Generation of bright laser-like coherent emissions from nitrogen molecular ions in intense infrared laser fields: A unique quantum system for extreme nonlinear optics

TL;DR

This paper investigates the generation of multiple narrow-bandwidth laser-like emissions from nitrogen molecular ions in intense infrared laser fields, revealing nonlinear processes like four-wave mixing and stimulated Raman scattering enhanced at resonant wavelengths.

Contribution

It demonstrates a novel mechanism for generating coherent emissions from nitrogen ions via nonlinear optical processes in intense mid-infrared laser fields.

Findings

Multiple coherent emission lines are generated from nitrogen ions.

Nonlinear processes are enhanced at resonant wavelengths.

High conversion efficiencies are achieved from pump laser to emissions.

Abstract

We report on an investigation of simultaneous generation of several narrow-bandwidth laser-like coherent emissions from nitrogen molecular ions ( ) produced in intense mid-infrared laser fields. With systematic examinations on the dependences of coherent emissions on gas pressure as well as several laser parameters including laser intensity, polarization and wavelength of the pump laser pulses, we reveal that the multiple coherent emission lines generated in originate from a series of nonlinear processes beginning with four-wave mixing, followed with stimulated Raman scattering. Our analyses further show that the observed nonlinear processes are greatly enhanced at the resonant wavelengths, giving rise to high conversion efficiencies from the infrared pump laser pulses to the coherent emission lines near the transition wavelengths between the different vibrational energy levels of ground X and that of the excited B states.