Formation Mechanism of Excited Neutral Nitrogen Molecules Pumped by Intense Femtosecond Laser Pulses

Wei, Zheng; Miao, Zhiming; Dai, Chao; Wang, Yang; Liu, Yi; Gong, Qihuang; Wu, Chengyin

doi:10.1021/acs.jpclett.0c02337

“…Indeed, the recollision between the electron and its parent ion greatly increases the electron kinetic energy and electron yields in the plateau region. This may lead to an increase of the intensity of the 337 nm emission, especially in the case of a linearly polarized laser field [49]. On the other hand, in the case of the circularly polarized laser, the probability of recollision between the electron and its parent ion is low, and the high energy electrons due to rescattering may be neglected.…”

Section: Resultsmentioning

confidence: 99%

Laser Driven Fluorescence Emission in a Nitrogen Gas Jet at 100 MHz Repetition Rate

Zhang,

Hua,

Yu

et al. 2021

Preprint

0

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We report the fluorescence emission which is driven by femtosecond laser pulses with a repetition rate of 100 MHz and a center wavelength of 1040 nm in a nitrogen gas jet. The experiment is performed in a femtosecond enhancement cavity coupled with high repetition rate laser for the first time to the best of our knowledge. In contrast to previous observation at low repetition rate with a nitrogen gas jet, where the 391 nm radiation was observed but the 337 nm emission was missing, the 337 nm emission is 3 times stronger than the 391 nm emission in our experiment. By examining the dependence of the radiation intensity on the flow rate of the nitrogen gas and the polarization of the pump pulse, the formation mechanism of the N2(C 3 Πu) triplet excited state, i.e., the upper state of the 337 nm emission, is investigated. We attribute the main excitation process to the inelastic collision excitation process, and exclude the possibility of the dissociative recombination as the dominate pathway. The role of the steady state plasma that is generated under our experimental conditions is also discussed.

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“…The mechanism responsible for populating the state is still debated. Arnold et al 37 found in their study that ISC from an intermediate excited singlet state is the dominant formation path, whereas Zheng et al 38 in a recent paper, conclude that is populated through impact excitation of ( ) by energetic electrons.…”

Section: Methodsmentioning

confidence: 98%

Laser-induced thermal grating spectroscopy based on femtosecond laser multi-photon absorption

Ruchkina

¹

,

Hot

²

,

Ding

³

et al. 2021

Sci Rep

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Laser-induced grating spectroscopy (LIGS) is for the first time explored in a configuration based on the crossing of two focused femtosecond (fs) laser pulses (800-nm wavelength) and a focused continuous-wave (cw) laser beam (532-nm wavelength). A thermal grating was formed by multi-photon absorption of the fs-laser pulses by $$\hbox {N}_{{2}}$$ N 2 with a pulse energy around 700 $$\upmu $$ μ J ($$\sim $$ ∼ 45 TW/$$\hbox {cm}^{2}$$ cm 2 ). The feasibility of this LIGS configuration was investigated for thermometry in heated nitrogen gas flows. The temperature was varied from room temperature up to 750 K, producing strong single-shot LIGS signals. A model based on the solution of the linearized hydrodynamic equations was used to extract temperature information from single-shot experimental data, and the results show excellent agreement with the thermocouple measurements. Furthermore, the fluorescence produced by the fs-laser pulses was investigated. This study indicates an 8-photon absorption pathway for $$\hbox {N}_{{2}}$$ N 2 in order to reach the $$\hbox {B}^{3}\Pi _{g}$$ B 3 Π g state from the ground state, and 8 + 5 photon excitation to reach the $$\hbox {B}^{2}\Sigma _{u}^{+}$$ B 2 Σ u + state of the $$\hbox {N}_{2}^{+}$$ N 2 + ion. At pulse energies higher than 1 mJ, the LIGS signal was disturbed due to the generation of plasma. Additionally, measurements in argon gas and air were performed, where the LIGS signal for argon shows lower intensity compared to air and $$\hbox {N}_{{2}}$$ N 2 .

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“…The fluorescence emissions at 337 nm and 391 nm can be generally observed and controlled in these scenarios, and from which alternative schemes have been derived for explaining the formation of the N 2 (C 3 Π u ) and N + 2 (B 2 Σ + u ). The former is attributed to three main possible schemes: collision-excitation [5,13,14,[21][22][23], collision-assisted intersystem crossing [13,24,25] and dissociative recombination through the reactions of N [2,[26][27][28], while the latter is attributed to two main possible schemes: one is multi-photon ionization of the inner-valence electrons of N 2 [29]; the other is collision ionization of N 2 with a high energy electron [5,13,30]. Additionally, the second harmonic emission as well as supercontinuum emission can serve as a self-seeding pulse to start and enhance the lasing in N + 2 molecules [17,31].…”

Section: Introductionmentioning

confidence: 99%

Nitrogen fluorescence emission pumped by femtosecond optical vortex beams

Chen

¹

,

Man²,

Liu³

et al. 2023

Front. Phys.

3

0

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An experimental investigation on nitrogen fluorescence emissions pumped by a single 800 nm fs optical vortex (OV) beam with different topological charges (TC) is reported. The intensity of the two prototype emission lines from neutral nitrogen molecules (N2) and molecular nitrogen ions (N2+), i.e., 337 nm and 391 nm, respectively, shows different TC dependences: the former slightly decreases as the TC increases, while the latter sharply decreases as the TC changes from zero to a non-zero value. The dependences of the 337-nm and 391-nm emission intensity on pulse energy are also different: the former shows a linear variation for different TCs, while the latter has an abrupt change in the slope when changing the TC. Furthermore, the dependence of the 337-nm emission intensity on gas pressure exhibits a plateau which is universal for different TCs. In contrast, the dependence of the 391-nm emission intensity on gas pressure shows an apparent hump which is respective of the TC. These actual new results will facilitate further theoretical study on the formation dynamics of the nitrogen fluorescence emissions induced by the OV beam, and inspire that such beam can been taken as a unique pure optical tool to manipulate the transitions between different electronic-vibrational states.

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Formation Mechanism of Excited Neutral Nitrogen Molecules Pumped by Intense Femtosecond Laser Pulses

Cited by 8 publications

References 33 publications

Laser Driven Fluorescence Emission in a Nitrogen Gas Jet at 100 MHz Repetition Rate

Laser Driven Fluorescence Emission in a Nitrogen Gas Jet at 100 MHz Repetition Rate

Laser-induced thermal grating spectroscopy based on femtosecond laser multi-photon absorption

Nitrogen fluorescence emission pumped by femtosecond optical vortex beams

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