An analysis was carried out of SOI/SIMOX structures obtained by sequential implantation and annealing (SIA). The analysis of these structures has been made in relation to those obtained by an equivalent standard single implant and anneal (SS structures), by means of infrared reflection spectroscopy. The use of a fast Fourier transform infrared (FTIR) system allows the combination of a low measuring time of the spectra (on the order of several minutes) with a high spectral resolution (up to 0.02 cm^-1). Complementary optical measurements such as photoluminescence and Raman spectroscopy using different excitation powers and wavelengths reveal the higher quality of the surface region of the top silicon layer free of precipitates in the SIA material. These data, together with the FTIR results, show the potential of the SIA technique for obtaining high quality quasi-ideal SOI structures.