Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Generation of Coherent Extreme-Ultraviolet Radiation Carrying Orbital
  Angular Momentum   We propose an effective scheme for the generation of intense coherent extreme
ultraviolet light beams carrying orbital angular momentum (OAM). The light is
produced by a high-gain harmonic-generation free-electron laser (FEL), seeded
using a laser pulse with a transverse staircase-like phase pattern. During
amplification, diffraction and mode selection drive the radiation profile
towards a dominant OAM mode at saturation. With a seed laser at 260 nm,
gigawatt power levels are obtained at wavelengths approaching those of soft
x-rays. Compared to other proposed schemes to generate OAM with FELs, our
approach is robust, easier to implement, and can be integrated into already
existing FEL facilities without extensive modifications of the machine layout.

34
The categories of this paper are: chem-ph
2
The categories of this paper are: math
31
The categories of this paper are: ao-sci
15
The categories of this paper are: nucl-ex
10
The categories of this paper are: q-bio
35
The categories of this paper are: mtrl-th
4
The categories of this paper are: cond-mat
13
The categories of this paper are: quant-ph
9
The categories of this paper are: nlin
19
The categories of this paper are: eess
16
The categories of this paper are: stat
14
The categories of this paper are: math-ph
24
The categories of this paper are: dg-ga
21
The categories of this paper are: adap-org
1
The categories of this paper are: cs
29
The categories of this paper are: funct-an