Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spatiotemporal helicon wavepackets   Propagation-invariant or non-diffracting optical beams have received
considerable attention during the last two decades. However, the pulsed nature
of light waves and the structured property of optical media like waveguides are
often overlooked. We here present a four-dimensional spatiotemporal approach
that extends and unifies both concepts of conical waves and helicon beams,
mainly studied in bulk media. By taking advantage of tight correlations between
the spatial modes, the topological charges, and the frequencies embedded in an
optical field, we reveal propagation-invariant (dispersion- and
diffraction-free) space-time wavepackets carrying orbital angular momentum
(OAM) that evolve on spiraling trajectories in both time and space in bulk
media or multimode fibers. Besides their intrinsic linear nature, we show that
such wave structures can spontaneously emerge when a rather intense ultrashort
pulse propagates nonlinearly in OAM modes. With emerging technologies of
pulse/beam shaping, multimode fibers and modal multiplexing, our proposed
scheme to create OAM-carrying helicon wavepackets could find a plethora of
applications.

1
The categories of this paper are: cs
16
The categories of this paper are: stat
26
The categories of this paper are: bayes-an
31
The categories of this paper are: ao-sci
4
The categories of this paper are: cond-mat
21
The categories of this paper are: adap-org
11
The categories of this paper are: hep-lat
20
The categories of this paper are: acc-phys
8
The categories of this paper are: hep-ex
33
The categories of this paper are: plasm-ph
28
The categories of this paper are: alg-geom
10
The categories of this paper are: q-bio
30
The categories of this paper are: q-alg
32
The categories of this paper are: atom-ph
9
The categories of this paper are: nlin
19
The categories of this paper are: eess