Binary-star Wave Front Control Based on a Common-path Visible Nulling Coronagraph

Abstract

Exoplanets around multiple-star systems are interesting targets for direct detection. However, it is difficult to suppress unwanted light from all stars in a system. For direct detection of the exoplanets around multiple-star systems, we propose using common-path visible nulling coronagraphs (CP-VNCs). CP-VNCs can suppress diffracted light from stars located on a central null fringe. In addition, a wave front control system is installed to generate a dark hole by rejecting residual stellar speckles of CP-VNCs. For this purpose, spatial light modulators (SLMs) have the ability to generate a dark hole over a wide field on the order of hundreds of λ/D (where λ is the wavelength of light and D is the telescope diameter), owing to their large number of pixels. We perform a laboratory demonstration of high-contrast observation around a binary-star system model using a CP-VNC combined with an SLM. First, we simulate a high-contrast observation over a region close to one of two stars by generating a square dark hole with side lengths of 40 λ 0/D (where λ 0 is the central wavelength of the light sources). The center of the square region was located about 35 λ 0/D and 79 λ 0/D from each star. Measurements of this first scenario find a mean contrast over the dark hole of 3.5 × 10−8. Second, observation of a region with identical separation (100 λ 0/D) from both stars is also demonstrated. In this scenario, a mean contrast of 2.0 × 10−8 is achieved over a circular dark hole with a diameter of 40 λ 0/D.