Thickness-dependent spectral holes exhibited by a cascade of two slabs of dissimilar structurally chiral materials

A cascade of two slabs of dissimilar structurally chiral materials can function as a spectral hole filter for normally incident, circularly polarized light, provided (i) both have the same structural handedness and (ii) their constitutive parameters and thickness satisfy two matching conditions. When the total thickness of the cascade is relatively small, a narrow spectral hole is found in the reflection spectrum of co-handed light. Conversely, an ultranarrow spectral hole is found in the transmission spectrum of cross-handed light, when the total thickness of the cascade is relatively large.