Apodized Lyot Coronagraph for VLT-SPHERE: Laboratory tests and performances of a first prototype in the visible

TL;DR

This paper reports on laboratory tests of a prototype Apodized Lyot Coronagraph designed for the VLT-SPHERE instrument, demonstrating its manufacturing process, optical performance, and sensitivity to misalignments in the visible spectrum.

Contribution

It introduces a new apodizer prototype for the ALC, including its design, manufacturing process, and performance evaluation in laboratory conditions.

Findings

Successful fabrication of the apodizer with specified transmission profile

Achieved nulling performances close to theoretical expectations

Identified sensitivity of the ALC to component misalignments

Abstract

We present some of the High Dynamic Range Imaging activities developed around the coronagraphic test-bench of the Laboratoire A. H. Fizeau (Nice). They concern research and development of an Apodized Lyot Coronagraph (ALC) for the VLT-SPHERE instrument and experimental results from our testbed working in the visible domain. We determined by numerical simulations the specifications of the apodizing filter and searched the best technological process to manufacture it. We present the results of the experimental tests on the first apodizer prototype in the visible and the resulting ALC nulling performances. The tests concern particularly the apodizer characterization (average transmission radial profile, global reflectivity and transmittivity in the visible), ALC nulling performances compared with expectations, sensitivity of the ALC performances to misalignments of its components.