 ms 1 s 10 s Static phase 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 Time evolution 2 layers, only temporal error = 1ms
Fixed aberrations =5 nm 2 layers, only temporal error = 1ms 40x40 actuators, m, L0=20m, V0=10m/s About 35 nm on pupil 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 Limitations 1: Chromatism
1% 2% 5% bandwidth=15% Solution 1: Wynne corrector bandwidth=15% same +Wynne corrector effective bandwidth =0.75% Solution 2 : Chromaticity of residual speckles requires spectral resolution SCC coupled with IFS Limitations 2: Reference Zeroeffect Limitations 3: Coronagraph effects
FQPM+SCC Matrix Zernikes Zernikes Phase measurement with a Prototype
FQPM SCC detector Pupil plane Lyot plane Defocus of the source to test the SCC with a theoretical amplitude of 1.8 nm Phase difference image for 1.8 nm Test Bench Development
Integration started in May 09 See Marion Mas (poster yesterday !!!) 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