Fabrication of optical waveguides in KGW by swift heavy ion beam irradiation

Irradiations with F, O at 25 MeV and C at 14 MeV energy have been performed in KGd(WO4)2 (KGW) in order to fabricate optical waveguides by a novel route based on ion irradiation instead of ion implantation. The method relies on selecting the energy high enough so as to place the maximum of the electronic stopping power a few microns inside the crystal. Then, buried isotropic layers (amorphous-like) are formed which have a low refractive index value of 1.87 (compared to the three crystalline values which are above 2.0). The refractive index profiles obtained are Gaussian-like with O ions and more step-like with the usage of C ions. Fairly low fluences in the range 1 x 1013-1 x 1014 have been successfully explored. The results have been compared to those recently obtained for LiNbO3 and have been analyzed with a theoretical model based on thermal spike concept