  While photons travel in a straight line at constant velocity in free-space,
the intensity profile of structured light may be tailored for acceleration in
any degree of freedom. Here we propose a simple approach to control the angular
acceleration of light. Using Laguerre-Gaussian modes as our twisted beams
carrying orbital angular momentum, we show that superpositions of opposite
handedness result in a radially dependent angular acceleration as they pass
through a focus (waist plane). Due to conservation of orbital angular momentum
we find that propagation dynamics are complex despite the free-space medium:
the outer part of the beam (rings) rotates in an opposite direction to the
inner part (petals), and while the outer part accelerates so the inner part
decelerates. We outline the concepts theoretically and confirm them
experimentally. Such exotic structured light beams are topical due to their
many applications, e.g., optical trapping and tweezing, metrology and
fundamental studies in optics.

Optics