  Singular beams have attracted great attention due to their optical properties
and broad applications from light manipulation to optical communications.
However, there has been a lack of practical schemes with which to achieve
switchable singular beams with sub-wavelength resolution using ultrathin and
flat optical devices. In this work, we demonstrate the generation of switchable
vector and vortex beams utilizing dynamic metasurfaces at visible frequencies.
The dynamic functionality of the metasurface pixels is enabled by the
utilization of magnesium nanorods, which possess plasmonic reconfigurability
upon hydrogenation and dehydrogenation. We show that switchable vector beams of
different polarization states and switchable vortex beams of different
topological charges can be implemented through simple hydrogenation and
dehydrogenation of the same metasurfaces. Furthermore, we demonstrate a
two-cascade metasurface scheme for holographic pattern switching, taking
inspiration from orbital angular momentum-shift keying. Our work provides an
additional degree of freedom to develop high-security optical elements for
anti-counterfeiting applications.
