Construction of EXIST (Exoplanet Imaging System Testbed) toward future space coronagraphs

Abstract

Development of a high-contrast imaging system, especially toward direct detection of habitable Earth-like exoplanets, would be one of the most challenging themes in modern astronomy. For direct detection of exo-Earth, coronagraphic devices are required for suppressing bright diffracted light from a parent star. In addition, residual stellar speckles, caused by imperfection of optical components, have to be also rejected by wavefront control such as the speckle nulling technique. It is important to construct a dedicated testbed at which we can comprehensively develop the high-contrast imaging system for future era of space coronagraphs aimed at searching for exo-Earths. Recently, we have started construction of a new testbed in Japan which is called EXIST (Exoplanet Imaging System Testbed). The EXIST is planned to be compatible with various types of coronagraphs, such as phase-mask coronagraphs based on the photoniccrystal technology, common-path visible nulling coronagraph, and so on. In addition, optimally designed pupil apodizers will be installed into the testbed for maximizing the performance of the phase-mask coronagraphs with arbitrary aperture telescopes. We plan to utilize a spatial light modulator (SLM) for conducting the speckle nulling control. Thanks to a large pixel format of the SLM, we expect that a huge dark hole can be created against the residual speckles. Here, we report our recent progress on the construction of the new testbed and results of some preparatory experiments related to the coronagraphs and the speckle nulling control using the SLM.