Two materials, calcium fluoride and titanium dioxide, are used for this study of film growth. Ellipsometry measurements have been performed in situ on TiO2 films at fixed wavelength lambda during deposition, and on very thin CaF2 films at fixed lambda or vs. lambda at different deposition steps. The value of the index of refraction n depends strongly on the nature and the temperature of the substrate and on the thickness of the deposit. For CaF2 films deposited on Si wafers covered with their native oxide, a model including an interfacial layer, which takes into account the interaction of the film with the Si substrate, is proposed for reproducing the ellipsometric data. For CaF2 films deposited on thick thermal SiO2, no evidence for chemical interaction has been found. For TiO2 films, it is shown that, even under a drastic control of the deposition parameters, reproducible samples are difficult to obtain with classical evaporation methods. The inhomogeneity of the index of refraction of TiO2 films is well described by a main "bulk" layer covered by a thin overlayer with a lower refractive index. The ellipsometry measurements correlate rather well with atomic force microscopy measurements. The influence of atmospheric moisture has been checked on TiO2 films.