Intense, directional UV emission from molecular nitrogen ions in an adaptively controlled femtosecond filament

Abstract

Abstract. Using phase-shaped millijoule 1030-nm femtosecond pulses generating a filament in a cell filled with N 2 , we obtain intense forward UV emission between vibrational manifolds of B 2 Σ and X 2 Σ states of N 2 + for optimal pulse sequences. The effect is tentatively ascribed to wave-mixing between intense NIR pulses and weak supercontinuum components, resonant to the UV transitions, whereby a noninstantaneous nonlinear susceptibility is linked to rotational coherence in ions.

Real-time observation of dynamics in rotational molecular wave packets by use of air-laser spectroscopy

“…It is noteworthy that although the existence of population inversion has been confirmed with systematic experimental investigations, the mechanism behind the establishment of the inverted population within an ultra-short period of only ~100 fs is still under hot debate. In fact, several models have been proposed to understand the physics of such air laser, including stimulated emission based on seed amplification in a population inverted system, four-wave mixing, and seed-triggered superradiance [17][18][19][20]. Nevertheless, none of these models has been completely confirmed and widely accepted.…”

Recent Advances in Air Lasing: A Perspective from Quantum Coherence

“…Molecular nitrogen ion (N) lasing is the third type of air lasing, which originates from the transition from the excited state to the ground state . Lasing actions from N ions have been experimentally observed by several research groups since the first report in 2011 . Besides its promising application in the remote sensing similar to the other two types of air lasing, the understanding of the physical procedure in N lasing is also attracting great interests.…”

“…Lasing actions from N + 2 ions have been experimentally observed by several research groups since the first report in 2011. [22,25,[27][28][29][30][66][67][68][69][70][71][72][73][74][75][76][77] Besides its promising application in the remote sensing similar to the other two types of air lasing, the understanding of the physical procedure in N + 2 lasing is also attracting great interests. Moreover, the generation of N + 2 lasing is the result of a complex interaction between strong laser fields and nitrogen molecules.…”

“…[86][87][88][89][90][91] On the other hand, the understanding of the gain mechanism in N + 2 lasing is highly desired in the strongfield-ionization framework, which has motivated many tentative and interesting explanations. [66,69,72,74,76,83,[86][87][88][89][90][91][92][93][94][95][96][97][98][99] Up to now, it is still lack of a complete physical picture to explain all key experimental observations on N + 2 lasing. Thus, the exploration of the underlying origin of the ultrafast gain in the strong-field ionized molecules is of significant importance for understanding the fundamental physics in the interaction between the strong laser field and molecules.…”

Coupling ofN2+rotational states in an air laser from tunnel-ionized nitrogen molecules

“…Several models have been proposed to interpret the physics of such air lasers, including stimulated emission based on seed amplification in a population-inverted system, four-wave mixing, and seedtriggered super-radiance, etc. [11][12][13][14][15]. In particular, Kartashov et al recently proposed that the different rotational periods of aligned molecular ions on the ground and excited electronic states can lead to transient laser gain and thus the creation of bright narrow-bandwidth coherent UV emissions in suitable time windows [15].…”