Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Ultracold Neutral Plasmas   Ultracold neutral plasmas are formed by photoionizing laser-cooled atoms near
the ionization threshold. Through the application of atomic physics techniques
and diagnostics, these experiments stretch the boundaries of traditional
neutral plasma physics. The electron temperature in these plasmas ranges from
1-1000 K and the ion temperature is around 1 K. The density can approach
$10^{11}$ cm$^{-3}$. Fundamental interest stems from the possibility of
creating strongly-coupled plasmas, but recombination, collective modes, and
thermalization in these systems have also been studied. Optical absorption
images of a strontium plasma, using the Sr$^+$ ${^2S\_{1/2}} -> {^2P\_{1/2}}$
transition at 422 nm, depict the density profile of the plasma, and probe
kinetics on a 50 ns time-scale. The Doppler-broadened ion absorption spectrum
measures the ion velocity distribution, which gives an accurate measure of the
ion dynamics in the first microsecond after photoionization.

17
The categories of this paper are: q-fin
4
The categories of this paper are: cond-mat
33
The categories of this paper are: plasm-ph
11
The categories of this paper are: hep-lat
12
The categories of this paper are: nucl-th
20
The categories of this paper are: acc-phys
37
The categories of this paper are: supr-con
35
The categories of this paper are: mtrl-th
19
The categories of this paper are: eess
1
The categories of this paper are: cs
30
The categories of this paper are: q-alg
32
The categories of this paper are: atom-ph
18
The categories of this paper are: econ
7
The categories of this paper are: hep-th
0
The categories of this paper are: hep-ph
22
The categories of this paper are: chao-dyn