Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Fractal light from lasers   Fractals, complex shapes with structure at multiple scales, have long been
observed in Nature: as symmetric fractals in plants and sea shells, and as
statistical fractals in clouds, mountains and coastlines. With their highly
polished spherical mirrors, laser resonators are almost the precise opposite of
Nature, and so it came as a surprise when, in 1998, transverse intensity
cross-sections of the eigenmodes of unstable canonical resonators were
predicted to be fractals [Karman et al., Nature 402, 138 (1999)]. Experimental
verification has so far remained elusive. Here we observe a variety of fractal
shapes in transverse intensity cross-sections through the lowest-loss
eigenmodes of unstable canonical laser resonators, thereby demonstrating the
controlled generation of fractal light inside a laser cavity. We also advance
the existing theory of fractal laser modes, first by predicting 3D self-similar
fractal structure around the centre of the magnified self-conjugate plane,
second by showing, quantitatively, that intensity cross-sections are most
self-similar in the magnified self-conjugate plane. Our work offers a
significant advance in the understanding of a fundamental symmetry of Nature as
found in lasers.

23
The categories of this paper are: solv-int
15
The categories of this paper are: nucl-ex
25
The categories of this paper are: patt-sol
19
The categories of this paper are: eess
17
The categories of this paper are: q-fin
24
The categories of this paper are: dg-ga
20
The categories of this paper are: acc-phys
31
The categories of this paper are: ao-sci
0
The categories of this paper are: hep-ph
2
The categories of this paper are: math
26
The categories of this paper are: bayes-an
1
The categories of this paper are: cs
12
The categories of this paper are: nucl-th
36
The categories of this paper are: cmp-lg
16
The categories of this paper are: stat
37
The categories of this paper are: supr-con