Pupil densification of obstructed monolithic apertures for high-contrast coronagraphy

UMR 6525 Astrophysique, University of Nice Sophia-Antipolis, 06108 Nice Cedex 2, France

Abstract

We give in this short communication the principle of the densification of a large classical on-axis aperture, with aperture central obscuration and spider arms into a full circular unobstructed aperture, for application to high-contrast coronagraphy. An example is shown using a VLT like aperture. In space, such a technique would allow to produce a perfect null of the star image using coronagraphic techniques such as the 4QC or the PKC, at the expense of a small reduction of the transmitted light. The drawback of the technique is that a surprisingly very small ZOF is obtained, if the telescope full resolution is considered. However, if a loss of resolution of a factor 2 is accepted, then the system might behave as a perfect imaging system. The technique is found useless for ground based observations with the Strehl ratios reached at the present time.