Fig. 3. Principle of spatially separated electron holography.

(A) The initial energy distribution of the electron beam is a function of energy that is singly peaked at E = E₀ (right). Interaction with the reference field produces coherent superposition states with energies E = E₀ ± nℏω. The ensuing interaction with an SPP depends on the relative phase between SPP and reference fields, which results in a position-dependent electron energy distribution. The elastic part of the electron spectrum is then used to form the 2D hologram. The spectra on the right are simulations from an analytical model (see Materials and Methods). (B) Hybrid energy-space map (spectrogram) of the electrons after interaction with the two fields, as schematized in (A). (C) Spatial profiles of the normalized intensity for elastic (blue curve) and inelastic (red curve) electrons, as obtained from (B) by energy-averaging from −1 to 1 eV for the elastic contribution and from −27 to −12 eV for the inelastic one. (D) Energy profiles at the maximum and minimum of the spatial modulation shown in (B), averaged over four periods.