Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Collimated UV light generation by two-photon excitation to a Rydberg
  state in Rb vapor   We use two continuous-wave (CW) laser beams of 780 nm and 515 nm to optically
drive $^{85}$Rb atoms in a heated vapor cell to a low-lying Rydberg state
10D$_{5/2}$. We observe a collimated ultraviolet (UV) beam at 311 nm,
corresponding to the transition frequency from the 11P$_{3/2}$ state to the
5S$_{1/2}$ state. This indicates the presence of a coherent four-wave mixing
process, built up by two input laser fields as well as a terahertz (THz)
radiation of 3.28 THz that is generated by amplified spontaneous emission
between the 10D$_{5/2}$ and the 11P$_{3/2}$ states. We characterize the 311 nm
UV light generation and its dependence on various physical parameters. This
scheme could open up a new possibility for generating narrow-band THz waves as
well as deep UV radiation.

15
The categories of this paper are: nucl-ex
27
The categories of this paper are: comp-gas
30
The categories of this paper are: q-alg
25
The categories of this paper are: patt-sol
37
The categories of this paper are: supr-con
0
The categories of this paper are: hep-ph
10
The categories of this paper are: q-bio
18
The categories of this paper are: econ
7
The categories of this paper are: hep-th
2
The categories of this paper are: math
21
The categories of this paper are: adap-org
24
The categories of this paper are: dg-ga
32
The categories of this paper are: atom-ph
31
The categories of this paper are: ao-sci
11
The categories of this paper are: hep-lat
14
The categories of this paper are: math-ph