Controlling quantum wave packet of electronic motion on field‐dressed Coulomb potential of by carrier‐envelope phase‐dependent strong field laser pulses

Abstract

Solving numerically a non‐Born‐Oppenheimer time‐dependent Schrödinger equation to study the dynamics of H2 subjected to strong field six‐cycle laser pulses (I=4×1014 W/cm2, λ=800 nm) leads to the newly ultrafast electron imaging in the dissociative‐ionization of H2+. This includes the electron distribution in H2+ oscillates symmetrically with laser cycle with ϑ+π periodicity where the distribution concentrates between two protons for about 8 fs, being trapped in a Coulomb potential well. Nonetheless, the most important finding reveals that the electron symmetrical distribution begins to break up in the field‐free region after 24 fs when the H2+ internuclear distance stretches larger than 9 a.u. It is a result of the distortion of Coulomb potential where the ejected electron preferentially localizes in one of the double‐well potential separated by the inner Coulomb potential barrier, leading to the new images of charge resonance enhanced ionization. Controlling laser carrier‐envelope phase ϑ enables one to quantify such phenomena with the highest total asymmetries Aetot of 0.75 and −0.75 occur at 10° and 190°, respectively, associated with the electron preferential directionality being ionized to the right and the left paths along the H2+ molecular axis.

Efficient Control of Electron Localization and Probability Modulation with Synthesized Two-Color Intense Laser Pulses

“…From the theoretical perspective, the study of laser-induced photofragments of the HD + molecular ion is, certainly, more complex than the homonuclear counterparts, normalH 2 + and normalD 2 + , due to the inherent electric dipole moment induced by the difference in nuclear mass. On the other hand, from the numerical point-of-view, to aptly explicate several experiments using intense electric fields for atoms and molecules, performing exact quantum dynamics ,,− appears to be the most accurate and precise way out. However, solving the time-dependent Schrödinger equation (TDSE) turns out to be quite expensive computationally due to the necessity of simultaneous inclusion of both electronic and nuclear coordinates for accounting for the strong coupling of both degrees-of-freedoms, − whereas the obstacles of such computational cost could somewhat be overcome with classical dynamical methods as can be found elsewhere, ,,− which are based on quasi-classical trajectory − or semiclassical theoretical models. , …”

Strong Laser Field-Driven Coupled Electron–Nuclear Dynamics: Quantum vs Classical Description

“…On a different note, Roudnev and Esry, in their theoretical study, proposed that CEP effects arise because of the superposition of electronic states with different parities, which, in turn, indicates that the CEP dependence is a quantum mechanical phenomenon. Understanding of such CEP-dependent coupled dynamics needs a fully quantum mechanical treatment , and requires the observation of both electronic and nuclear wave packet dynamics, simultaneously. − Indeed, during the interaction of a strong laser field, the dissociation and ionization phenomena occur concurrently , by following different pathways, where several control schemes were proposed to control as well as explain the electron localization phenomena. ,,, Due to this nonseparability of coupled electronic and nuclear degrees of freedom, − the solution of the time-dependent Schrödinger equation (TDSE) becomes extremely expensive, even for a one-electron system, for example, H 2 + , which requires propagation of both electronic and nuclear wave packets altogether. ,− To overcome the huge computational cost in quantum dynamics, alternate and computationally less-expensive methods based on classical mechanics had also been proposed in recent years, which have been able to successfully interpret several strong field experiments for atoms and molecules. ,− In the recent past, quasi-classical trajectory-based models − were employed to study the molecular double-ionization phenomena of molecules under the influence of intense laser fields, and also, some semiclassical theoretical methods , were used for studying electron collision–recollision dynamics and generation of higher order harmonics. Apart from the advantage in computational efficiency, trajectory-based classical models provide relatively easy interpretation of the observable by the back analysis of individual trajectories.…”