Imaging Surface Plasmons: From Leaky Waves to Far-Field Radiation

We show that, contrary to the common wisdom, surface plasmon poles are not involved in the imaging process in leakage radiation microscopy. Identifying the leakage radiation modes directly from a transverse magnetic potential leads us to reconsider the surface plasmon field and unfold the non-plasmonic contribution to the image formation. While both contributions interfere in the imaging process, our analysis reveals that the reassessed plasmonic field embodies a pole mathematically similar to the usual surface plasmon pole. This removes a long-standing ambiguity associated with plasmonic signals in leakage radiation microscopy.