Li, C.L. Corbett, W.J. Xu, Y.H. Zhang, W.J. JACoW Geneva, Switzerland 978-3-95450-177-9 10.18429/JACoW-IBIC2016-MOPG71 English 241-244 MOPG71 polarization radiation extraction synchrotron synchrotron-radiation Contribution to a conference proceedings 2017 2017-02 http://dx.doi.org/10.18429/JACoW-IBIC2016-MOPG71 http://jacow.org/ibic2016/papers/mopg71.pdf Synchrotron radiation from dipole magnets is linearly polarized in the plane of acceleration and evolves toward circular polarization with increasing vertical observation angle. The intensity of the x-y field components can be modeled with Schwinger's theory for the angular-spectral power distribution. Combined with Fresnel's laws for reflection at a mirror surface, it is possible to model field polarization of visible SR light in the laboratory. The polarization can also be measured with a polarizer and quarter wave plate to yield Stokes' parameters S0-S3. In this paper we present measurements and modeling of the visible SPEAR3 SR beam in terms of Stokes' parameters and plot on the results on the Poincaré sphere.