Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Modulation instability of structured-light beams in negative-index
  metamaterials   One of the most fundamental properties of isotropic negative-index
metamaterials, namely opposite directionality of the Poynting vector and the
wavevector, enable many novel linear and nonlinear regimes of light-matter
interactions. Here, we predict distinct characteristics of azimuthal modulation
instability of optical vortices with different topological charges in
negative-index metamaterials with Kerr-type and saturable nonlinearity. We
derive an analytical expression for the spatial modulation-instability gain for
the Kerr-nonlinearity case and show that a specific condition relating the
diffraction and the nonlinear lengths must be fulfilled for the azimuthal
modulation instability to occur. Finally, we investigate the rotation of the
necklace beams due to the transfer of orbital angular momentum of the
generating vortex on the movement of solitary necklace beams. We show that the
direction of rotation is opposite in positive- and negative-index materials.

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The categories of this paper are: astro-ph
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The categories of this paper are: nucl-ex
27
The categories of this paper are: comp-gas
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The categories of this paper are: funct-an
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The categories of this paper are: hep-lat
34
The categories of this paper are: chem-ph
0
The categories of this paper are: hep-ph
26
The categories of this paper are: bayes-an
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The categories of this paper are: chao-dyn
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The categories of this paper are: q-bio
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The categories of this paper are: adap-org
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The categories of this paper are: patt-sol
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The categories of this paper are: mtrl-th
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The categories of this paper are: hep-ex
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The categories of this paper are: math-ph
28
The categories of this paper are: alg-geom