Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Population Redistribution among Multiple Electronic States of Molecular
  Nitrogen Ions in Strong Laser Fields   We carry out a combined theoretical and experimental investigation on the
population distributions in the ground and excited states of tunnel ionized N2
molecules at various driver wavelengths in the near- and mid-infrared range.
Our results reveal that efficient couplings (i.e., population exchanges)
between the ground state and the excited states occur in strong laser fields.
The couplings result in the population inversion between the ground and the
excited states at the wavelengths near 800 nm, which is verified by our
experiment by observing the amplification of a seed at ~391 nm. The result
provides insight into the mechanism of free-space nitrogen ion lasers generated
in remote air with strong femtosecond laser pulses.

28
The categories of this paper are: alg-geom
9
The categories of this paper are: nlin
16
The categories of this paper are: stat
30
The categories of this paper are: q-alg
1
The categories of this paper are: cs
10
The categories of this paper are: q-bio
22
The categories of this paper are: chao-dyn
25
The categories of this paper are: patt-sol
11
The categories of this paper are: hep-lat
27
The categories of this paper are: comp-gas
8
The categories of this paper are: hep-ex
29
The categories of this paper are: funct-an
12
The categories of this paper are: nucl-th
23
The categories of this paper are: solv-int
6
The categories of this paper are: astro-ph
15
The categories of this paper are: nucl-ex