Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: ALFA: First Operational Experience of the MPE/MPIA Laser Guide Star
  System for Adaptive Optics   The sodium laser guide star adaptive optics system ALFA has been constructed
at the Calar Alto 3.5-m telescope. Following the first detection of the laser
beacon on the wavefront sensor in 1997 the system is now being optimized for
best performance. In this contribution we discuss the current status of the
launch beam and the planned improvements and upgrades. We report on the
performance level achieved when it is used with the adaptive optics system, and
relate various aspects of our experience during operation of the system. We
have begun to produce scientific results and mention two of these.

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The categories of this paper are: cs
31
The categories of this paper are: ao-sci
4
The categories of this paper are: cond-mat
12
The categories of this paper are: nucl-th
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The categories of this paper are: math-ph
9
The categories of this paper are: nlin
18
The categories of this paper are: econ
25
The categories of this paper are: patt-sol
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The categories of this paper are: hep-th
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The categories of this paper are: q-fin
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The categories of this paper are: dg-ga
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The categories of this paper are: q-bio
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The categories of this paper are: math
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The categories of this paper are: chem-ph
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The categories of this paper are: mtrl-th
16
The categories of this paper are: stat