Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The use of relativistic action in strong-field nonlinear photoionization   Nonlinear relativistic ionization phenomena induced by a strong linearly
polarized laser field are considered. The starting point is the classical
relativistic action for a free electron moving in the electromagnetic field
created by a strong laser beam. This action has been used to calculate
semiclassical transition rates. Simple analytical expressions for the
ionization rate, the photoelectron emission velocity and for the drift momentum
distribution of the photoelectron have been found. The analytical formulas
apply to nonrelativistic bound systems as well as to initial states with an
energy corresponding to the upper boundary of the lower continuum and to the
tunnel as well as the multiphoton regime. In the case of a nonrelativistic
bound system we recover the Keldysh formula for the ionization rate.
Relativistic effects in the initial state lead to a weak enhancement of the
rate of sub-barrier ionization and to the appearance of a nonzero photoelectron
leaving velocity.

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The categories of this paper are: econ
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The categories of this paper are: dg-ga
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The categories of this paper are: funct-an
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The categories of this paper are: eess
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The categories of this paper are: q-bio
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The categories of this paper are: math-ph
0
The categories of this paper are: hep-ph
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The categories of this paper are: supr-con
35
The categories of this paper are: mtrl-th
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The categories of this paper are: quant-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: hep-th
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The categories of this paper are: q-alg
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The categories of this paper are: adap-org
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The categories of this paper are: acc-phys
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The categories of this paper are: bayes-an