The development of metamaterials operating at visible light wavelengths requires metamaterials to be produced with nanoscale structure over large areas. Improvements in the efficiency of electron beam lithography (EBL) could play an important role in accelerating this development. In this paper we show the production of a shaped probe for use in EBL. A phase structured electron wave containing vortices can be focused to produce a C-shaped cross section. Local spatial frequency analysis shows that both the gap and overall size of the C-shape can be easily controlled. We present the generation of such a C-shaped electron beam using a holographic binary amplitude diffraction mask. Thin AlF3 film is exposed to the C-shaped diffraction order and demonstrates the facile production of both a metallic C-shaped structure as well as the etching of a C-shaped hole.
The total internal reflection of an optical beam with a phase singularity can generate evanescent light that displays a
rotational character. At a metalized surface, in particular, field components extending into the vacuum region possess
vortex properties in addition to surface plasmon features. These surface plasmonic vortices retain the phase singularity
of the input light, also mapping its associated orbital angular momentum. In addition to a two-dimensional patterning on
the surface, the strongly localized intensity distribution decays with distance perpendicular to the film surface. The
detailed characteristics of these surface optical vortex structures depend on the incident beam parameters and the
dielectric mismatch of the media. The static interference of the resulting surface vortices, achieved by using beams
suitably configured to restrict lateral in-plane motion, can be shown to give rise to optical forces that produce interesting
dynamical effects on atoms or small molecules trapped in the vicinity of the surface. As well as trapping within the
surface plasmonic fields, model calculations reveal that the corresponding atomic trajectories will typically exhibit a
variety of rotational and vibrational effects, significantly depending on the extent and sign of detuning from resonance.
It is well established that the presence of interfaces separating regions of real space that are occupied by different
materials, has given rise to a wealth of new phenomena and a number of significant applications. It is therefore
evident that surfaces must feature prominently in the physics of structures at the small scale and the influence of such
structures on the properties of quantum systems in their vicinity. This article is concerned with a structure created
using two surfaces forming an open cavity, and we concentrate on the right-angle geometry. Although apparently
simple, this structure adequately serves to illustrate the essential physics, which turns out to be surprisingly complex
when one considers correlations. We discuss how excited quantum emitters localized within this open cavity, and
which can be manipulated optically, would discharge the excitation, both when the emitters are in isolation from other
similar emitters and when taken in pairs. Quantum correlations of this kind are essential in the context of
implementing scalable architectures for quantum information processing and quantum computing. Optical
manipulation near surfaces is one possible scenario that has been highlighted in that context.
The properties of localised dipole emitters in the form of a quantum dot or a colour centre embedded in a crystal
environment can be drastically modified by a change in the composition, size and shape of the environment in
which the emitter is embedded. Thanks to recent advances in material deposition techniques and lithography,
as well as the advances in detection techniques and optical manipulation, experimental work is now capable of
revealing a new range of physical phenomena when the typical dimensions are of the order of an optical dipole
transition wavelength and below. These advances have arisen at a time of a heightened research effort devoted to
the important goal of identifying a qubit and a suitable environment that forms the basis for a scalable hardware
architecture for the practical realisation of quantum information processing. A physical system that we have
recently put forward as a candidate for such a purpose involves localised emitters in the form of quantum dots
or colour centres embedded in a nanocrystal. This suggestion became more persuasive following the success of
experiments which, for the first time, were able to demonstrate quantum cryptography using a nitrogen vacancy
in a diamond nanocrystal as a single-photon source. It has, however, been realised that a more versatile scenario
could be achieved by making use of the interplay between dielectric cavity confinement and dipole orientation.
Besides position dependence the main properties exhibit strong dipole orientational dependece suggesting that the
system is a possible candidate as a qubit for a scalable hardward architecture for quantum information processing.
Cavity confinement can control processes since it can lead to the enhancement and the complete suppression of
the de-excitation process, with further control provided by the manipulation of the dipole orientation by optical
means. This article is concerned with the modelling of quantum processes for quantum systems localised in
artificially fabricated structures made of high conductivity metals and dielectric cavities. The essential features
of cavity field confinement in this context are presented and the effects on de-excitation rates are assessed.
Theoretical work has already established the existence of a light-induced torque acting on the centre of mass of an atom, ion or molecule immersed in twisted light, where the transition frequency is suitably detuned from that of the twisted light beam. The twisted beam carries 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 Eu3+ 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.
We examine novel features that might emerge from the interaction of Laguerre-Gaussian beams with liquid crystals. We study the response of nematic liquid crystal media to the throughput of twisted laser light. Specific attention is focused on the spatial evolution of the director orientation angle.
In recent years, twisted laser beams and optical vortices have attracted considerable interest, in terms of both their fundamental quantum properties and also their potential technical applications. Here we examine what novel features might emerge from the interaction of such beams with chiral matter. In this connection we assess the possible scope for exploiting similarities between the angular momentum properties of circularly polarised light and optical vortices - both with regard to their mechanical torque and also the associated spectroscopic selection rules. Twisted beams have generally been studied only in their interactions with achiral matter, with the theory largely developed for electric dipole coupling. In chiral systems, the low symmetry enables many optical transitions to be allowed under the selection rules for both electric and magnetic multipoles, and the entanglement of spin and orbital photon angular momentum requires careful extrication. Specific issues to be addressed are: what new features, if any, can be anticipated when such beams are used to interrogate a chiral system, and whether in such cases enantiomeric specificity can be expected. To this end we develop theory that goes to a higher order of multipole expansion, also engaging magnetic dipole and electric quadrupole transitions. Finally, we study the response of nematic liquid crystal media to the throughput of twisted laser light. Specific attention is focused on the spatial evolution of the director orientation angle.
The propensity of conventional optical beams to convey angular momentum is very well known. As a spin-1 elementary particle any photon can assume a polarisation state with a well defined 'spin' angular momentum of plus or minus 1 in the direction of propagation, corresponding to a circular polarisation of either left or right helicity. The mechanical effects of photonic angular momentum are manifest in a variety of phenomena operating at both the atomic and macroscopic scale. Photon angular momentum also exercises a key role in atomic spectroscopy and a host of other fundamental optical phenomena.
The aim of this work is to study the interaction between matter and Laguerre-Gaussian beams, and others of related structure in which a helical wavefront confers an endowment with 'orbital' angular momentum. Although the principles and methods of production of these twisted beams are already quite well understood, the detailed study of the interactions is a novel subject. We explore changes in selection rules transfer of linear and angular momentum in the context of nonlinear processes, especially harmonic and sum-frequency generation.