Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Soft X-ray harmonic comb from relativistic electron spikes   We demonstrate a new high-order harmonic generation mechanism reaching the
`water window' spectral region in experiments with multi-terawatt femtosecond
lasers irradiating gas jets. A few hundred harmonic orders are resolved, giving
uJ/sr pulses. Harmonics are collectively emitted by an oscillating electron
spike formed at the joint of the boundaries of a cavity and bow wave created by
a relativistically self-focusing laser in underdense plasma. The spike
sharpness and stability are explained by catastrophe theory. The mechanism is
corroborated by particle-in-cell simulations.

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The categories of this paper are: bayes-an
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The categories of this paper are: atom-ph
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The categories of this paper are: dg-ga
4
The categories of this paper are: cond-mat
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The categories of this paper are: acc-phys
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The categories of this paper are: chem-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: hep-th
1
The categories of this paper are: cs
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The categories of this paper are: alg-geom
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The categories of this paper are: q-alg
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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: ao-sci
15
The categories of this paper are: nucl-ex
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The categories of this paper are: chao-dyn