Experimental demonstration of a crossed cubes nuller for coronagraphy and interferometry François Hénault, Brahim Arezki Institut de Planétologie et d’Astrophysique de Grenoble, Université Grenoble-Alpes, CNRS, B.P. 53, 38041 Grenoble – France Alain Spang Laboratoire Lagrange, Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Parc Valrose, Bât. H. FIZEAU, 06108 Nice – France Y
eiπ/2
AT AT
eiπ/2
eiπ/2
eiπ/2 AR AT
eiπ/2
1
eiπ/2 AR AR
AR
X-polarized
AR AT
eiπ/2
π/2
π
-π/2
π
π
-π/2
π
π/2
eiπ/2 eiπ/2 Y
Y-polarized
AT AT
eiπ/2
AR AR
AT AR
X
Cubes polarization model
AT AR
Summary - Two “crossed” beamsplitter cubes have their semi-reflective layers perpendicular one to the other - The input beam propagates parallel to both cubes layers. It is spitted into four parallel beams, being recombined axially - Only two of those beams are used to generate a “null” at the focal plane centre - It is independent of wavelength and polarization orientation → This is actually an Achromatic phase shifter
Two beams (ATAT–ARAR)
Four beams
Interference fringes
eiπ
Z
AT
Two beams (ATAR–ARAT)
eiπ
Cube 2
Cube 1
256 pixels of 5.2 µm
Spectral power density
X
N ≈ 1.8 10-3 N ≈ 2.210-3 First fringes
Image plane Focusing optics Cube 1
Cube 2
Secondary Mirror
Advantages Monolithic telescope
(P)
Converging optics Diverging optics Fold mirror Beamsplitter or dichroïcs
Primary Mirror
Relay optics
Wavefront sensor
Crossedcubes nuller
Multi-axial combiner (exit pupil plane)
P’1
O’
(P’) P’2 F’
B’ Focal plane
O” Z
X”
Simple, compact, low mass and volume Reasonable manufacturing tolerances Potentially not expensive Not sensitive to chromatic flux mismatch Can be implemented into a nulling coronagraph telescope or a sparseaperture nulling interferometer • Very small Inner working angle (IWA) when used as a coronagraph • Capacity for fringes rotation and baseline modulation • Good candidate for future space missions characterizing extra-solar planets atmospheres • • • • •
B
P1
O
P2 (P)
Telescope 1
Telescope 2
Relay optics 1
Crossedcubes nuller
Relay optics 2
Fringe tracker 1-4 Tip-tilt sensors
Fringe tracker 2-3 Tip-tilt sensors
Fringe tracker 14-23
(P’) O’ F’
O”
Focal plane Z
Contacts
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