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Correct determination of layer thicknesses on a subnanometer scale is crucial for studies of giant magnetoresistance, magneto-optical (MO) Kerr rotation, magnetic interlayer coupling, and other magnetic properties of metallic multilayers. Some structures such as [Co/Ni] and [Co/Pt] with fewer than 20 repeats are difficult to be analyzed by x-ray diffraction (XRD) due to too little material. In this work, in-situ spectroscopic ellipsometry (in-situ SE) is used to precisely determine the optical constants undisturbed by oxidation, and the growth rates of different metal films deposited in a sputtering chamber. In-situ SE determines both the constant and continuously changing growth rates during deposition of individual layers. SE data were also taken during multilayer thin-film growth, from which we determine the individual layer thicknesses in the superlattice to a fraction of an angstrom. The in-situ SE data and ellipsometric analysis of [Co/Au] and [Co/Ni] multilayers on thick gold-coated silicon, and [Co/Pt] multilayers with a Pt underlayer are presented. Less than a few percent difference was found by comparing the XRD thickness results to thein-situ SE thickness results. In-situ SE permits studies of oxidation kinetics, important because oxidation strongly influences both the magnetic and MO results. Specifically, spectroscopic MO Kerr rotation, ellipticity, and figure of merit of [Co/Ni] and [Co/Pt] multilayers with different repeat structures, with and without capping layers are reported covering the spectral range from ultraviolet to near infrared.