Formation Dynamics of Excited Neutral Nitrogen Molecules inside Femtosecond Laser Filaments

Danylo, Rostyslav; Zhang, Xiang; Fan, Zhiyuan; Zhou, Dongjie; Lu, Qi; Zhou, Bin; Liang, Qi; Zhuang, Songlin; Houard, Aurélien; Mysyrowicz, A.; Oliva, Eduardo; Liu, Yi

doi:10.1103/physrevlett.123.243203

Cited by 21 publications

(26 citation statements)

References 30 publications

(39 reference statements)

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“…5 shows that the emission at 337 nm is stronger with linearly polarized laser than with circularly polarized laser. This observation is in agreement with two previous reports in the low intensity regime [9,46], where a stronger 337 nm emission is also observed with linearly polarized laser. On the other hand, these results are different from those experiments which are operated with high laser intensity, where circularly polarized laser generates stronger 337 nm emission [6][7][8][9].The key difference induced by the polarization of the laser is that, with linearly polarized laser pulses, most free electrons are left with low kinetic energy at the end of the pump pulse because they are alternately accelerated and decelerated by the laser field during every optical cycle.…”

Section: Resultssupporting

confidence: 94%

“…This mechanism explains the result in the high intensity regime very well, but leaves the result in the low intensity regime as a puzzle since electrons that are generated with linear polarized laser don't have enough energy to excite N 2 to the C 3 Π u state. Recently, Liu et al proposed the multiple collision as a possible candidate mechanism [46]. However, it is worthy to note that electrons generated due to recollisions have not been taken into account in the above discussions [6][7][8][9]46].…”

Section: Resultsmentioning

confidence: 99%

“…Recently, Liu et al proposed the multiple collision as a possible candidate mechanism [46]. However, it is worthy to note that electrons generated due to recollisions have not been taken into account in the above discussions [6][7][8][9]46]. Indeed, the recollision between the electron and its parent ion greatly increases the electron kinetic energy and electron yields in the plateau region.…”

Section: Resultsmentioning

confidence: 99%

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

Zhang,

Hua,

et al. 2021

Preprint

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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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Section: Resultssupporting

confidence: 94%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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

Zhang,

Hua,

et al. 2021

Preprint

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“…Zhao et al 35 found that the native CN band-head persisted before 700–800 ns delay time (the delay time chosen in our experiment is 400 ns). As for the nitrogen band, the N 2 + fragments could come from 36 : collision of resultant fragments (NH radicals) within the dense plasma or with ambient particles or with energetic electrons. Since N–N bond structure might not exist in coals, N 2 + fragments are probably formed due to ionization of air by energetic electrons at the interaction zone on coal surface—which is the claim behind enhanced residual thermal energy deposition explained later in this paper.…”

Section: Resultsmentioning

confidence: 99%

Evaluation of femtosecond laser-induced breakdown spectroscopy system as an offline coal analyzer

Sheta

Hou

Wang

et al. 2021

Sci Rep

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Developments in femtosecond laser induced breakdown spectroscopy (fs-LIBS) applications during the last two decades have further centered on innovative métier tie-in to the advantageous properties of femtosecond laser ablation (fs-LA) introduced into LIBS. Yet, for industrially-oriented application like coal analysis, no research has exposed to view the analytical capabilities of fs-LA in enhancing the physical processes of coal ablation and the impact into quantitative correlation of spectra and data modeling. In a huge coal market, fast and accurate analysis of coal property is eminently important for coal pricing, combustion optimization, and pollution reduction. Moreover, there is a thirst need of precision standardization for coal analyzers in use. In this letter, the analytical performance of a one-box femtosecond laser system is evaluated relative to an industrially applied coal analyzer based on five objectives/measures: spectral correlation, relative sensitivity factors, craters topology, plasma parameters, and repeatability. Despite high-threshold operation parameters of the fs system, competitive results are achieved compared to the optimized analytical conditions of the ns-coal analyzer. Studies targeting the in-field optimization of fs-LIBS systems for coal analysis can potentially provide insights into fs-plasma hydrodynamics under harsh conditions, instrumental customization, and pave the way for a competitive next-generation of coal analyzers.

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“…In contrast, the direct imaging of air plasma is based on the fluorescence emission of the excited neutral molecules in the 𝐶 3 Π + 𝑢 state and ionic nitrogen molecules in the 𝐵 2 Σ + 𝑢 state [29]. The excited neutral nitrogen molecules N 2 𝐶 3 Π + 𝑢 are mainly formed via collision excitation of the nitrogen molecules in the ground state by energetic electron with kinetic energy above the threshold energy of 14 eV [31,32]. For the excited ionic nitrogen molecules 𝑁 + 2 𝐵 2 Σ + 𝑢 , they origin from the ionization of the inner electron in the HOMO-2 orbit of 𝑁 2 [29], which obviously requires much higher laser intensity with respect to that of HOMO orbit.…”

Section: Numerical Simulation For the Air Plasma Formation And Furthe...mentioning

confidence: 99%

Optical vortex coronagraph imaging of a laser-induced plasma filament

Liang,

Huang,

Mou

et al. 2021

Preprint

Self Cite

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A high contrast imaging technique based on an optical vortex coronagraph (OVC) is used to measure the spatial phase profile induced by an air plasma generated by a femtosecond laser pulse. The sensitivity of the OVC method significantly surpassed both in-line holographic and direct imaging methods based on air plasma fluorescence. The estimated phase sensitivity of 0.046 waves provides opportunities for OVC applications in areas such as bioimaging, material characterization, as well as plasma diagnostics.

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Formation Dynamics of Excited Neutral Nitrogen Molecules inside Femtosecond Laser Filaments

Cited by 21 publications

References 30 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

Evaluation of femtosecond laser-induced breakdown spectroscopy system as an offline coal analyzer

Optical vortex coronagraph imaging of a laser-induced plasma filament

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