  Electron energy-loss spectroscopy (EELS) performed in transmission electron
microscopes is shown to directly render the photonic local density of states
(LDOS) with unprecedented spatial resolution, currently below the nanometer.
Two special cases are discussed in detail: (i) 2D photonic structures with the
electrons moving along the translational axis of symmetry and (ii) quasi-planar
plasmonic structures under normal incidence. Nanophotonics in general and
plasmonics in particular should benefit from these results connecting the
unmatched spatial resolution of EELS with its ability to probe basic optical
properties like the photonic LDOS.
