Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Optical helicity of interfering waves   Helicity is a property of light which is familiar from particle physics but
less well-known in optics. In this paper we recall the explicit form taken by
the helicity of light within classical electromagnetic theory and reflect upon
some of its remarkable characteristics. The helicity of light is related to,
but is distinct from, the spin of light. To emphasise this fact, we draw a
simple analogy between the helicity of light and electric charge and between
the spin of light and electric current. We illustrate this and other
observations by examining various superpositions of plane waves explicitly.

27
The categories of this paper are: comp-gas
21
The categories of this paper are: adap-org
33
The categories of this paper are: plasm-ph
5
The categories of this paper are: gr-qc
15
The categories of this paper are: nucl-ex
20
The categories of this paper are: acc-phys
16
The categories of this paper are: stat
1
The categories of this paper are: cs
17
The categories of this paper are: q-fin
22
The categories of this paper are: chao-dyn
7
The categories of this paper are: hep-th
9
The categories of this paper are: nlin
18
The categories of this paper are: econ
8
The categories of this paper are: hep-ex
32
The categories of this paper are: atom-ph
24
The categories of this paper are: dg-ga