Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Angular momentum of circularly polarized light in dielectric media   A circularly polarized plane-wave is known to have no angular momentum when
examined through Maxwell's equations. This, however, contradicts the
experimentally observed facts, where finite segments of plane waves are known
to be capable of imparting angular momentum to birefringent platelets. Using a
superposition of four plane-waves propagating at slightly different angles to a
common direction, we derive an expression for the angular momentum density of a
single plane-wave in the limit when the propagation directions of the four
beams come into alignment. We proceed to use this four-beam technique to
analyze the conservation of angular momentum when a plane-wave enters a
dielectric slab from the free space. The angular momentum of the beam is shown
to decrease upon entering the dielectric medium, by virtue of the fact that the
incident beam exerts a torque on the slab surface at the point of entry. When
the beam leaves the slab, it imparts an equal but opposite torque to the exit
facet, thus recovering its initial angular momentum upon re-emerging into the
free-space. Along the way, we derive an expression for the outward-directed
force of a normally incident, finite-diameter beam on a dielectric surface; the
possible relationship between this force and the experimentally observed
bulging of a liquid surface under intense illumination is explored.

20
The categories of this paper are: acc-phys
33
The categories of this paper are: plasm-ph
9
The categories of this paper are: nlin
23
The categories of this paper are: solv-int
11
The categories of this paper are: hep-lat
13
The categories of this paper are: quant-ph
24
The categories of this paper are: dg-ga
29
The categories of this paper are: funct-an
5
The categories of this paper are: gr-qc
26
The categories of this paper are: bayes-an
2
The categories of this paper are: math
32
The categories of this paper are: atom-ph
31
The categories of this paper are: ao-sci
35
The categories of this paper are: mtrl-th
28
The categories of this paper are: alg-geom
10
The categories of this paper are: q-bio