Multiple-Photon Resonance Enabled Quantum Interference in Emission Spectroscopy of N_2^+

TL;DR

This paper demonstrates quantum interference driven by multiple photons in nitrogen ion emission spectroscopy, revealing Fano resonance and free-induction decay, thus advancing understanding of laser-matter interactions near multiple photon resonance.

Contribution

It introduces the observation of multi-photon driven quantum interference effects in nitrogen ions, expanding the understanding beyond single-photon resonance phenomena.

Findings

Fano resonance observed in emission spectrum

Dynamic Stark effect creates a continuum

Time-resolved emission reveals free-induction decay

Abstract

Quantum interference occurs frequently in the interaction of laser radiation with materials, leading to a series of fascinating effects such as lasing without inversion, electromagnetically induced transparency, Fano resonance, etc. Such quantum interference effects are mostly enabled by single-photon resonance with transitions in the matter, regardless of how many optical frequencies are involved. Here, we demonstrate quantum interference driven by multiple photons in the emission spectroscopy of nitrogen ions that are resonantly pumped by ultrafast infrared laser pulses. In the spectral domain, Fano resonance is observed in the emission spectrum, where a laser-assisted dynamic Stark effect creates the continuum. In the time domain, the fast-evolving emission is measured, revealing the nature of free-induction decay (FID) arising from quantum radiation and molecular cooperativity. These findings clarify the mechanism of coherent emission of nitrogen ions pumped with MIR pump laser and are likely to be universal. The present work opens a route to explore the important role of quantum interference during the interaction of intense laser pulses with materials near multiple photon resonance.