Sub-cycle coherent control of ionic dynamics via transient ionization injection

TL;DR

This study reveals that transient ionization in intense laser fields causes nitrogen molecular ions to be predominantly excited rather than in the ground state, challenging traditional tunneling theory and impacting molecular ion dynamics.

Contribution

It introduces a quantum open-system approach to model ionization dynamics, highlighting the role of transient ionization injection and strong electronic couplings in molecular ion excitation.

Findings

Nitrogen molecular ions are mainly in excited states due to transient ionization effects.

Vibrational distributions deviate from Franck-Condon predictions.

Mechanisms support nitrogen molecular ion lasing and are likely universal.

Abstract

We investigate the interwoven dynamic evolutions of neutral nitrogen molecules together with nitrogen ions created through transient tunnel ionization in an intense laser field. By treating the molecules as open quantum systems, it is found that considering real-time injection of ions and strong couplings among their electronic states, nitrogen molecular ions are primarily populated in the electronically excited states, rather than staying in the ground state as predicted by the well-known tunneling theory. The unexpected result is attributed to sub-cycle switch-on of time-dependent polarization by transient ionization and dynamic Stark shift mediated near-resonant multiphoton transitions. Their combined contribution also causes that the vibrational distribution of N$_2^+$ does not comply with Franck-Condon principle. These findings corroborate the mechanism of nitrogen molecular ion lasing and are likely to be universal. The present work opens a new route to explore the important role of transient ionization injection in strong-field induced non-equilibrium dynamics.