METHOD AND DEVICE FOR COUPLING OUT A PARTIAL BEAM HAVING A VERY SMALL BEAM PERCENTAGE FROM AN OPTICAL BEAM

The invention relates to a device comprising a beam splitter and a method of using the device. The device comprises a beam emitting unit and a downstream beam splitter, which is formed by two adjacent planar plates of different materials. For a specified wavelength range of an optical beam from which a partial beam is to be coupled out by reflection, the material of the first planar plate has a minimum refractive index which is greater by a refractive index interval than the maximum ref ractive index of the material of the second planar plate. From the optical beam, which, collimated and linearly polarized parallel to a plane of incidence, impinges on the beam splitter at a certain angle of incidence, the partial beam having only a small summary percentage of the optical beam and a small spectral fluctuation range is coupled out.