Abstract: The invention relates to dispersion interferometers for measuring a dispersion portion of the refractive index of an investigated medium by an interferometric method and can be used in the optical industry and in the composition of diagnostic complexes of various plasma installations of the type of Tokamak, Stellarator, gas-discharge lasers. The dispersion interferometer comprising a radiation source, two nonlinear optical doublers of frequency at a distance ensuring a location of an object under examination therebetween, a light filter means and a recording device, all arranged along an optical axis. Additionally provided is a polarization beam splitter, and the two non-linear optical frequency doublers are so oriented that the directions of polarization of fast waves are orthogonal to each other and do not coincide with ones separated by the beam splitter and the radiation source.