Coherent control of superradiance from nitrogen ions pumped with femtosecond pulses

TL;DR

This paper demonstrates the coherent control of superradiance from nitrogen ions in air using femtosecond laser pulses, revealing the role of macroscopic coherence and enabling potential applications in remote sensing.

Contribution

It introduces a method to control nitrogen ion superradiance with resonant seeding pulses and uncovers the temporal dynamics of macroscopic coherence in air lasing.

Findings

Superradiance can be modulated by seeding pulse delay.

Macroscopic coherence lasts about 10 picoseconds.

Control of air lasing is achieved through femtosecond pulse manipulation.

Abstract

Singly ionized nitrogen molecules in ambient air pumped by near-infrared femtosecond laser give rise to superradiant emission. Here we demonstrate coherent control of this superradiance by injecting a pair of resonant seeding pulses inside the nitrogen gas plasma. Strong modulation of the 391.4 nm superradiance with a period of 1.3 fs is observed when the delay between the two seeding pulses are finely tuned, pinpointing the essential role of macroscopic coherence in this lasing process. Based on this time-resolved method, the complex temporal evolution of the macroscopic coherence between two involved energy levels has been experimentally revealed, which is found to last for around 10 picoseconds in the low gas pressure range. These observations provide a new level of control on the "air lasing" based on nitrogen ions, which can find potential applications in optical remote sensing.