Electron-Light Interactions Beyond Adiabatic Approximation

Abstract

Aligned with the technological developments of electron-based characterization techniques, our theoretical frameworks are yet to be adapted to the strong-laser and slow-electron regimes. More specifically, there exist certain domains where our adiabatic approximations might break down. This is practically important from several viewpoints: (i) in PPM, the shape and amplitude of electron beams are both strongly manipulated, in addition to their phase; (ii) even in free-space electron-light interactions, purely elastic approximations might appear to be a mere over-simplification (Kozak et al. in Nat Phys Lett, 2017 [1]); (iii) during the interaction of electron beams with gratings and light, electron bunching appears to be an additional mechanism to the electron acceleration, where both the acceleration and bunching mechanisms are controlled by the longitudinal broadening of the electron beam relative to the grating period (Talebi in New J Phys 18:123006, 2016 [2]); and (iv) shaped electron beams interacting with matter have different selection rules and might offer approaches for manipulating the electron-induced radiations (Sergeeva et al. in Opt Express 25:26310–26328, 2017 [3]; Tsesses et al. in Phys Rev A 95:013832, 2017 [4]; Kaminer et al. in Phys Rev X 6:011006, 2016 [5]). The last point is fundamentally important, as even for a single electron wave packet, when the electron beam is in a superposition of at least two momentum states, interferences between different quantum paths in the interaction of photons with the electron may occur (Peatross et al. in Phys Rev Lett 100:153601, 2008 [6]). As noted by Keitel and co-workers, the quantum eigenstates of electrons in a nonplanar laser beam or in general shaped light waves are unknown (Peatross et al. in Phys Rev Lett 100:153601, 2008 [6]). For this reason, the development of self-consistent numerical methods may facilitate a better understanding of the outcomes of experiments (Talebi in New J Phys 18:123006, 2016 [2]; White et al. in Phys Rev B 86:205324, 2012 [7]; Kohn et al. in Phys Rev 140:1133, 1965 [8]) and stimulate the design of new experiments.

Portions of the text of this chapter have been re-published with permission from [9], re-printed under the CC BY license; [10], re-printed under the CC BY license.