Manipulating Parallel and Perpendicular Multiphoton Transitions in H_{2} Molecules

Non vertical ionization-dissociation model for strong IR induced dissociation dynamics of [Formula: see text]

Electron-nuclear coupling plays a crucial role in strong laser induced molecular dissociation dynamics. The interplay between electronic and nuclear degrees of freedom determines the pathways and outcomes of molecular fragmentation. However, a full quantum mechanical treatment of electron-nuclear dynamics is computationally intensive. In this work, we have developed a Strong Laser Induced non-adiabatic Multi-Ionic-Multi-Electric States (SLIMIMES) approach, which contains the electron-laser and electron-nuclear couplings. We validate our model using a showcase example: water dissociation under strong infrared (IR) laser pulses. Our investigation reveals the predominant role of a non-vertical dissociation pathway in the photo-ionization dissociation (PID) process of [Formula: see text]. This pathway originates from neutral [Formula: see text], which undergoes vertical multi-photon-single-ionization, reaching the intermediate dissociation states of [Formula: see text] within [Formula: see text]. Subsequently, [Formula: see text] dissociates into [Formula: see text], with both [Formula: see text] and [Formula: see text] fragments potentially ionizing an electron during interaction with the IR laser. This sequential PID pathway significantly contributes to the dissociation yields of water dication. Our calculations are consistent with recent experimental data, which focus on measuring the branching ratio of water dication dissociation. We aim for our model to provide a deeper understanding and a fresh perspective on the coupling between electron and nuclear dynamics induced by a strong IR laser field.

Excitation dynamics in molecule resolved by internuclear distance driven by the strong laser field

Rydberg-state excitation of stretched model molecules subjected to near-infrared intense laser fields has been investigated based on a fully quantum model (QM) proposed recently and the numerical solutions of time-dependent Schrödinger equation (TDSE). Given the good agreement between QM and TDSE, it is found that, as the molecules are stretched, the electron tends to be trapped into low-lying Rydberg-states after its ionization from the core, which can be attributed to the shift of the ionization moments corresponding to maximum excitation populations. Moreover, the n-distribution is broadened for molecules with increasing internuclear distance, which results from the change of momentum distribution of emitted electrons. Analysis indicates that both of the above phenomena are closely related to the interference effect of electronic wave packets emitted from different nuclei. Our study provides a more comprehensive understanding of the molecular excitation in intense laser fields, as well as a means of possible applications to related experimental observations.

Femtosecond Polarization Shaping of Free-Electron Laser Pulses

We demonstrate the generation of extreme-ultraviolet (XUV) free-electron laser (FEL) pulses with time-dependent polarization. To achieve polarization modulation on a femtosecond timescale, we combine two mutually delayed counterrotating circularly polarized subpulses from two cross-polarized undulators. The polarization profile of the pulses is probed by angle-resolved photoemission and above-threshold ionization of helium; the results agree with solutions of the time-dependent Schrödinger equation. The stability limit of the scheme is mainly set by electron-beam energy fluctuations, however, at a level that will not compromise experiments in the XUV. Our results demonstrate the potential to improve the resolution and element selectivity of methods based on polarization shaping and may lead to the development of new coherent control schemes for probing and manipulating core electrons in matter.