In situ optical reflectometry at 670 nm is used to monitor the pulsed laser deposition of thin films and multilayers of copper and cobalt. By comparing measured reflectivity with a Fresnel calculation, which includes a Bruggemann description of the dielectric function for partially dense material, the nature of the early stages of the deposition of copper on cobalt can be discerned. It seems that the deposition begins with the nucleation of a partially dense layer, and the formation of fully dense material commences after a deposition corresponding to about 0.3 nm of Cu. Thereafter the thickness of the fully dense layer increases while a partially dense surface layer is maintained. The experiment demonstrates that optical reflectometry can be an effective thickness monitor for the deposition of ultrathin metal films and multilayers and also yields some new information on the nature of the growth.