The refractive index of ion implanted diamond

Knowledge of the refractive index of diamond as a function of the number of lattice defects is required to evaluate the potential of ion beam lithography for realisation of a photonic crystal in single crystal diamond. Diamond undergoes a pronounced physical transformation when subjected to bombardment by high energy ions. Sufficiently high fluences produce a visible darkening of the crystal suggesting significant changes to the index of refraction. This suggests diamond-based photonic devices could be fabricated by ion beam lithography. We investigate the refractive index of diamond after ion implantation with a focused ion beam. We have measured the refractive index for varying ion fluences over many orders of magnitude for gallium and hydrogen ion irradiation. Measurements are performed using ellipsometry over a wide spectral range; from UV to near IR. We have found that the refractive index behaves differently above and below the critical amorphization threshold of diamond.