Vector Apodizing Phase Plates for the ELT: From prototype to final optics for METIS and MICADO

Abstract

The first generation of instruments for the upcoming Extremely Large Telescope (ELT) will allow for the direct imaging of exoplanets that were previously below the sensitivity or resolution limits of existing facilities through various different High Contrast Imaging capabilities. Both METIS and MICADO will feature one or more Vector Apodizing Phase Plates (vAPP), a type of pupil-plane coronagraph based on liquid crystal technology that allows for broadband phase modification to create zones of high contrast around an observed point source. The METIS vAPPs will operate at L- and M-band wavelengths between 3.1 and 5.1 $μ$m, while the MICADO vAPP is optimized for shorter wavelengths in the J, H and Ks bands between 1.15 and 2.32 $μ$m. In this work, we will provide a brief introduction to this type of coronagraph, followed by a discussion of the commonalities and differences between the METIS and MICADO vAPP designs. In the last year, the final optics have been in production. During preparations for the manufacturing and also during the production phase,various challenges were encountered related to coating inclusions, uniformity of the optically active layers and adhesion between the substrates. Through simulations and empirical findings, we argue that the effects of these imperfections on the on the final optical performance are limited. We will present the expected contrast curves, discuss the current status and reflect on the implications for on-sky observations with METIS and MICADO.