Spatial distribution of nitrogen fluorescence emission induced by femtosecond laser filamentation in air

doi:10.7498/aps.70.20201704

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	Spatial distribution of nitrogen fluorescence emission induced by femtosecond laser filamentation in air
	Y. Zhang; S. Lin; Y.-F. Zhang; H. Zhang; M.-Y. Chang; M. Yu; Y.-Q. Wang; X.-M. Cai; Y.-F. Jiang; A.-M. Chen
刊名	Wuli Xuebao/Acta Physica Sinica
	2021
卷号	70 期号:13
ISSN号	10003290
DOI	10.7498/aps.70.20201704
英文摘要	As a major component in the air, nitrogen emits fluorescence when it interacts with intensive laser field. The fluorescence comes from the first negative band system (B2u+X2g+ transition) of and the second positive band system (C3IIu+B3IIg+ transition) of N2 Under the action of high-intensity femtosecond laser, N2 can be directly photo-ionized into N2(B2u+), which results in fluorescence emission of N2+. In the process of femtosecond laser filament formation, the dynamic processes such as ionization and excitation of nitrogen molecules are affected by the laser intensity distribution and laser polarization direction. The products show different distributions in the propagation direction and radial space, which, in turn, affects its light emission. Therefore, it is necessary to further ascertain its generation mechanism through the spatial distribution of nitrogen fluorescence. In this experiment, the spatial distribution of the nitrogen fluorescence emission generated by linearly polarized femtosecond laser pulse filaments in air is measured. By changing the polarization direction of the laser to study the distribution of nitrogen fluorescence in the radial plane, it is found that the fluorescence emission of N2+ is more intense in the direction perpendicular to the laser polarization, while it is weaker in the direction parallel to the laser polarization. The nitrogen fluorescence emission has the same intensity in all directions. The ionization probability of a linear molecule depends on the angle between the laser polarization direction and the molecular axis, which is maximum (minimum) when the angle is 0(90). The N2 gas is more likely to be ionized in the laser polarization direction, the nitrogen molecular ions N2+ and electrons are separated in the direction parallel to the laser polarization. Therefore, more ions (N2+) are generated in the direction parallel to the laser polarization, and the fluorescence emission of N2+ is more intense. Along the propagation direction of the laser, it is found that the fluorescence of N2 appears before the fluorescence of N2+ and disappears after the fluorescence of N2+ has vanished. This is due to the fact that N2 can be ionized into N2+(B2u+) at the position of high enough laser intensity, thus emitting fluorescence of N2+. However, the laser energy is not enough to ionize nitrogen at the beginning and end of laser transmission, but it can generate N2, which emits nitrogen fluorescence through the process of intersystem crossing N2ISC N2(C3IIu+). The spatial distribution of nitrogen fluorescence emission during femtosecond laser filament formation shows that in the case of short focal length, the intersystem crossing scheme can explain the formation of N2(C3IIu+). This research is helpful in understanding the mechanism of nitrogen fluorescence emission. 2021 Chinese Physical Society.
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内容类型	期刊论文
源URL	[http://ir.ciomp.ac.cn/handle/181722/65644]
专题	中国科学院长春光学精密机械与物理研究所
推荐引用方式 GB/T 7714	Y. Zhang,S. Lin,Y.-F. Zhang,et al. Spatial distribution of nitrogen fluorescence emission induced by femtosecond laser filamentation in air[J]. Wuli Xuebao/Acta Physica Sinica,2021,70(13).
APA	Y. Zhang.,S. Lin.,Y.-F. Zhang.,H. Zhang.,M.-Y. Chang.,...&S.-Y. Li and M.-X. Jin.(2021).Spatial distribution of nitrogen fluorescence emission induced by femtosecond laser filamentation in air.Wuli Xuebao/Acta Physica Sinica,70(13).
MLA	Y. Zhang,et al."Spatial distribution of nitrogen fluorescence emission induced by femtosecond laser filamentation in air".Wuli Xuebao/Acta Physica Sinica 70.13(2021).