In the present work, Rutherford backscattering spectroscopy (RBS) measurements, scanning electron microscopy, and optical characterization are carried out on porous silicon (PS) multilayer interference filters in order to determine their compositional profile, homogeneity, and overall optical behavior. In addition, RBS measurements allow determination of the porosity profile of multilayer structures. Thus, both porosity and oxidation degree are determined for each individual layer forming the stack, giving a straightforward measure of the in-depth homogeneity of these structures. Finally, the aging effects on the optical behavior and compositional profile of the PS stacks are studied by comparing as-prepared and aged multilayers. The results reveal good in-depth homogeneity of the PS multilayers and an oxygen enrichment with ambient air exposure, which results in a lowering of the effective refractive index and a blueshift of the reflectance spectra of the filters. (c) 2005 The Electrochemical Society.