Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Propagation of ultrashort electromagnetic wave packets in free space
  beyond the paraxial and slowly-varying-envelope approximations : a
  time-domain approach   A time-domain approach is proposed for the propagation of ultrashort electro-
magnetic wave packets beyond the paraxial and the slowly-varying-envelope
approximations. An analytical method based on perturbation theory is used to
solve the wave equation in free space without resorting to Fourier trans-
forms. An exact solution is obtained in terms of successive temporal and
spatial derivatives of a monochromatic paraxial beam. The special case of a
radially polarized transverse magnetic wave packet is discussed.

1
The categories of this paper are: cs
11
The categories of this paper are: hep-lat
22
The categories of this paper are: chao-dyn
23
The categories of this paper are: solv-int
10
The categories of this paper are: q-bio
34
The categories of this paper are: chem-ph
27
The categories of this paper are: comp-gas
29
The categories of this paper are: funct-an
5
The categories of this paper are: gr-qc
8
The categories of this paper are: hep-ex
25
The categories of this paper are: patt-sol
2
The categories of this paper are: math
21
The categories of this paper are: adap-org
31
The categories of this paper are: ao-sci
36
The categories of this paper are: cmp-lg
28
The categories of this paper are: alg-geom