Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: An upper limit to the orbital angular momentum of a vortex-carrying
  ultrashort pulse   The magnitude of the topological charge of the vortex of a ring-shaped pulse
is found to be limited by the squared mean frequency of the pulse spectrum at
the ring relative to its variance. This limitation implies a upper bound to the
orbital angular momentum carried by a pulse, and a lower bound to the duration
for a pulse to carry any orbital angular momentum.

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The categories of this paper are: econ
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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: hep-ex
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The categories of this paper are: hep-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: chao-dyn
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The categories of this paper are: acc-phys
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The categories of this paper are: mtrl-th
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The categories of this paper are: chem-ph
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The categories of this paper are: solv-int
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The categories of this paper are: astro-ph
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The categories of this paper are: funct-an
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The categories of this paper are: nucl-ex
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The categories of this paper are: math
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The categories of this paper are: q-alg