Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Hybrid optical pumping of optically dense alkali-metal vapor without
  quenching gas   Optical pumping of an optically thick atomic vapor typically requires a
quenching buffer gas, such as N$_{2}$, to prevent radiation trapping of
unpolarized photons which would depolarize the atoms. We show that optical
pumping of a trace contamination of Rb present in K metal results in a 4.5
times higher polarization of K than direct optical pumping of K in the absence
of N$_{2}$. Such spin-exchange polarization transfer from optically-thin
species is useful in a variety of areas, including spin-polarized nuclear
scattering targets and electron beams, quantum-non-demolition spin
measurements, and ultra-sensitive magnetometry.

28
The categories of this paper are: alg-geom
35
The categories of this paper are: mtrl-th
26
The categories of this paper are: bayes-an
5
The categories of this paper are: gr-qc
19
The categories of this paper are: eess
15
The categories of this paper are: nucl-ex
10
The categories of this paper are: q-bio
8
The categories of this paper are: hep-ex
37
The categories of this paper are: supr-con
36
The categories of this paper are: cmp-lg
13
The categories of this paper are: quant-ph
17
The categories of this paper are: q-fin
33
The categories of this paper are: plasm-ph
25
The categories of this paper are: patt-sol
27
The categories of this paper are: comp-gas
16
The categories of this paper are: stat