  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.
