Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Two symmetric four-wave mixing signals generated in a medium with
  anomalous refractive index   We report experimental and theoretical results of two symmetrical signals of
degenerate four-wave mixing generated in rubidium vapor. Both nonlinear signals
are induced by two almost copropagating laser beams, with $\vec{k}_{a}$ and
$\vec{k}_{b}$ wave-vectors, and detected simultaneously in the
$2\vec{k}_{a}-\vec{k}_{b}$ and $2\vec{k}_{b}-\vec{k}_{a}$ directions. In each
direction, we observe a single peak when the two beams are tuned on the closed
transition $^{85}$Rb$~5S_{1/2} (F=3) \rightarrow 5P_{3/2} (F=4)$. The
excitation spectra reveal a small frequency separation between the two peaks,
which is explained when propagation effects are taken into account.
Furthermore, our theoretical analysis shows that a correct description of the
frequency position of each peak is obtained only if coherent effects such as
electromagnetically induced absorption are included.

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The categories of this paper are: astro-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: nlin
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The categories of this paper are: eess
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The categories of this paper are: alg-geom
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The categories of this paper are: q-fin
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The categories of this paper are: hep-ph
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The categories of this paper are: solv-int
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The categories of this paper are: gr-qc
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The categories of this paper are: funct-an
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The categories of this paper are: nucl-th
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The categories of this paper are: math
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The categories of this paper are: cs
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The categories of this paper are: patt-sol
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The categories of this paper are: nucl-ex
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The categories of this paper are: chem-ph