Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Inversionless gain in a three-level system driven by a strong field and
  collisions   Inversionless gain in a three-level system driven by a strong external field
and by collisions with a buffer gas is investigated. The mechanism of
populating of the upper laser level contributed by the collision transfer as
well as by relaxation caused by a buffer gas is discussed in detail. Explicit
formulae for analysis of optimal conditions are derived. The mechanism
developed here for the incoherent pump could be generalized to other systems.

6
The categories of this paper are: astro-ph
21
The categories of this paper are: adap-org
33
The categories of this paper are: plasm-ph
27
The categories of this paper are: comp-gas
12
The categories of this paper are: nucl-th
22
The categories of this paper are: chao-dyn
29
The categories of this paper are: funct-an
11
The categories of this paper are: hep-lat
19
The categories of this paper are: eess
8
The categories of this paper are: hep-ex
34
The categories of this paper are: chem-ph
16
The categories of this paper are: stat
10
The categories of this paper are: q-bio
23
The categories of this paper are: solv-int
1
The categories of this paper are: cs
32
The categories of this paper are: atom-ph