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[ Interferogram of a high-order optical vortex ]
The telltale signs of the vortex are the whirling pattern and the high intensity peaks in
concentric circles, which correspond to the angular variation of the transverse phase.
Because optical vortices are located where the field is exactly zero, they can be
detected using interference to uncover their characteristic phase circulation.
performance of these algorithms relies
strongly on the accurate calculation of
two-dimensional phase maps.
The values of the phase around a vortex can actually circulate more than once
from 0 to 2p, and the number of turns
is referred to as the topological charge of
the vortex. Interestingly, however, vortices with a charge magnitude higher than
one rarely occur in the aforementioned
cases. The incidence of vortices is thus
largely regarded as a nuisance, since they
can make the accurate reconstruction
of the phase maps difficult or impossible. The characteristic phase circulation
around vortices is generally evidence of
an important property of the field: its
orbital angular momentum.
Optical vortices are useful in several
applications. In astrophysics, introducing vortex-forming optics in the path of
an astronomical telescope can help to
resolve closely spaced stars, providing
a tool for detecting extra-solar planets. Researchers have also induced the
formation of vortices in an ultra-cold
gas by stirring it; this allows them to
study and demonstrate its super-fluidity.
More recently, vortices embedded in a
laser beam have been transferred to cold
atoms so that researchers can study how
circulation currents persist in the form of
coherent matter waves in these strongly
interacting ensembles of atoms.