The envelope Hamiltonian for electron interaction with ultrashort pulses

Abstract

For ultrashort VUV pulses with a pulse length comparable to the orbital time of the bound electrons they couple to, we propose a simplified envelope Hamiltonian. It is based on the Kramers-Henneberger representation in connection with a Floquet expansion of the strong-field dynamics but keeps the time dependence of the pulse envelope explicit. Thereby, the envelope Hamiltonian captures the essence of the physics-light-induced shifts of bound states, single-photon absorption, and nonadiabatic electronic transitions. It delivers quantitatively accurate ionization dynamics and allows for a physical insight into the processes occurring. Its minimal requirements for construction in terms of laser parameters make it ideally suited for a large class of atomic and molecular problems.

Spatiotemporal interference of photoelectron wave packets and the time scale of nonadiabatic transitions in the high-frequency regime

“…It was found in our previous work that the yield as a function of a pulse duration has a maximum at a certain pulse duration [6]. We find a formula to predict the peak position and show that the yield becomes maximum when the pulse duration is close to a time scale of an electron.…”

“…Under such circumstances, we developed the envelope Hamiltonian to treat the photoionization dynamics in the high-frequency regime in our previous work [6]. Photoelectron amplitudes were analytically derived in the framework of the adiabatic approximation based on the envelope Hamiltonian.…”

“…Thus we also obtain the photoelectron amplitudes for a nonadiabatic transition induced by the timedependent envelope function which does not show up in the original HFFT. The capability of the envelope Hamiltonian and the adiabatic approximation was demonstrated in [6] utilizing a simple model in one dimension in the stabilization regime. It was shown that the results obtained by the full time-dependent Schrödinger equation (TDSE) calculations were accurately reconstructed by the TDSE for the envelope Hamiltonian.…”

“…II, we introduce our theoretical methods. We briefly summarize the formulations in [6] for a case of one dimension to refer to them later. In Secs.…”

Universal pulse dependence of the low-energy structure in strong-field ionization

“…(3) the time dependence of the vector potential which underscores the universal dynamical validity of the very simple soft-recollision picture. We obtain an analytical expression for (3) by taking the vector potential as the derivative of the quiver amplitude with Gaussian envelope [22]:…”