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تسجيل مستخدم جديدImproved achromatization of phase mask coronagraphs using colored apodization
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For direct imaging of exoplanets, a stellar coronagraph helps to remove the image of an observed bright star by attenuating the diffraction effects caused by the telescope aperture of diameter D. The Dual Zone Phase Mask (DZPM) coronagraph constitutes a promising concept since it theoretically offers a small inner working angle (IWA sim lambda_0/D), good achromaticity and high starlight rejection, typically reaching a 1e6 contrast at 5 lambda_0/D from the star over a spectral bandwidth Deltalambda/lambda_0 of 25% (similar to H-band). This last value proves to be encouraging for broadband imaging of young and warm Jupiter-like planets. Contrast levels higher than 1e6 are however required for the observation of older and/or less massive companions over a finite spectral bandwidth. An achromatization improvement of the DZPM coronagraph is therefore mandatory to reach such performance. In its design, the DZPM coronagraph uses a grey (or achromatic) apodization. We propose to replace it by a colored apodization to increase the performance of this coronagraphic system over a large spectral range. This innovative concept, called Colored Apodizer Phase Mask (CAPM) coronagraph, is defined with some design parameters optimized to reach the best contrast in the exoplanet search area. Once this done, we study the performance of the CAPM coronagraph in the presence of different errors to evaluate the sensitivity of our concept. A 2.5 mag contrast gain is estimated from the performance provided by the CAPM coronagraph with respect to that of the DZPM coronagraph. A 2.2e-8 intensity level at 5 lambda_0/D separation is then theoretically achieved with the CAPM coronagraph in the presence of a clear circular aperture and a 25% bandwidth. In addition, our studies show that our concept is less sensitive to low than high-order aberrations for a given value of rms wavefront errors.
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In this paper is presented an analytical study of the azimuthal phase-mask coronagraph currently envisioned for detecting and characterizing extra-solar planets. Special emphasis is put on the physical and geometrical interpretation of the mathematic
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Phase apodization coronagraphs are implemented in a pupil plane to create a dark hole in the science camera focal plane. They are successfully created as Apodizing Phase Plates (APPs) using classical optical manufacturing, and as vector-APPs using li
quid-crystal patterning with essentially achromatic performance. This type of coronagraph currently delivers excellent broadband contrast ($sim$10$^{-5}$) at small angular separations (few $lambda/D$) at ground-based telescopes, owing to their insensitivity to tip/tilt errors.
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