2009 Young medal and prize

Professor Leslie Allen and Professor Miles Padgett

University of Glasgow

In recognition of their pioneering work on optical angular momentum.

Kepler deduced from the sun’s role in shaping comets’ tails that light carries linear momentum. Although mathematically embedded in Maxwell’s equations, it is only recently, thanks to the seminal work of Allen and Padgett that researchers have recognised and taken advantage of the full properties of light’s angular momentum.

In the 1930’s Beth showed that light carried spin angular momentum, but it was not until 1992 that light’s orbital angular momentum was elucidated by Allen and co-workers. Since then Allen and Padgett have pioneered both theoretical and experimental approaches to investigate virtually all aspects of light’s angular momentum.

They succeeded in converting optical tweezers into optical spanners, using light to rotating microscopic objects; this showed the mechanical equivalence of light’s spin and orbital angular momentum and has inspired much work in optical manipulation. Earlier there had been a study of this light’s interaction with atoms. Working together,they recognised the role that light’s orbital angular momentum plays in harmonic generation; a precursor to high-dimensional quantum entanglement. The phenomenology of orbital angular momentum encompasses geometric phases, rotational Doppler shift, angular uncertainly relationships and other topological features. It has been demonstrated that spin, orbital and total angular momentum can be measured for single photons and the increased data capacity utilised in a free space optical link.