The interaction of light's orbital angular momentum (OAM) with matter has still several unexplored aspects. In
particular, it is unknown if there exists for OAM an effect analogous to spin angular momentum-based optical
activity. Here we study experimentally the influence of OAM on the interaction of light with a cholesteric liquid
crystal polymer. We use strongly focussed light where the polarization and the orbital degrees of freedom are
coupled. Two possible manifestations of an OAM-sensitive interaction are investigated: (i) the modification of
circular dichroism, and (ii) the occurrence of intermodal dispersion of the {l = +1, l = -1} modes. We conclude
that such an interaction does not exist within the experimental parameter range studied here.
High-dimensional entangled photons pairs are interesting for quantum information and cryptography: Compared
to the well-known 2D polarization case, the stronger non-local quantum correlations could improve noise resistance
or security, and the larger amount of information per photon increases the available bandwidth. One
implementation is to use entanglement in the spatial degree of freedom of twin photons created by spontaneous
parametric down-conversion, which is equivalent to orbital angular momentum entanglement, this has been
proven to be an excellent model system. The use of optical fiber technology for distribution of such photons
has only very recently been practically demonstrated and is of fundamental and applied interest. It poses a
big challenge compared to the established time and frequency domain methods: For spatially entangled photons,
fiber transport requires the use of multimode fibers, and mode coupling and intermodal dispersion therein
must be minimized not to destroy the spatial quantum correlations. We demonstrate that these shortcomings
of conventional multimode fibers can be overcome by using a hollow-core photonic crystal fiber, which follows
the paradigm to mimic free-space transport as good as possible, and are able to confirm entanglement of the
fiber-transported photons. Fiber transport of spatially entangled photons is largely unexplored yet, therefore we
discuss the main complications, the interplay of intermodal dispersion and mode mixing, the influence of external
stress and core deformations, and consider the pros and cons of various fiber types.
We present experiments on Orbital Angular Momentum (OAM) induced beam shifts in optical reflection. Specifically,
we observe the spatial Goos-Hänchen shift in which the beam is displaced parallel to the plane of incidence and the
angular Imbert-Fedorov shift which is a transverse angular deviation from the geometric optics prediction. Experimental
results agree well with our theoretical predictions. Both beam shifts increase with the OAM of the beam; we have
measured these for OAM indices up to 3. Moreover, the OAM couples these two shifts. Our results are significant for
optical metrology since optical beams with OAM have been extensively used in both fundamental and applied research.
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