Design, analysis, and testing of a microdot apodizer for the apodized pupil Lyot coronagraph (Research note). III. Application to extremely large telescopes

TL;DR

This paper presents the design, testing, and validation of a microdot apodizer for the apodized pupil Lyot coronagraph, demonstrating its suitability for extremely large telescopes like the European-ELT with high contrast performance.

Contribution

The study introduces a new microdot apodizer specifically designed for ELT-sized telescopes, showing improved manufacturing accuracy and confirming the APLC's effectiveness for high-contrast imaging.

Findings

Peak attenuation of 295 achieved.

Contrast levels of 10^-5 at 7 λ/D and 10^-6 at 12 λ/D.

Performance maintained across a 24% wavelength band.

Abstract

The apodized-pupil Lyot coronagraph is one of the most advanced starlight cancellation concepts studied intensively in the past few years. Extreme adaptive optics instruments built for present-day 8m class telescopes will operate with such coronagraph for imagery and spectroscopy of faint stellar companions. Following the development of an early demonstrator in the context of the VLT-SPHERE project (~2012), we manufactured and tested a second APLC prototype in microdots designed for extremely large telescopes. This study has been conducted in the context of the EPICS instrument project for the European-ELT (~2018), where a proof of concept is required at this stage. Our prototype was specifically designed for the European-ELT pupil, taking its large central obscuration ratio (30%) into account. Near-IR laboratory results are compared with simulations. We demonstrate good agreement with theory. A peak attenuation of 295 was achieved, and contrasts of 10^-5 and 10^-6 were reached at 7 and 12 lambda/D, respectively. We show that the APLC is able to maintain these contrasts with a central obscuration ratio of the telescope in the range 15% to 30%, and we report that these performances can be achieved in a wide wavelength bandpass (BW = 24%). In addition, we report improvement to the accuracy of the control of the local transmission of the manufactured microdot apodizer to that of the previous prototype. The local profile error is found to be less than 2%. The maturity and reproducibility of the APLC made with microdots is demonstrated. The apodized pupil Lyot coronagraph is confirmed to be a pertinent candidate for high-contrast imaging with ELTs.