Analysis of electron spectra dynamics in a moving periodical ponderomotive potential

The interaction between freely propagating electrons and light waves is typically described using an approximation in which we assume that the electron velocity remains approximately the same during the interaction. In this article we analytically describe the dynamics of electrons in an interaction potential generated by an optical beat wave beyond this regime and find a structure of sharp electron distribution peaks that periodically alternate in the energy/momentum spectrum. In the classical description we analytically solve the nonlinear equation of motion, which is an analogy to the mathematical pendulum. While addressing the problem using quantum mechanics, we first use a parabolic approximation of the interaction potential and then we also study the evolution of the electron wavepacket in an infinite periodical potential. Using numerical simulations we show the classical and quantum evolution of the electron spectra during the interaction for different conditions and experimental settings.