Assessment of damage ranges by measurements of the refractive index in ion implanted LiNbO₃ and LiTaO₃

Ion implantation in LiNbO3 and LiTaO3 produces radiation damage by nuclear collisions. The amorphisation of the lattice reduces the refractive index of the material. In the case of fast ion bombardment with helium this damage layer is buried below the surface. The refractive index profile which then exists is suitable for an optical waveguide on the surface which supports several modes. Analysis of the refractive index profile yields the damage distribution in the crystal and this in turn can be compared with theoretical estimates of the damage production and ion ranges. Our analyses show that in the high energy range from 0.5 to 2.0 MeV the depth of the damage is predominantly controlled by the electronic stopping.