Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Amplification of surface plasmon polaritons in the presence of
  nonlinearity and spectral signatures of threshold crossover   We describe effects of nonlinearity on propagation of surface plasmon
polaritons (SPPs) at an interface between a metal and an amplifying medium of
the externally pumped two-level atoms. Using Maxwell equations we derive the
nonlinear dispersion law and demonstrate that, the nonlinear saturation of the
linear gain leads to formation of stationary SPP modes with the intensities
independent from the propagation distance. Transition to the regime of
stationary propagation is similar to the threshold crossover in lasers and
leads to narrowing of the SPP spectrum.

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The categories of this paper are: eess
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The categories of this paper are: q-alg
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The categories of this paper are: adap-org
35
The categories of this paper are: mtrl-th
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The categories of this paper are: nucl-th
5
The categories of this paper are: gr-qc
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The categories of this paper are: q-fin
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The categories of this paper are: funct-an
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The categories of this paper are: math-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: hep-lat
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The categories of this paper are: bayes-an
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The categories of this paper are: astro-ph
33
The categories of this paper are: plasm-ph
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The categories of this paper are: atom-ph
25
The categories of this paper are: patt-sol