L. Allen

Les Allen became a laser physicist in 1960/1961, soon after completing his PhD in atomic spectroscopy. Since then has worked in quantum optics and optical physics. His detailed experimental analysis of the Lamb theory of the laser was conducted in the 1960s at Sussex, after which he began to investigate Amplified Spontaneous Emission (ASE) and its relationship to superradiance in considerable depth. Interest in other coherent phenomena led to his authoring the much cited book "Optical Resonance and Two-level Atoms" (Dover) with J. H. Eberly. A significant period was then spent examining multi-photon processes, after which he spent five years away from research in senior academic administration. Since 1991 he enjoyed a peripatetic existence at Leiden, Utrecht and JILA, Colorado, with Visiting Professorships at Essex and St Andrews, and was awarded two Leverhulme Fellowships. He also co-ordinated the SERC "Nonlinear Optics Initiative" from 1992-1994. His current affiliations are Visiting Professor at the Universities of Strathclyde and Sussex and Honorary Research Fellow, University of Glasgow.

On his return to physics in 1991 he ceased to be an experimental physicist closely connected with theory and became a theoretician. Most of his recent work has been concerned with the orbital angular momentum of the photon and its manifestation in readily realisable laboratory light beams. Such beams are closely analogous in many respects to those which are circularly polarised, although polarisation is associated with spin angular momentum and the intrinsic spin of the photon. A matrix formulation equivalent to the Jones matrices has been established for orbital angular momentum. Cooling and trapping of atoms with light beams possessing orbital angular momentum has been investigated and an azimuthal Doppler shift, and a possible manifestation of spin-orbit coupling of the photon predicted.

The work on orbital angular momentum has been done initially with Woerdman at Leiden, but most of it with Mohamed Babiker at Essex, Miles Padgett at St Andrews and Glasgow and with Steve Barnett at Strathclyde. This area of physics is fully documented in a monograph entitled "Optical Angular Momentum" (IOPP, 2003) co-authored with Barnett and Padgett. The book reproduces 44 key original papers including 17 of his own, arranged in 8 Sections each prefaced with a succinct introduction. The work, and that of others, is also summarised in "Progress in Optics" XXXIX (Ed: Wolf), 294-372, 1999 and J.Opt.B: Quantum Semiclass. Opt. 4, S1-6, 2002.

In addition to some 120 papers and the above volume, Allen has written one book and co-authored three others on laser physics and quantum optics. The absence of formal academic duties has allowed his exclusive involvement with research over the last decade and more.

The same freedom has, over the last 5 years, also allowed a return to painting for the first time since he was young. His acrylic on canvas paintings, strongly influenced by the Abstract Expressionists, have been exhibited and sold in the Suffolk Open Studios exhibitions and in Penrith, Cumbria. His most recent work includes the development of a series of mixed media monoprints.