Search for nearly massless, weakly coupled particles by optical techniques.

We have searched for light scalar and/or pseudoscalar particles that couple to two photons by studying the propagation of a laser beam ($\ensuremath{\lambda}=514$ nm) through a transverse magnetic field. A limit of 3.5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}10}$ rad was set on a possible optical rotation of the beam polarization for an effective path length of 2.2 km in a 3.25 T magnetic field. We find that the coupling ${g}_{\ensuremath{\alpha}\ensuremath{\gamma}\ensuremath{\gamma}}l3.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$ Ge${\mathrm{V}}^{\ensuremath{-}1}$ at the 95% confidence level, provided ${m}_{a}l{10}^{\ensuremath{-}3}$ eV. Similar limits can be set from the absence of ellipticity in the transmitted beam. We also searched for photon regeneration in a magnetic field and found the limit ${g}_{\ensuremath{\alpha}\ensuremath{\gamma}\ensuremath{\gamma}}l6.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$ Ge${\mathrm{V}}^{\ensuremath{-}1}$ for the same range of particle mass.