L- and M-band annular groove phase mask in lab performance assessment on the vortex optical demonstrator for coronagraphic applications

Coronagraphy is a high-contrast imaging technique that aims to reduce the blinding glare of a star to detect a potential companion in its close environment. Vortex phase mask coronagraphy is widely recognized as one of the most promising approaches. The vortex optical demonstrator for coronagraphic application (VODCA) is a test bench currently developed at the University of Liège. Its main goal is to optically characterize infrared phase masks, in particular vortex masks. We detail the layout and salient features of VODCA and present the performance of the latest L-band (3575 to 4125 nm) and M-band (4600 to 5000 nm) annular groove phase masks (AGPMs) manufactured by our team. We obtain the highest rejection ratio ever measured for an AGPM at L-band: 3.2 × 10³ in a narrowband filter (3425 to 3525 nm) and 2.4 × 10³ in a broad L-band filter. By providing measurements close to the intrinsic limit of science-grade AGPMs, VODCA proves to be a step forward in terms of the evaluation of vortex phase masks performance.