Development of the Savart-plate lateral-shearing interferometric nuller for exoplanet (SPLINE)

Abstract

The Savart-Plate Lateral-shearing Interferometric Nuller for Exoplanet (SPLINE) is a stable and fully achromatic nulling interferometer proposed for direct detection of extrasolar planets with segmented-mirror telescopes like the Thirty Meter Telescope (TMT). The SPLINE uses a Savart plate, a kind of polarizing beam splitter, to split a light beam into two orthogonally polarized ones with a lateral shift. The Savart plate placed between crossed polarizers causes fully achromatic destructive interference for an on-axis star light. On the other hand, planetary light from an off-axis direction does not destructively interfere due to the lateral shift. The SPLINE provides a stable interferometric output because of its simple common-path optical design without an optical-path difference control system. We carried out laboratory demonstrations of the SPLINE to evaluate its stability, achromaticity, and achievable contrast. As a result, a high contrast of >10⁴ (peak-to-peak contrast) is achieved using a broadband light source as a star model. In addition, we also propose to apply a differential imaging technique to the SPLINE for improving achievable contrast. We report our recent activities and show the results of the laboratory demonstrations.