Remote creation of strong and coherent emissions in air with two-color ultrafast laser pulses

TL;DR

This paper demonstrates the remote generation of strong, coherent narrow-band emissions in air at specific wavelengths using two-color ultrafast laser pulses, revealing an ultrafast population inversion mechanism in nitrogen ions.

Contribution

It introduces a novel method for remote generation of coherent emissions in air using orthogonally polarized two-color laser pulses, highlighting an ultrafast population inversion process.

Findings

Narrow-bandwidth emissions at ~391 nm and ~428 nm generated in air.

Emission durations are ~2.4 ps and ~7.8 ps, longer than pump pulses.

Evidence of an ultrafast, instantaneous population inversion mechanism.

Abstract

We experimentally demonstrate generation of strong narrow-bandwidth emissions with excellent coherent properties at ~391 nm and ~428 nm from molecular ions of nitrogen inside a femtosecond filament in air by an orthogonally polarized two-color driver field (i. e., 800 nm laser pulse and its second harmonic). The durations of the coherent emissions at 391 nm and 428 nm are measured to be ~2.4 ps and ~7.8 ps respectively, both of which are much longer than the duration of the pump and its second harmonic pulses. Furthermore, the measured temporal decay characteristics of the excited molecular systems suggest an "instantaneous" population inversion mechanism that may be achieved in molecular nitrogen ions at an ultrafast time scale comparable to the 800 nm pump pulse.