A possible new experimental test of the wavelengthindependence of the velocity of light in vacuum

It is proposed that the velocity of light be compared at two frequencies using the radiation of a laser with a narrow spectrum and its harmonic. If the velocities of light at these frequencies are not equal, the corresponding wavelengths are not exact multiples. Therefore, a comparison of the wavelengths—which can be made using a Fabry–Perot interferometer—can give information on the relative difference between the velocities (Δc/c). The use of radiation with a spectral width of Δν/ν~10^–11 and of an interferometer with a 3-m base should make it possible to detect Δc/c=10^–11.