Recollision-Induced Superradiance of Ionized Nitrogen Molecules

Abstract

We propose a new mechanism to explain the origin of optical gain in the transitions between the excited and ground states of the ionized nitrogen molecule following irradiation of neutral nitrogen molecules with an intense ultrashort 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 superradiant emission, a feature that we confirm experimentally.

Recent Advances in Air Lasing: A Perspective from Quantum Coherence

“…One can see that the built‐up delay and the pulse duration are inversely proportional to the gas pressure p , while the peak power scales up quadratically with p . This confirms that the 391.4‐nm radiation is of the nature of superradiance …”

“…Based on the fact that a picosecond‐delayed external seed is significantly amplified for both the co‐propagation and counter‐propagation cases of the pump and seed pulses, this kind of lasing action is attributed to the seed amplification in N ions with the population inversion . Some scenarios have been proposed to explain its ultrafast gain, including the collisional excitation of rescattering electrons, multiple‐states couplings, the alignment‐induced transient inversion, etc. For details of this specific subject, one can refer to a recent review .…”

Optical gain in rotationally excited nitrogen molecular ions

“…Indeed, it is counterintuitive that strong-field ionization of the nitrogen molecule appears to preferentially create a molecular ion in the upper, not the lower, emission state. Several alternative gain scenarios have been recently suggested [9][10][11]. The lack of understanding of the gain mechanism hinders the optimization of the lasing process that could lead to the unseeded lasing in the backward direction, which would be of the most practical significance.…”

Spectroscopic analysis of high electric field enhanced ionization in laser filaments in air for corona guiding

“…During femtosecond laser FIL in air, many nonlinear effects occur simultaneously, such as intensity clamping, molecular alignment, harmonic generation, self-phase modulation and so on [3][4][5] . These complex and interesting nonlinear phenomena accompanying femtosecond laser FIL lead to promising applications in different fields, such as remote sensing [6,7] , few-cycle pulse compression [8] , atmospheric condensation and precipitation [9][10][11] , secondary light source generation ranging from air lasing to terahertz emission [12][13][14][15][16][17][18] , and triggering and guiding high-voltage discharge with possible applications in lightning control [19][20][21][22][23][24] .…”