  Electromagnetic waves impinging on three-dimensional helical metallic
metamaterials have been shown to exhibit chiral effects of large magnitude both
theoretically and in experimental realizations. Chirality here describes
different responses of scatterers, materials, or metamaterials to left and
right circularly polarized electromagnetic waves. These differences can be
quantified in terms of electromagnetic chirality measures. In this work we
consider the optimal design of thin metallic free-form nanowires that possess
measures of electromagnetic chirality as large as fundamentally possible. We
focus on optical frequencies and use a gradient based optimization scheme to
determine the optimal shape of highly chiral thin silver and gold nanowires.
The electromagnetic chirality measures of our optimized nanowires exceed that
of traditional metallic helices. Therefore, these should be well suited as
building blocks of novel metamaterials with an increased chiral response. We
discuss a series of numerical examples, and we evaluate the performance of
different optimized designs.
