76 research outputs found
Helicity and duality symmetry in light matter interactions: Theory and applications
In my thesis, I first develop the theoretical basis and tools for the use of
helicity and duality in the study, understanding and engineering of
interactions between electromagnetic radiation and material systems. Then,
within the general framework of symmetries and conservation laws, I apply the
theoretical results to several different problems: Optical activity, zero
backscattering, metamaterials for transformation optics and nanophotonics
phenomena involving the electromagnetic angular momentum. The tool has provided
new insights and design guidelines in all these cases.Comment: PhD Thesis, Department of Physics and Astronomy, Macquarie
University. Fixed a very slow figure from the previous versio
On the dynamic toroidal multipoles from localized electric current distributions
We analyze the dynamic toroidal multipoles and prove that they do not have an
independent physical meaning with respect to their interaction with
electromagnetic waves. We analytically show how the split into electric and
toroidal parts causes the appearance of non-radiative components in each of the
two parts. These non-radiative components, which cancel each other when both
parts are summed, preclude the separate determination of each part by means of
measurements of the radiation from the source or of its coupling to external
electromagnetic waves. In other words, there is no toroidal radiation or
independent toroidal electromagnetic coupling. The formal meaning of the
toroidal multipoles is clear in our derivations. They are the higher order
terms of an expansion of the multipolar coefficients of electric parity with
respect to the electromagnetic size of the source
Objects of maximum electromagnetic chirality
We introduce a definition of the electromagnetic chirality of an object and
show that it has an upper bound. Reciprocal objects attain the upper bound if
and only if they are transparent for all the fields of one polarization
handedness (helicity). Additionally, electromagnetic duality symmetry, i.e.,
helicity preservation upon interaction, turns out to be a necessary condition
for reciprocal objects to attain the upper bound. We use these results to
provide requirements for the design of such extremal objects. The requirements
can be formulated as constraints on the polarizability tensors for dipolar
objects or on the material constitutive relations for continuous media. We also
outline two applications for objects of maximum electromagnetic chirality: a
twofold resonantly enhanced and background-free circular dichroism measurement
setup, and angle-independent helicity filtering glasses. Finally, we use the
theoretically obtained requirements to guide the design of a specific
structure, which we then analyze numerically and discuss its performance with
respect to maximal electromagnetic chirality.Comment: This version contains an example of how to use the theoretically
derived constraints for designing realistic structures. It also contains a
discussion related to the optical chirality densit
Dual and chiral objects for optical activity in general scattering directions
Optically active artificial structures have attracted tremendous research
attention. Such structures must meet two requirements: Lack of spatial
inversion symmetries and, a condition usually not explicitly considered, the
structure shall preserve the helicity of light, which implies that there must
be a vanishing coupling between the states of opposite polarization handedness
among incident and scattered plane waves. Here, we put forward and demonstrate
that a unit cell made from chiraly arranged electromagnetically dual scatterers
serves exactly this purpose. We prove this by demonstrating optical activity of
such unit cell in general scattering directions.Comment: This document is the unedited Authors version of a Submitted Work
that was subsequently accepted for publication in ACS Photonics, copyright
American Chemical Society after peer review. To access the final edited and
published work see
http://pubs.acs.org/articlesonrequest/AOR-3yvzAibCIU6wdTuzx9c
The polychromatic T-matrix
The T-matrix is a powerful tool that provides the complete description of the linear interaction between the electromagnetic field and a given object. In here, we generalize the usual monochromatic formalism to the case of polychromatic field-matter interaction. The group of transformations of special relativity provides the guidance for building the new formalism, which is inherently polychromatic. The polychromatic T-matrix affords the direct treatment of the interaction of electromagnetic pulses with objects, even when the objects move at constant relativistic speeds
Multidimensional measures of electromagnetic chirality and their conformal invariance
Proper assignment of left- and right-handed labels to general chiral objects is known to be a theoretically unfeasible problem. Attempts to utilize a pseudoscalar function to distinguish enantiomers face two unavoidable difficulties: false chiral zeros and unhanded chiral states. In here, we demonstrate how both of these problems can be solved in the context of light-matter interactions. First, we introduce a two-dimensional quantity called complex electromagnetic chirality that solves the problem of false chiral zeros. Next, we define an infinite-dimensional pseudovector called chirality signature that completely quantifies the multidimentional nature of electromagnetic chirality, does not have false global chiral zeros, and allows to continuously distinguish any pair of enantiomers. We prove that the introduced measures are invariant under the largest group of symmetries of Maxwell’s equations – the conformal group. The complete and conformally invariant quantification of electromagnetic chirality provided by the chirality signature distinguishes it as a particularly suitable tool for the study of chirality and its applications
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