Nonadiabatic dynamics and multiphoton resonances in strong field molecular ionization with few cycle laser pulses

TL;DR

This study investigates how few-cycle laser pulses influence molecular ionization, revealing the significant roles of multiphoton resonances and nonadiabatic dynamics in determining ionization pathways and outcomes.

Contribution

It demonstrates that resonances and nonadiabatic effects impact ionization even with ultrashort pulses, expanding understanding of strong field molecular ionization mechanisms.

Findings

Multiphoton resonances affect ionization pathways.

Nonadiabatic dynamics influence final ionic states.

Resonance effects persist even with pulses shorter than four cycles.

Abstract

We study strong field molecular ionization using few- (four to ten) cycle laser pulses. Employing a supercontinuum light source, we are able to tune the optical laser wavelength (photon energy) over a range of about $\sim$200 nm (500 meV). We measure the photoelectron spectrum for a series of different molecules as a function of laser intensity, frequency, and bandwidth and illustrate how the ionization dynamics vary with these parameters. We find that multiphoton resonances and nonadiabatic dynamics (internal conversion) play an important role and result in ionization to different ionic continua. Interestingly, while nuclear dynamics can be "frozen" for sufficiently short laser pulses, we find that resonances strongly influence the photoelectron spectrum and final cationic state of the molecule regardless of pulse duration -- even for pulses that are less than four cycles in duration.