Fig. 6: Electron energy dependence of the electron-near-field coupling strength.
From: Spontaneous and stimulated electron–photon interactions in nanoscale plasmonic near fields
BEM calculation of the laser-induced electron-near-field coupling strength \(\left| \beta \right|^2\) as a function of the along-the-beam wave vector \(q = \omega /v\) and impact parameter d relative to the tip apex. Data are obtained for a fixed photon energy of \(\hbar \omega\)=1.73 eV matching the tip resonance energy and for varying electron energies E0 (see top axis). Other excitation parameters are identical to those in Figs. 4c and 5d. The inset shows a profile along the white dashed line for d = 3 nm, representing the local spatial Fourier composition of the optical field along the electron trajectory. For a given E0, the electron can only couple to the Fourier field component with a spatial phase advance q, affecting both the amplitude and the spatial distribution of \(\left| \beta \right|^2\)
