On the Possibility of Improving the Average Chirality and Dissymmetry Factor Using Periodic Structures

Chirality is an important property of molecules. Although its sensing is crucial in chemical processes, the sensitivity of the measurement is limited. By increasing the optical chirality (OC) or, more precisely, increasing the dissymmetry factor g of the impinging electromagnetic fields, this sensitivity can be enhanced. All the chirality enhancement techniques introduced so far, increase the OC locally. It is a question whether it is possible to design a structure to enhance the average OC on a certain cross section, such that, the average of the dissymmetry factor g is increased too. This paper analytically answers this question about periodic structures. Our analytical results reveal that this goal is inaccessible. The reported results are evaluated and confirmed by simulations. Finally, we show that increasing average of the dissymmetry factor g in the free-space is also impossible. In fact, we prove that a collection of plane waves propagating in the positive z-direction, cannot boost the average of the dissymmetry factor g in the xy plane.