Recollision induced superradiance of ionized nitrogen molecules

TL;DR

This paper introduces a novel mechanism where multiple recollisions induced by intense ultrashort laser pulses cause superradiant emission in ionized nitrogen molecules, explaining optical gain in excited states.

Contribution

It presents a new recollision-based excitation mechanism leading to superradiance in ionized nitrogen, supported by experimental confirmation.

Findings

Recollision mechanism causes population transfer to excited states.

Superradiant emission observed experimentally.

Optical gain explained by the proposed mechanism.

Abstract

We propose a new mechanism to explain the origin of optical gain in the transitions between excited and ground state of the ionized nitrogen molecule following irradiation of neutral nitrogen molecules with an intense ultra short laser pulse. An efficient transfer of population to the excited state is achieved via field-induced multiple recollisions. We show that the proposed excitation mechanism must lead to a super-radiant emission, a feature that we confirm experimentally.