Surface Plasmon Microscopy Versus Optical Microscopy: Ez Dominates in SPM

Objective-coupled surface plasmon microscopy (SPM) shows extremely high similarity with conventional optical microscopy (OM) in both configuration and theoretical model. And there is a common misunderstanding in SPM that all the three polarization components Ex, Ey, and Ez of the focused beam contribute to excitation of SPs, similar as the situation in OM that all the polarization components generate image contrast. Actually, this is not the case and some literatures have suggested `only Ez excites SPs'. However, so far there has been no related theory to support this issue, and the common misunderstanding and corresponding errors are still applied in both academia and industry. The present work clarifies this significant issue for the first time. We theoretically prove that `only Ez excites SPs' and further give two related phenomena as evidences.