Abstract: The invention disclosed herein relates to fibre lasers with intra-cavity frequency doubling. In one embodiment, the invention is directed to a fibre laser with intra-cavity frequency doubling characterized in that a non-linear crystal of type II phase matching is used to thereby enable operation of the fibre laser without selection of polarisation of the generated fundamental radiation. The non-linear crystal is oriented so as to minimise the walk-off angle of the second harmonic radiation, and a second dichroic mirror together with one of a plurality of focusing elements forms a telescopic reflector that provides for focusing and compensation of the spatial walk-off effect of the non-linear crystal.

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.