The results of bench tests performed on a new method of combined interferometry/polarimetry for the magnetic-field reconstruction of tokamak plasmas is presented. In particular, the sensitivity obtained in the polarimetric measurement shows the feasibility of Faraday rotation determination approaching a precision of +/-0.2 degrees. The method is based on an optically pumped far-infrared laser with a rotating polarization where both the interferometric and polarimetric information is determined from phase measurements. Specific sources that introduce disturbances in the optical arrangement and that can limit the attainment of the polarimetric precision, mentioned above, are discussed. (C) 1997 American Institute of Physics.