Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Coherent combining of self-cleaned multimode beams   A low intensity light beam emerges from a graded-index, highly multimode
optical fibre with a speckled shape, while at higher intensity the Kerr
nonlinearity may induce a spontaneous spatial self-cleaning of the beam [1,2].
Here, we reveal that we can generate two self-cleaned beams with a mutual
coherence large enough to produce a clear stable fringe pattern at the output
of a nonlinear interferometer. The two beams are pumped by the same input
laser, yet are self-cleaned into independent multimode fibres. We thus prove
that the self-cleaning mechanism preserves the beams' mutual coherence via a
noise-free parametric process. While directly related to the initial pump
coherence, the emergence of nonlinear spatial coherence is achieved without
additional noise, even for self-cleaning obtained on different modes, and in
spite of the fibre structural disorder originating from intrinsic imperfections
or external perturbations. Our discovery may impact theoretical approaches on
wave condensation [3-5], and open new opportunities for coherent beam combining
[6-9].

30
The categories of this paper are: q-alg
4
The categories of this paper are: cond-mat
22
The categories of this paper are: chao-dyn
24
The categories of this paper are: dg-ga
15
The categories of this paper are: nucl-ex
29
The categories of this paper are: funct-an
35
The categories of this paper are: mtrl-th
10
The categories of this paper are: q-bio
32
The categories of this paper are: atom-ph
6
The categories of this paper are: astro-ph
25
The categories of this paper are: patt-sol
14
The categories of this paper are: math-ph
9
The categories of this paper are: nlin
0
The categories of this paper are: hep-ph
28
The categories of this paper are: alg-geom
33
The categories of this paper are: plasm-ph