It's not just biological samples that the multi-photon microscopy platform of the Optics and Biosciences Laboratory* (LOB) is studying. Gaël Latour, a teacher-researcher at the University of Paris-Saclay, who carries out his research at the LOB at the École Polytechnique, applies this analysis technique to ancient objects, in particular parchments, as he presented at the IP Paris science day dedicated to light in September 2024. The aim is to provide detailed, objective information on their state of preservation, without altering them.