Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Direct femtosecond pulse compression with miniature-sized Bragg
  cholesteric liquid crystal   Direct compression of femtosecond optical pulses from a Ti:sapphire laser
oscillator was realized with a cholesteric liquid crystal acting as a nonlinear
1D periodic Bragg grating. With a 6-um thick sample, the pulse duration could
be compressed from 100 to 48 femtoseconds. Coupled-mode equations for forward
and backward waves were employed to simulate the dynamics therein and good
agreement between theory and experiment was obtained.

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The categories of this paper are: q-alg
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The categories of this paper are: atom-ph
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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: nlin
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The categories of this paper are: stat
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The categories of this paper are: comp-gas
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The categories of this paper are: plasm-ph
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The categories of this paper are: bayes-an
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The categories of this paper are: hep-ph
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The categories of this paper are: adap-org
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The categories of this paper are: hep-th
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The categories of this paper are: math-ph
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The categories of this paper are: q-fin
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The categories of this paper are: supr-con
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The categories of this paper are: funct-an