An optical 2-beam surface stress measurement and magneto-optical Kerr-effect has been combined with a liquid helium cooled cryostat. Sample temperatures down to 30 K and magnetic fields up to 0.7 T are achieved under UHV conditions. Low temperatures are exploited to obtain the first experimental data on the surface stress change induced by the adsorption of the noble gas Xe on Pt(111). High magnetic fields and low temperatures are used to characterize the magnetic properties of Co monolayers in longitudinal and polar Kerr geometries. The effective magnetic anisotropy is extracted from hard axis magnetization loops.