Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Cluster emission under femtosecond laser ablation of silicon   Rich populations of clusters have been observed after femtosecond laser
ablation of bulk silicon in vacuum. Size and velocity distributions of the
clusters as well as their charge states have been analyzed by reflectron
time-of-flight mass spectrometry. An efficient emission of both neutral silicon
clusters Sin (up to n = 6) and their cations Sin+ (up to n = 10) has been
observed. The clusters are formed even at very low laser fluences, below
ablation threshold, and their relative yield increases with fluence. We show
the dependencies of the cluster yield as well as the expansion dynamics on both
laser wavelength and laser fluence. The mechanisms of the cluster formation are
discussed.

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The categories of this paper are: alg-geom
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The categories of this paper are: adap-org
35
The categories of this paper are: mtrl-th
33
The categories of this paper are: plasm-ph
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The categories of this paper are: patt-sol
22
The categories of this paper are: chao-dyn
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The categories of this paper are: dg-ga
20
The categories of this paper are: acc-phys
9
The categories of this paper are: nlin
34
The categories of this paper are: chem-ph
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The categories of this paper are: q-alg
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The categories of this paper are: bayes-an
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The categories of this paper are: q-fin
2
The categories of this paper are: math
6
The categories of this paper are: astro-ph
13
The categories of this paper are: quant-ph