Abstract: Method and apparatus to ensure tuning without mode hopping of the resonator frequency and tuning of the Q-value of an optical resonator of the type comprising a partially reflecting resonator mirror (2) and a movable reflecting optical grating, with grooves (GR) parallel to the resonator mirror, intended to function as a wavelength selective reflector and which may comprise optical elements between the mirror and the grating, said optical elements being intended for collimation, amplification (4) and filtering of the radiation in the resonator, so that when changing the resonance wavelength (.lambda.) of the resonator or its Q-value, the grating is moved in such a way that a line (C) on the grating which is defined at a tuned initial position of the resonator by the intersection of the plane of grating grooves (M) and the virtual mirror plane (5) of the resonator mirror, remains at a distance less than .lambda.