  Designing objects with predefined optical properties is a task of fundamental
importance for nanophotonics, and chirality is a prototypical example of such a
property, with applications ranging from photochemistry to nonlinear photonics.
A measure of electromagnetic chirality with a well-defined upper bound has
recently been proposed. Here, we optimize the shape of silver helices at
discrete frequencies ranging from the far infrared to the optical band.
Gaussian process optimization, taking into account also shape derivative
information of the helices scattering response, is used to maximize the
electromagnetic chirality. We show that the theoretical designs achieve more
than 90 percent of the upper bound of em-chirality for wavelenghts
\SI{3}{\micro\meter} or larger, while their performance decreases towards the
optical band. We fabricate and characterize helices for operation at
\SI{800}{\nano\meter}, and identify some of the imperfections that affect the
performance. Our work motivates further research both on the theoretical and
fabrication sides to unlock potential applications of objects with large
electromagnetic chirality at optical frequencies, such as helicity filtering
glasses. We show that, at \SI{3}{\micro\meter}, a thin slab of randomly
oriented helices can absorb 99 percent of the light of one helicity while
absorbing only 9 percent of the opposite helicity.
