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Related Concept Videos

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The spin state of an NMR-active nucleus can have a slight effect on its immediate electronic environment. This effect propagates through the intervening bonds and affects the electronic environments of NMR-active nuclei up to three bonds away; occasionally, even farther. This phenomenon is called spin–spin coupling or J-coupling. Coupling interactions are mutual and result in small changes in the absorption frequencies of both nuclei involved. While nuclei of the same element are involved...
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Sub-10-fs population inversion in N2(+) in air lasing through multiple state coupling.

Huailiang Xu1,2, Erik Lötstedt1, Atsushi Iwasaki1

  • 1Department of Chemistry, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.

Nature Communications
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Intense laser pulses in air create lasing by exciting nitrogen molecules (N2(+)). This study reveals population inversion occurs instantaneously via post-ionization coupling, clarifying atmospheric lasing mechanisms.

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Area of Science:

  • Physics
  • Physical Chemistry
  • Optics

Background:

  • Laser filamentation in air has potential applications in remote sensing.
  • Recent findings show filamentation can induce lasing in excited nitrogen ions (N2(+)).
  • This contrasts with the expectation that molecular ions are formed in ground electronic states.

Purpose of the Study:

  • To elucidate the mechanism behind population inversion in laser-induced atmospheric lasing.
  • To investigate the temporal dynamics of N2(+) excitation during filamentation.

Main Methods:

  • Experimental investigation using few-cycle laser pulses.
  • Numerical simulations to model electronic state couplings in N2(+).

Main Results:

  • Lasing at 391 nm was observed to occur instantaneously after N2(+) generation.
  • Numerical simulations confirmed population inversion is driven by post-ionization couplings between the lowest three electronic states of N2(+).

Conclusions:

  • Post-ionization coupling is the mechanism responsible for population inversion in atmospheric lasing.
  • This coupling mechanism is likely general for atmospheric lasing phenomena.
  • The findings resolve controversy regarding the origin of air lasing.