Solar System planetology requires a wide use of observing spectroscopy for surface geology to atmosphere climatology. A high-contrast imaging is required to study and to characterize extra-solar planetary systems among other faint astronomical targets observed in the vicinity of bright objects. Two middle class space telescopes projects aimed to observe Solar system planets by a long term monitoring via spectroscopy and polarimetry. Extra solar planets (exoplanets) engineering and scientific explorations are included in science program.
Direct imaging of earth-like extrasolar planets in the habitable zone and the search for possible biological signatures are
among the key scientific objectives in the modern astronomy. Stellar coronagraph such as achromatic interfero
coronagraph (AIC) with a small inner working angle has limited possibilities to detect and characterize planets around
nearby stars due to the star leakage effect caused by incomplete suppression of the star of finite angular size. We report
on an improved instrument for direct imaging of exoplanets and the study of stellar environment – common-path
achromatic interfero-coronagraph with variable rotational shear (common-path achromatic rotation-shearing
coronagraph, CP-ARC) – a common path implementation of rotation shearing interferometer. We detail CP-ARC
approach and discuss its optical configuration, laboratory prototype and experimental results.
We propose to use an extremely unbalanced interferometer (EUI) as a wavefront correcting input to a stellar coronagraph
for direct exoplanet imaging. Since a cumulative wavefront error causes incomplete suppression of stellar light, an EUI
aims to correct precisely the wavefront incident to the coronagraph to a level better than λ/5000 in the visible wavelength
range. EUI does not use an extremely precise deformable mirror, it increases the accuracy of a wavefront control
effectively because of the coherent summation with an amplitude imbalance. It will enable obtaining the desirable 10-9
coronagraphic (raw) contrast for Earth-like exoplanet imaging.
We propose to use an extremely unbalanced interferometer (EUI) as a wavefront correcting input to a stellar coronagraph for direct exoplanet observation. Since wavefront error causes incomplete suppression of stellar light, an EUI aims to precisely correct the wavefront incident on the coronagraph to a level better than λ/5000 in the visible wavelength range. Compared to the previous unbalanced interferometer, which incorporated a nulling function, the proposed EUI does not introduce the nulling function. EUI does not use a precise deformable mirror. It increases the accuracy of a wavefront control effectively because of the coherent summation with an amplitude imbalance. It enables obtaining the desirable 10−9 coronagraphic contrast for Earth-like exoplanet imaging.
Stellar coronagraphs with a small inner working angle have limited possibilities to detect exoplanets due to the star leakage effect caused by incomplete suppression of the star of finite angular size. We consider an improved instrument for direct imaging of exoplanets: common-path achromatic interfero-coronagraph with variable rotational shear (CP-ARC). CP-ARC reduces the star leakage effect by several orders of magnitude (with small angles of rotational shear relative to a fixed angle of 180 deg) with telescope size more than 1 m. Operation capacity of CP-ARC was experimentally verified by laser light nulling and white light nulling with lab prototype treated.
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