Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Generation of radiation in free electron lasers with diffraction
  gratings (photonic crystal) with the variable spacial period   The equations providing to describe generation process in FEL with varied
parameters of diffraction grating (photonic crystal) are obtained. It is shown
that applying diffraction gratings (photonic crystal) with the variable period
one can significantly increase radiation output. It is mentioned that
diffraction gratings (photonic crystal) can be used for creation of the
dynamical wiggler with variable period in the system. This makes possible to
develop double-cascaded FEL with variable parameters changing, which efficiency
can be significantly higher that of conventional system.

23
The categories of this paper are: solv-int
26
The categories of this paper are: bayes-an
25
The categories of this paper are: patt-sol
28
The categories of this paper are: alg-geom
1
The categories of this paper are: cs
14
The categories of this paper are: math-ph
15
The categories of this paper are: nucl-ex
9
The categories of this paper are: nlin
22
The categories of this paper are: chao-dyn
6
The categories of this paper are: astro-ph
31
The categories of this paper are: ao-sci
8
The categories of this paper are: hep-ex
29
The categories of this paper are: funct-an
32
The categories of this paper are: atom-ph
16
The categories of this paper are: stat
4
The categories of this paper are: cond-mat