E n tra n c e. W a v e. -fro n t. W. Focal. Plane. Pupil. Plane. Pupil. Plane. T. T. Spatial. Filter. Phase-. Shifting. Device. MACH-ZEHNDER. INTERFEROMETER. 1 ...
François Hénault, Alexis Carlotti, Christophe Vérinaud Institut de Planétologie et d’Astrophysique de Grenoble Université Grenoble-Alpes Centre National de la Recherche Scientifique BP 53, 38041 Grenoble – France
Conf. 10400 – Techniques and Instrumentation for Detection of Exoplanets VIII
San Diego, 08-10-17
1
Phase-shifting coronagraph
Plan of presentation • • • •
Goal of the study Principle Optical design Numerical model – Simulation of measures intensities – Wavefront reconstruction procedure
• Numerical simulations – Three different phase-shifting schemes – Three types of phase mask coronagraphs – Two typical wavefront errors (to be measured)
• Interpretation of the results • Conclusion
Conf. 10400 – Techniques and Instrumentation for Detection of Exoplanets VIII
San Diego, 08-10-17
2
Phase-shifting coronagraph
Goal of the study • Evaluate the measurement accuracy of wavefront sensing phase-shifting methods from inside a coronagraph • Put the phase-shifting device as far as possible within the coronagraph to compensate for Non common path aberrations (NCPA) • Compare phase-shifting in the pupil plane with phaseshifting in the image plane • Evaluate validity range: – Limited to weak aberrations or only by 2π-ambiguity [-λ/2,+λ/2] ? – Real or low-order wavefront sensor ?
Conf. 10400 – Techniques and Instrumentation for Detection of Exoplanets VIII
San Diego, 08-10-17
3
Phase-shifting coronagraph
A brief history of phase-shifting telescopes Primary Mirror
Entrance Wave-front W
Focal Plane
Secondary Mirror
Spatial Filter T
Pupil Plane PhaseShifting Device
1
Entrance Wave-front W
Secondary Mirror
Auxiliary Optics
Primary Mirror
TELESCOPE Focal Plane
Cylinder PZT
F. Hénault, Optics Communications (2006)
Focal Plane
Secondary Mirror
α Auxiliary Optics
Single Mode Optical Fiber
F. Hénault, Applied Optics (2005)
Entrance Wave-front W
TELESCOPE
Primary Mirror
Pupil Plane
R. Angel, Nature (1994)
3
TELESCOPE
2
MACH-ZEHNDER INTERFEROMETER
T
Entrance Wave-front W
TELESCOPE
Primary Mirror
ZERNIKE WAVEFRONT SENSOR Focal Plane
Secondary Mirror
4
Relay Optics
PhaseShifting Device
Parabolic Mirror
Pupil Plane
J. K. Wallace et al, Proc. SPIE (2011)
Conf. 10400 – Techniques and Instrumentation for Detection of Exoplanets VIII
San Diego, 08-10-17
4
Phase-shifting coronagraph
Principle • Three different phase-shifting schemes: Image mask plane
Lyot stop plane
T
T
O
T
1
T2
T O
O”’
O”
O’
3 - In coronagraph image plane
O”’
LOWFS
2 - In Lyot stop plane
O”
O’
T
1
- In telescope pupil plane
Coronagraphic plane
T
Phase-shifting device
Pupil plane
3
T
T
L1
L2
Conf. 10400 – Techniques and Instrumentation for Detection of Exoplanets VIII
Pupil plane
T
L3 San Diego, 08-10-17
5
Phase-shifting coronagraph
Optical design Phase-shifting in Pupil/Lyot stop plane
Phase-shifting in coronagraph image plane
Sensing in image plane
Phaseshift φm
L1
Phase mask
L2
Beam splitter
Sensing in pupil plane
L’5
M’2
M’1
Phaseshift φm
L1
Pick-off mirror
Phase mask
L2
Beam splitter
L4
M1
M’1
Pick-off mirror
M’2
M1
M2
T
Lyot stop
T
T
Combining mirror M3
T
L5 Lyot stop
M2
L3
Detectors in pupil plane
L6 Coronagraph image plane
BS2
L3
Detector in image plane
Conf. 10400 – Techniques and Instrumentation for Detection of Exoplanets VIII
Coronagraph image plane
San Diego, 08-10-17
6
Phase-shifting coronagraph
Numerical model • Module 1: Complex amplitude propagation from plane to plane via Fourier transforms (see next slides) • Module 2: Simplified WFE reconstruction procedure using two Dirac “Delta” approximations D d
