In this work, in situ spectroscopic ellipsometry (in situ SE) is used to determine precisely the optical constants undisturbed by oxidation, and the growth rates of different metal and dielectric films deposited by sputtering. In situ SE determines both the constant, and potentially changing growth rates during deposition of individual layers. The SE data were also taken during growth of metallic multilayers, from which we determine the individual layer thicknesses to a fraction of an Angstrom. The in situ and ex situ ellipsometric analysis of a [Co/Au] multilayer on thick gold coated silicon, [Co/Pt] multilayers with a Pt underlayer, and SIC cladded TbFeCo layers are presented. Less than a few percent difference in multilayer period thickness was found by comparing low angle X-ray diffraction results to the in situ SE results. In situ SE also permitted studies of oxidation kinetics, which are important because oxidation in ultra thin films can strongly influence properties and performance of devices made with ultra thin multilayers. This research is especially relevant to the data storage industry, where control of ultra thin metallic layers is critical to reproducible manufacture of both read-write heads and recording media.