Casimir energy between a plane and a sphere in electromagnetic vacuum
  The Casimir energy is computed in the geometry of interest for the most precise experiments, a plane and a sphere in electromagnetic vacuum. The scattering formula is developed on adapted plane-waves and multipole basis, leading to an expression valid for arbitrary relative values of the sphere radius and inter-plate distance. In the limiting case of perfect reflection, the electromagnetic result is found to depart from the commonly used proximity-force approximation (PFA) significantly more rapidly than expected from scalar computations. 
Paulo A. Maia Neto, Astrid Lambrecht and Serge Reynaud