Single crystal GaAs substrates implanted with high-energy 56Fe ions were optically investigated before and after annealing, over the photon energy range 0.1–1.4eV. The spatial distribution of the damage was probed by etching the sample and showed that defect density peaks at a depth of about 10μm. Annealing studies showed that the mid gap defect states were annealed out more rapidly than the near band edge defect states during annealing up to 350C whereas the near band edge defect states were annealed out more rapidly than mid gap defect states during annealing between 350–600C. The fringe patterns observed in the transmission spectra were analyzed to investigate quantitatively changes in the refractive index of the radiation-damaged region. Kramers–Kronig relation was used to correlate the absorption due to damage with changes in the refractive index. The results showed that the high-energy ion-implanted layer contained amorphous pockets.Distribution of Radiation Induced Defects and Modification of Optical Constants of GaAs Implanted with High-Energy 56Fe Ions. M.M.Belekar, A.M.Narsale, B.M.Arora, K.V.Sukhatankar, S.K.Dubey, V.P.Salvi: Nuclear Instruments and Methods in Physics Research Section B, 2004, 226[3], 301-8