François Nez (DR CNRS, LKB Hydrogen Spectroscopy) performs ultra-high precision hydrogen spectroscopy and QED tests. Research: (1) 1S–3S hydrogen/deuterium spectroscopy — continuous-wave laser, optical frequency comb via REFIMEVE network, theory comparison at ppt level; (2) muonic hydrogen/atom spectroscopy — CREMA collaboration at PSI; determines proton charge radius with record precision; (3) GRASIAN — gravitational quantum states of hydrogen atoms and neutrons; probing short-range forces beyond Standard Model. Primarily fundamental physics rather than sensing applications, but uses precision optical metrology infrastructure.