Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Bright single-cycle terahertz source based on gas cells irradiated by
  two-color laser pulses   We study the excitation of electron currents in a transparent cell of
sub-millimeter size filled by an atomic gas and illuminated by an intense
two-color femtosecond laser pulse. The pulse consists of a strong fundamental
component and its second harmonic of low intensity, both circularly polarized.
We show that for sufficiently small $20\mu$m cells the plasma oscillation
excited by asymmetric ionization is almost spatially homogeneous within the
interaction volume. This coherent dipole plasma oscillation results in a
remarkably efficient conversion of the electron energy into that of radiation
emitted in the terahertz frequency domain. Simultaneously, strong quasi-static
electric fields of maximal strength $E_m\simeq 10$MV/cm are shown to exist
inside the cell during several hundred femtoseconds after the ionizing
two-color laser pulse has gone.

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The categories of this paper are: gr-qc
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The categories of this paper are: nucl-th
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The categories of this paper are: bayes-an
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The categories of this paper are: astro-ph
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The categories of this paper are: alg-geom
35
The categories of this paper are: mtrl-th
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The categories of this paper are: plasm-ph
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The categories of this paper are: q-fin
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The categories of this paper are: q-alg
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The categories of this paper are: solv-int
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The categories of this paper are: eess
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The categories of this paper are: cond-mat
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The categories of this paper are: patt-sol
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The categories of this paper are: cmp-lg
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The categories of this paper are: supr-con
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The categories of this paper are: dg-ga