Interaction of flying electromagnetic doughnut with nanostructures

We report on the electromagnetic properties of the single-cycle "flying doughnut" electromagnetic permutations in the context of their interactions with nanoscale objects, such as dielectric and plasmonic nanoparticles

Interrogating nanoparticles with focused doughnuts

The propagation of electromagnetic radiation in free-space is described by the source-free Maxwells equations. In contrast to conventional solutions such as infinite-energy plane waves and Gaussian pulses, there exists a family of exact solutions which represent localised transmission of finite electromagnetic energy [1]. One such solution is known as the Focused Doughnut (FD) pulse a peculiar single-cycle electromagnetic perturbation with a unique toroidal field topology and 3-dimensional, polynomial energy localisation [2]. Here, for the first time we present a comprehensive study of the FD pulse: we investigate the propagation dynamics and interactions of these complex electromagnetic pulses with homogeneous and structured media.The FD pulse exhibits a number of intriguing properties. Its purely single-cycle nature results in an ultra-broadband frequency spectrum and a well defined spatial-chirp. In fact, the spatial dependence of the pulse is inseparable from its temporal dependence. In addition, the toroidal topology of the pulse gives rise to significant longitudinal field components at the pulse that hold potential for particle acceleration applications [2]. Although the FD pulse has remained a theoretical curiosity since its first prediction, successful experimental realisation could lead to its use in a variety of settings, such as microscopy, communications, directed energy transfer, spectroscopy, and particle trapping and acceleration. Further interest in the FD pulse stems from the burgeoning field of toroidal electrodynamics, owing to the topological similarities between the FD pulse and the near-field configuration of the toroidal dipole excitation [3].The intriguing light-matter interactions of the FD pulse are examined from several perspectives. We present a full evaluation of the transformations the FD pulse undergoes due to interactions with dielectric and metallic interfaces. This has revealed the unusual behaviour of both the TE and TM pulses under reflection, with respect to the reversal of the azimuthal and radial field components. Furthermore, the interactions of FDs with small dielectric and plasmonic particles are considered, where the broadband nature and complex field topology of the pulses is expected to play a significant role in mode excitation. Recent work has demonstrated broad modal excitation within the nanostructures and distinct differences between the interaction with TE and TM pulses. Possible experimental realisations of these complex electromagnetic perturbations resulting from the theoretical/computational treatment presented here will be discussed

Generation of flying electromagnetic doughnuts via spatiotemporal conversion of transverse electromagnetic pulses

We introduce a new class of metamaterials that allow simultaneous spatial and temporal control of electromagnetic waveforms and present for the first time the generation of flying doughnuts, single-cycle pulses of toroidal topology

A new type of optical activity in a toroidal metamaterial

We demonstrate experimentally and numerically the first ever observation of optical activity in a chiral metamaterial that is underpinned by the exotic resonant combination of an electric quadrupole and the elusive toroidal dipole

Toroidal circular dichroism

We demonstrate that the induced toroidal dipole, represented by currents flowing on the surface of a torus, makes a distinct and indispensable contribution to circular dichroism. We show that toroidal circular dichroism supplements the well-known mechanism involving electric dipole and magnetic dipole transitions. We illustrate this with rigorous analysis of the experimentally measured, polarization-sensitive transmission spectra of an artificial metamaterial, constructed from elements of toroidal symmetry. We argue that toroidal circular dichroism shall be found in large biomolecules with elements of toroidal symmetry and should be taken into account in the interpretation of circular dichroism spectra of organics

Focused electromagnetic doughnut pulses and their interaction with interfaces and nanostructures

We study the propagation properties and light-matter interactions of the focused doughnut pulses, broadband, single-cycle electromagnetic perturbations of toroidal topology first described by Hellwarth and Nouchi in 1996. We show how focused doughnuts are reflected and refracted at planar metallic and vacuum-dielectric interfaces leading to complex distortions of the field structure. We also identify the conditions under which these toroidal pulses excite dominant dynamic toroidal dipoles in spherical dielectric particles

Interrogating nanoparticles with focused doughnut pulses

We study the propagation properties of space-time localized single-cycle waveforms of toroidal symmetry and report on their light-matter interactions with interfaces and nanoparticles

New enantiomeric phenomena in toroidal media

Optical activity is a phenomenon ubiquitous across natural and artificial structures and is generally understood in terms of the coupling between electric and magnetic dipoles [1]. Usually, this dipole approximation is sufficient to explain optical activity in most media. In metamaterials however, engineering of the structure allows for designs where a conventional multipole (electric and magnetic dipole) response is suppressed in favour of more exotic excitations typically excluded from the standard multipole expansion. Here, we report on the first computational study of optical activity in a metamaterial that cannot be attributed to conventional multipoles, and can only be accounted for by the inclusion of the toroidal dipole