David Andrews leads nanophotonics and quantum electrodynamics research at UEA, where he has a Chair. The interests of his group include quantum and nonlinear optics, fundamental photonics, energy transport, optical manipulation and switching, and optical vortices. He has over 330 research papers and 15 books to his name, including a widely adopted textbook on Lasers in Chemistry and, as co-editor and contributor, a volume entitled The Angular Momentum of Light. David was elected a Fellow of the Institute of Physics in 1999, and a Fellow of SPIE, the International Society for Optical Engineering, in 2006. David has instigated and steered several conferences that are now well established, international meetings, including an annual Complex Light and Optical Forces conference in the States, and the biennial Nanophotonics conference in Europe, both now the largest of their kind. He has held two terms of office as Chair of the Molecular Spectroscopy Group, and he is now a member of the Board of Directors of SPIE, and Chair of its Symposia Committee. David enjoys frequent travels, and many other interests including painting and the graphic arts: in addition to landscapes he has produced cover art for several of his books and journal covers.

**Publications**(120)

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*Fluorescence Resonance Energy Transfer*(FRET), the most common mechanism for electronic energy to migrate between molecular chromophores, has a predominantly inverse sixth power dependence on the rate of transfer as a function of the distance R between the chromophores. However, the unified theory of electronic energy transfer, derived from

*quantum electrodynamics*, predicts an additional contribution with an

*R*dependence on distance. This intermediate-zone term becomes especially important when the chromophore spacing is similar in magnitude to the reduced wavelength (ƛ= λ 2π ) associated with the mediated energy. In previous theoretical studies we have suggested that inclusion of the intermediate term, through rate equation and quantum dynamical calculations, may be important for describing the exciton diffusion process in some circumstances, and in particular when the distance between the chromophores exceeds 5 nm. In this paper, we focus of the role of the intermediate-zone contribution to distance measurements between chromophores made through the application of

^{-4}*spectroscopic ruler*techniques. One of the major assumptions made in employing these experimental techniques is that the

*R*dependence is valid. In this work, we reformulate the spectroscopic ruler principles for intermediate distances to include the inverse fourth power rate component, and compare the results of this reformulation to experimental FRET results from the literature.

^{−6}^{3}, does not include the detail required to describe what is observed experimentally, in the absence of a static field. New results emerge upon extending the theory to include E1

^{2}E2 and E1

^{2}M1, incorporating one electric quadrupolar or magnetic dipolar interaction respectively. Both additional interactions require the deployment of higher orders in the multipole expansion to govern these processes, with the E1

^{2}E2 interaction analogous in rank and parity to a four-wave susceptibility. A key feature of the present work is its foundation upon a formal tensor derivation which does not oversimplify the molecular components, yet leads to results whose interpretation can be correlated with experimental observations. Results are summarized for the perpendicular detection of both parallel and perpendicular polarizations. Using such methods to investigate molecular systems that might have useful nonlinear characteristics, HRS therefore provides a route to data with direct physical interpretation, to enable more sophisticated design of molecules with sought optical properties.

*transfer fidelity*, signifying the accuracy of mapping input to designated output, is introduced and its key determinants are identified. Analysis shows that, at reasonable levels of laser intensity, cross-talk to unsought destinations can be effectively extinguished. The advantage of constructing these donor and acceptor thin-film layers around an ultra-thin spacer material (which is suitably transparent) is discussed, and potential applications beyond simple switching are outlined, including logic gates and optical buffers.

*l*units of orbital angular momentum per photon, and the steady-state saturation form of the torque is also determined by the width of the upper state in the atomic transition. It has been shown that, to leading order, the transfer of orbital angular momentum can only occur between the twisted light and the centre of mass motion. We argue here that, for small linewidth, the full time-dependence of the torque is needed to account correctly for the dynamics of atoms in a twisted light beam. We outline the theoretical framework needed to derive this full time-dependence, applying the theory to the motion in a twisted light beam of Eu

^{3+}ions, which possess a particularly narrow linewidth state. For relatively large linewidth, the steady-state forces and torque are appropriate, but the processes of cooling and trapping require the application of several suitably oriented twisted beams. The description of atomic motion in multiple twisted beams demands the application of special coordinate transformations. We show how to construct the appropriate transformation matrices to represent a twisted light beam propagating in an arbitrary direction, and we proceed to investigate the cooling and trapping of Mg

^{+}ions in sets of pairs of counter-propagating twisted beams in two-dimensional and three-dimensional molasses configurations.

Electronic coupling mechanisms and characteristics for optically nonlinear photoactive nanomaterials

^{-1}in the far infrared spectrum of diketopiperazine (DKP) is assigned to a ring puckering vibration. The multiplet structure reported for this band in the low temperature (77 K) far IR spectrum can be interpreted if the vibration is assumed to have quartic character. By means of Rayleigh-Schrodinger perturbation theory, a new vibrational selection rule, (Delta) n equals +/- 1, +/- 3, has been derived for mixed quartic-quadratic vibrations in the near harmonic region for the case of zero electrical anharmonicity. Assignments of the multiplet components have been made in the light of this vibrational selection rule. A two-parameter potential energy function of the ring puckering coordinate has been derived for the DKP molecule. This has enabled a value of ca. 355 cm

^{-1}to be estimated for the energy barrier to interconversion of enantiomeric boat forms of DKP. The 0 - 1 transition has been estimated to have a wavenumber value of 0.033 cm

^{-1}(1 GHz) in excellent agreement with the value of approximately 1 GHz obtained from a gas phase microwave spectroscopic study.

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