Population dynamics of molecular nitrogen initiated by intense femtosecond laser pulses
PHYSICAL REVIEW A(2015)
摘要
Tunneling ionization is one of the fundamental processes for molecules in intense laser fields, and the tunnelionized molecules are in various electronic states. Here, we report an experimental study of the population dynamics of N-2+(B-2 Sigma(+)(u)) and N-2+(X-2 Sigma(+)(g)) generated in intense femtosecond laser fields by simultaneously measuring the fluorescence emission spectra and the transmission spectra. The results reveal that the population inversion exists between N-2+(B-2 Sigma(+)(u)) and N-2+(X-2 Sigma(+)(g)). But the population difference is much smaller than the absolute population of N-2+(B-2 Sigma(+)(u)) . The present study provides insight into understanding the observation of the generation of an air laser from the tunnel-ionized nitrogen molecules, which has been attributed to the population inversion between N-2+(B-2 Sigma(+)(u)) and N-2+(X-2 Sigma(+)(g)) in intense femtosecond laser fields at 800-nm wavelengths.
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