11 research outputs found
Optical properties of radially-polarised twisted light
We show that, in general, any type of radially-polarised paraxial twisted
optical mode carries only an axial total optical angular momentum (AM) where is the winding number and
is a constant. This mode, however, is shown to have zero spin angular momentum
(SAM), so it is endowed only with orbital angular momentum (OAM) and no SAM.
The helicity is found to be proportional to , hence radially-polarised
modes display chirality. When applied to a Laguerre-Gaussian (LG) mode our
treatment leads to a total helicity equal to , where
is the action constant. The factor , depends on
the sign, not the magnitude of and so the result holds for any
radially-polarised LG mode however large the magnitude of its winding number
is. The magnitude of the action constant and hence the
helicity are diminished for all such LG modes of large beam waist .Comment: 4 figure
Radiation pattern of two identical emitters driven by a Laguerre-Gaussian beam: An atom nanoantenna
We study the directional properties of a radiation field emitted by a
geometrically small system composed of two identical two-level emitters located
at short distances and driven by an optical vortex beam, a Laguerre-Gaussian
beam which possesses a structured phase and amplitude. We find that the system
may operate as a nanoantenna for controlled and tunable directional emission.
Polar diagrams of the radiation intensity are presented showing that a constant
phase or amplitude difference at the positions of the emitters plays an
essential role in the directivity of the emission. We find that the radiation
patterns may differ dramatically for different phase and amplitude differences
at the positions of the emitters. As a result the system may operate as a two-
or one-sided nanoantenna. In particular, a two-sided highly focused directional
emission can be achieved when the emitters experience the same amplitude and a
constant phase difference of the driving field. We find a general directional
property of the emitted field that when the phase differences at the positions
of the emitters equal an even multiple of \pi/4, the system behaves as a
two-sided antenna. When the phase difference equals an odd multiple of \pi/4,
the system behaves as an one-sided antenna. The case when the emitters
experience the same phase but different amplitudes of the driving field is also
considered and it is found that the effect of different amplitudes is to cause
the system to behave as a uni-directional antenna radiating along the
interatomic axis.Comment: published versio
Quantum Hall Physics with Cold Atoms in Cylindrical Optical Lattices
We propose and study various realizations of a Hofstadter-Hubbard model on a
cylinder geometry with fermionic cold atoms in optical lattices. The
cylindrical optical lattice is created by copropagating Laguerre-Gauss beams,
i.e.~light beams carrying orbital angular momentum. By strong focusing of the
light beams we create a real space optical lattice in the form of rings, which
are offset in energy. A second set of Laguerre-Gauss beams then induces a
Raman-hopping between these rings, imprinting phases corresponding to a
synthetic magnetic field (artificial gauge field). In addition, by rotating the
lattice potential, we achieve a slowly varying flux through the hole of the
cylinder, which allows us to probe the Hall response of the system as a
realization of Laughlin's thought experiment. We study how in the presence of
interactions fractional quantum Hall physics could be observed in this setup.Comment: 10 pages, 9 figure