Influence of swift ions and proton implantation on the formation of optical waveguides in lithium niobate

Optically polished titanium doped congruent lithium niobate single crystals were implanted with protons of energy of $120keV$ (at fluences of $1×1015$⁠, $1×1016$⁠, and $1×1017ions∕cm2$⁠). Some loss of lithium from the surface upon ion implantation was recovered by irradiation with $50MeV$ lithium ions (at fluences varying from $1×1011to1×1013ions∕cm2$⁠). The near surface region defects created in the crystal were analyzed using high resolution x-ray diffraction technique, atomic force microscopy, fourier transform infrared, and optical transmittance (UV-visible) studies. The marked lattice strain induced by the energetic ions was characterized by high resolution x-ray diffraction measurements. Three-dimensional defect clusters were observed from atomic force microscopy with nanoscale resolution. Variations of O–H bond stretching vibrations as a function of fluences were observed. Optical transparency of these samples was found to depend on implantation, irradiation, and combined processes. Correlating the structural information with surface morphology experiments, the existence of a waveguide layer on lithium niobate surface has been ascertained.