XUV lasing during strong-field assisted transient absorption in molecules

TL;DR

This paper demonstrates XUV lasing in molecules through IR-assisted amplification involving Rydberg states, using ab-initio simulations of the hydrogen molecular ion, revealing conditions for gain and lasing in strongly driven molecules.

Contribution

It introduces a novel mechanism for XUV lasing in molecules via IR-assisted Rydberg state amplification, supported by ab-initio non-Born-Oppenheimer simulations.

Findings

XUV amplification occurs via IR-assisted Rydberg states in molecules.

High IR intensities can make molecules quasi-transparent for XUV, enabling gain.

Lasing can be achieved even from initially unexcited molecules at higher IR intensities.

Abstract

Using ab-initio non-Born-Oppenheimer simulations, we demonstrate amplification of XUV radiation in a high-harmonic generation type process using the example of the hydrogen molecular ion. A small fraction of the molecules is pumped to a dissociative Rydberg state from which IR-assisted XUV amplification is observed. We show that starting at sufficiently high IR driving field intensities the ground state molecules become quasi-transparent for XUV radiation, while due to stabilization gain from Rydberg states is maintained, thus leading to lasing from strongly driven Rydberg states. Further increase of the IR intensity even leads to gain by initially unexcited molecules, which are quickly excited by the driving IR pulse.