Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Single-color two-photon spectroscopy of Rydberg states in electric
  fields   Rydberg states of atomic helium with principal quantum numbers ranging from
n=20 to n=100 have been prepared by non-resonance-enhanced single-color
two-photon excitation from the metastable 2 {^3}S{_1} state. Photoexcitation
was carried out using linearly and circularly polarized pulsed laser radiation.
In the case of excitation with circularly polarized radiation, Rydberg states
with azimuthal quantum number |m_{\ell}|=2 were prepared in zero electric
field, and in homogeneous electric fields oriented parallel to the propagation
axis of the laser radiation. In sufficiently strong electric fields, individual
Rydberg-Stark states were resolved spectroscopically, highlighting the
suitability of non-resonance-enhanced multiphoton excitation schemes for the
preparation of long-lived high-|m_{\ell}| hydrogenic Rydberg states for
deceleration and trapping experiments. Applications of similar schemes for
Doppler-free excitation of positronium atoms to Rydberg states are also
discussed.

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The categories of this paper are: quant-ph
35
The categories of this paper are: mtrl-th
25
The categories of this paper are: patt-sol
16
The categories of this paper are: stat
37
The categories of this paper are: supr-con
26
The categories of this paper are: bayes-an
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The categories of this paper are: chem-ph
21
The categories of this paper are: adap-org
4
The categories of this paper are: cond-mat
33
The categories of this paper are: plasm-ph
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The categories of this paper are: alg-geom
5
The categories of this paper are: gr-qc
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The categories of this paper are: acc-phys
27
The categories of this paper are: comp-gas
30
The categories of this paper are: q-alg
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The categories of this paper are: dg-ga