Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Understanding tunneling ionization of atoms in laser fields with the
  essence of multiphoton absorption   The elaborate energy and momentum spectra of ionized electrons from atoms in
laser fields suggest that the ionization dynamics described by tunneling theory
should be modified. Although many efforts have been done within semiclassical
models, there are few discussions describing multiphoton absorption process
with quantum framework. In this letter, by comparing the results obtained with
the time-dependent Schrodinger equation (TDSE) and Keldysh-Faisal-Reiss (KFR)
theory, we have studied the nonperturbative effects of ionization dynamics
beyond KFR theory. The difference in momentum spectra between multiphoton and
tunneling regimes is understood in a unified picture with virtual multiphoton
absorption processes. For the multiphoton regime, the momentum spectra can be
obtained by coherent interference of each periodic contribution. However, the
interference of multiphoton absorption peaks will result in the complex
structure of virtual multiphoton bands in the tunneling regime. It is shown
that the virtual spectra will be almost continuous in the tunneling regime
instead of the discrete levels in the multiphoton regime. Finally, with a model
combining TDSE and KFR theory, we have tried to understand the different
effects of virtual multiphoton processes on ionization dynamics.

6
The categories of this paper are: astro-ph
19
The categories of this paper are: eess
32
The categories of this paper are: atom-ph
18
The categories of this paper are: econ
14
The categories of this paper are: math-ph
2
The categories of this paper are: math
17
The categories of this paper are: q-fin
35
The categories of this paper are: mtrl-th
31
The categories of this paper are: ao-sci
22
The categories of this paper are: chao-dyn
11
The categories of this paper are: hep-lat
4
The categories of this paper are: cond-mat
36
The categories of this paper are: cmp-lg
30
The categories of this paper are: q-alg
27
The categories of this paper are: comp-gas
21
The categories of this paper are: adap-org