Energy-resolved coherent diffraction from laser-driven electronic motion in atoms

Abstract

We investigate theoretically the use of energy-resolved ultrafast electron diffraction to image laserdriven electronic motion in atoms. A chirped laser pulse is used to transfer the valence electron of the lithium atom from the ground state to the first excited state. During this process the electronic motion is imaged by 100-fs and 1-fs electron pulses in energy-resolved diffraction measurements. Simulations show that the angle-resolved spectra reveal the time evolution of the energy content and symmetry of the electronic state. The time-dependent diffraction patterns are further interpreted in terms of the momentum transfer. For the case of incident 1-fs electron pulses, the rapid 2s-2p quantum beat motion of the target electron is imaged as a time-dependent asymmetric oscillation of the diffraction pattern.

Time-resolved electron(e,2e)momentum spectroscopy: Application to laser-driven electron population transfer in atoms

“…[47,54], for the purpose of completeness we reproduce the main features of those results here. Figure 3 …”

“…Since we have presented a detailed theoretical derivation and analysis in Ref. [54], we emphasize here the changes and additional approximations that are necessary to generalize the conventional EMS theory to the time-dependent case.…”

“…As many details of our simulations have been discussed in the context of ultrafast electron diffraction [47,54], we focus on those aspects that are unique to the (e,2e) process and only summarize briefly our numerical procedures. Since the lithium electronic state ψ 1 (t) is written in terms of its eigenstates [see Eq.…”

“…The first needed modification is to generalize the transition amplitude T mn for the case of a system having a time-dependent Hamiltonian [54][55][56]. Since the Born approximation remains valid, the effects of the projectile-target interaction on the entrance wave function can be neglected.…”

“…However, in the case of laser-driven population transfer in lithium atoms, the scattering system is influenced by the external laser electromagnetic field, and hence the lithium target electronic state cannot be described simply as a coherent superposition state. In our previous works [47,54], we have developed a time-dependent distorted-wave approximation to simulate the diffraction of ultrafast electrons from laser-driven scattering target systems. This approximation fully accounts for the interaction between the laser and the scattering target system (in the electric dipole approximation) such that the dressing of the wave function of the incident electron and the population transfer in the lithium atoms can be accurately described, while the target-projectile interaction is modeled as a perturbation.…”