Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Rotational Quantum Beat Lasing Without Inversion   In standard lasers, light amplification requires population inversion between
an upper and a lower state to break the reciprocity between absorption and
stimulated emission. However, in a medium prepared in a specific superposition
state, quantum interference may fully suppress absorption while leaving
stimulated emission intact, opening the possibility of lasing without
inversion. Here we show that lasing without inversion arises naturally during
propagation of intense femtosecond laser pulses in air. It is triggered by the
combination of molecular ionization and molecular alignment, both unavoidable
in intense light fields. The effect could enable inversionless amplification of
broadband radiation in many molecular gases, opening unusual opportunities for
remote sensing.

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The categories of this paper are: comp-gas
10
The categories of this paper are: q-bio
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The categories of this paper are: q-alg
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The categories of this paper are: hep-lat
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The categories of this paper are: hep-ex
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The categories of this paper are: hep-th
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The categories of this paper are: gr-qc
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The categories of this paper are: nucl-ex
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The categories of this paper are: ao-sci
9
The categories of this paper are: nlin
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The categories of this paper are: funct-an
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The categories of this paper are: patt-sol
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The categories of this paper are: acc-phys
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The categories of this paper are: math-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: math