The setup consists of a sensitive ellipsometer attempting to detect the small changes in the polarization state of light propagating through a 1 m long magnetic field region in vacuum. It is based on a high finesse Fabry-Perot cavity and a superconducting 5 T rotating dipole magnet. Indeed, vacuum will become birefringent in the presence of a strong magnetic field. A possible secondary effect, which could mask the vacuum magnetic birefringence, could be due to the existence of a light, neutral pseudoscalar/scalar particle coupling to two photons via the Primakoff effect.