Characterisation of the waveplate associated to layers in interferential mirrors Jonathan Agil, Bruno Letourneur, Sylvie George, Rémy Battesti and Carlo Rizzo Eur. Phys. J. Appl. Phys., 98 (2023) 61 Published online: 07 November 2023 DOI: 10.1051/epjap/2023230134