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

Fedotov, V.A.

Papasimakis, N.

Raybould, T.A.

Youngs, I.

Zheludev, N.I.

Southampton (e-Prints Soton)

Interrogating Nanoparticles with Focused Doughnut Pulses T. A. Raybould1, V. A. Fedotov1, N. Papasimakis1,*, I. Youngs2, N. I. Zheludev1,3  1Optoelectronics Research Centre, University of Southampton, Southampton, United Kingdom 2DSTL, Salisbury, United Kingdom 3Centre for Disruptive Photonic Technologies, Nanyang Technological University, Singapore  *np3@orc.soton.ac.uk  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.   Focused doughnut (FD) pulses are part of a family of exact solutions to Maxwell’s equations representing localised transmission of finite electromagnetic energy [1,2]. These are single-cycle pulses with toroidal field topology and polynomial energy localisation (Fig.1a) [2]. They exhibit an ultra-broadband frequency spectrum, which varies spatially. In addition, the toroidal topology of the pulse gives rise to significant longitudinal field components that hold potential for particle acceleration [2], but also resemble the field configuration associated with the toroidal dipole moment [3]. Here, we present a computational study of the FD pulse propagation properties and its interactions with dielectric and metallic interfaces, revealing unusual behaviour under reflection. Furthermore, the interactions of FDs with dielectric particles are considered, where the broadband nature and complex field topology of the pulses is expected to control mode excitation. Recent work has demonstrated broad modal excitation within the nanostructures and distinct differences between the interaction with TE and TM pulses (Fig. 1c). Possible experimental realisations of these complex electromagnetic perturbations resulting from the theoretical/computational treatment presented here will be discussed.  Fig. 1. (a) Illustration of the field topology and focusing properties of a TE FD pulse propagating along the z-axes. (b) Ex (upper) and Hz (lower) fields of the FD pulse with q1 denoting the effective wavelength. (c) Excitation spectrum for a non-dispersive, dielectric nanoparticle (r=q1) under FD illumination.  References [1] R. W. Ziolkowski, Localised transmission of electromagnetic energy, Phys. Rev. A 39, 2005 (1989) [2] R. W. Hellwarth, P. Nouchi, Focused one-cycle electromagnetic pulses, Phys. Rev. E 54, 889 (1993) [3] T. Kaelberer et al., Toroidal dipolar response in a metamaterial, Science 330, 1510  (2010) 

Interrogating nanoparticles with focused doughnut pulses

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