Different kinds of group IV heterostructures have been studied by means of spectroscopic ellipsometry (SE) and grazing X-ray reflectance (GXR). GXR was used to determine the thicknesses of the SiGe and Si layers in SiGe/Si and Si/SiGe/Si structures without ambiguity. Precise optical indices can be deduced using SE on single-layer samples. The same database is used to analyze more complex double-layer structures. SiC samples obtained by excimer laser annealing of carbon-implanted silicon have also been studied by SE. We show that the amorphous silicon profile of the samples versus the energy density used for the annealing can be accurately determined.