Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Nonlinear envelope equation for broadband optical pulses in quadratic
  media   We derive a nonlinear envelope equation to describe the propagation of
broadband optical pulses in second order nonlinear materials. The equation is
first order in the propagation coordinate and is valid for arbitrarily wide
pulse bandwidth. Our approach goes beyond the usual coupled wave description of
$\chi^{(2)}$ phenomena and provides an accurate modelling of the evolution of
ultra-broadband pulses also when the separation into different coupled
frequency components is not possible or not profitable.

19
The categories of this paper are: eess
12
The categories of this paper are: nucl-th
29
The categories of this paper are: funct-an
28
The categories of this paper are: alg-geom
1
The categories of this paper are: cs
7
The categories of this paper are: hep-th
35
The categories of this paper are: mtrl-th
36
The categories of this paper are: cmp-lg
17
The categories of this paper are: q-fin
0
The categories of this paper are: hep-ph
37
The categories of this paper are: supr-con
34
The categories of this paper are: chem-ph
4
The categories of this paper are: cond-mat
32
The categories of this paper are: atom-ph
27
The categories of this paper are: comp-gas
10
The categories of this paper are: q-bio