1 September 2017 Development status and performance of the evanescent wave coronagraph testbed
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Abstract
The Evanescent Wave Coronagraph (EvWaCo) is a new kind of “band-limited coronagraph” that involves the tunneling effect to suppress the starlight, thus producing the coronagraphic effect. The first advantage is that this mask adapts itself to the wavelength due to the evanescent wave properties, yielding nearly an achromatization of the star extinction. The second advantage is that the starlight can be collected for astrometry and/or wavefront analysis and correction. NARIT has developed a specific optical setup operating over the spectral band [780 nm, 880nm] to demonstrate highlevel contrasts and inner working angles in line with the requirements for exoplanet detection. Our aims are: to test and characterize the EvWaCo performance in diffraction-limited regime, to install a simulator of turbulence and an adaptive optics setup to simulate ground-based observations, and to define the best scheme for the wavefront correction. The preliminary results obtained in diffraction-limited regime demonstrated contrasts equal to a few 10-6 at a distance between 10 and 20 λ/D from the Point Spread Function (PSF) center with an unpolarized source emitting at λ1 = 880 nm with a relative spectral bandwidth Δλ/λ1 ≈ 6%. In this paper, we first describe the upgraded setup and present the results of the performance characterization that investigates the variation of the contrast with the wavelength and with the polarization. Then, we show the results obtained on the star channel and demonstrate the capability to measure in real time the star PSF profile and position. Finally, we discuss the future improvements to optimize the performance.
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Mary Angelie Alagao, Christophe Buisset, Yves Rabbia, Thierry Lepine, Saran Poshyachinda, Boonrucksar Soonthornthum, "Development status and performance of the evanescent wave coronagraph testbed", Proc. SPIE 10400, Techniques and Instrumentation for Detection of Exoplanets VIII, 104001Q (1 September 2017); doi: 10.1117/12.2272901; https://doi.org/10.1117/12.2272901
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