Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Field-free molecular alignment probed by the free electron laser in
  Hamburg (FLASH)   We report experiments on field-free molecular alignment performed at FLASH,
the free electron laser (FEL) in Hamburg. The impulsive alignment induced by a
100 fs near-infrared laser pulse in a rotationally cold CO_2 sample is
characterized by ionizing and dissociating the molecules with a time delayed
extreme ultra-violet (XUV) FEL pulse. The time-dependent angular distributions
of ionic fragments measured by a velocity map imaging spectrometer shows rapid
changes associated with the induced rotational dynamics. The experimental
results also show hints of a dissociation process that depends non-linearly on
the XUV intensity. With samples of aligned molecules at FLASH, experiments
using ultrashort XUV pulses become possible in the molecular frame, which will
enable new insights into the understanding of molecules and their interactions.

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The categories of this paper are: cs
21
The categories of this paper are: adap-org
23
The categories of this paper are: solv-int
9
The categories of this paper are: nlin
4
The categories of this paper are: cond-mat
36
The categories of this paper are: cmp-lg
32
The categories of this paper are: atom-ph
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The categories of this paper are: quant-ph
35
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: eess
37
The categories of this paper are: supr-con
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The categories of this paper are: hep-th
16
The categories of this paper are: stat
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The categories of this paper are: q-fin
28
The categories of this paper are: alg-geom