The system described permits the wavelength of a helium-neon laser to be controlled at any value within the available bandwidth. A second laser, used as a reference, has its wavelength controlled at a specific value, e.g. the peak of the intensity profile, and beats between the two radiations are used to generate a correcting signal for the first laser. The resulting wavelength-stabilized output is free of modulation and can be used for long distance interferometry.