Abstract: A method and device for reducing the thermal-mechanical motion of a defecting body is disclosed, in which the device includes a semiconductor injection laser used as both a light source and a dual-mirror optical cavity for precisely measuring the motion of the body. The thermally induced motion of the mechanical structure is quenched using a force-feedback technique, in which the information from the structural-motion detector is coupled to the forcing mechanism such that the motion of the deflecting structure is counteracted and thereby reduced.