Electronic quantum coherence induced by strong field molecular ionization

TL;DR

This paper demonstrates that strong field ionization of nitrogen molecules can generate electronic quantum coherence, revealing new possibilities for controlling molecular wavepackets in nonlinear optics.

Contribution

It provides the first experimental evidence of electronic coherence induced by strong field ionization in molecules, supported by a quantum model calculation.

Findings

Electronic coherence observed via four-wave mixing in N₂⁺ ions.

Coherence generated by strong field ionization can encompass multiple molecular states.

Experimental results match quantum model predictions.

Abstract

The existence of electronic coherence can fundamentally change the scenario of nonlinear interaction of light with quantum systems such as atoms and molecules, which, however, has escaped from observation in the investigations of strong field nonlinear optics in the past several decades. Here, we report on the generation of electronic quantum coherence by strong field ionization of nitrogen molecules in an intense 800 nm laser field. The coherence is experimentally revealed by observing a resonant four-wave mixing process in which the two pump pulses centered at 800 nm and 1580 nm wavelengths are temporally separated from each other. The experimental observation is further reproduced by calculating the nonlinear polarization response of N_2^+ ions using a three-level quantum model. Our result suggests that strong field ionization provides a unique approach to generating a fully coherent molecular wavepacket encapsulating the rotational, vibrational, and electronic states.