Experimental and theoretical investigation of the co-occurrence of linear and circular dichroisms for oblique incidence of light on chiral sculptured thin films

TL;DR

This paper combines theoretical analysis and experimental validation to explore how oblique light incidence on chiral thin films induces both linear and circular dichroisms, revealing the influence of structural handedness and propagation direction.

Contribution

It provides a comprehensive investigation of linear and circular dichroisms in chiral thin films, including experimental spectra and the effects of handedness and light propagation direction.

Findings

Circular dichroism sign reverses with handedness change.

Signatures of the circular Bragg phenomenon are observed in spectra.

Linear dichroism remains unaffected by handedness reversal.

Abstract

Theory shows that a slab of a dielectric structurally chiral material (DSCM) exhibits both linear and circular dichroisms because of its anisotropy and structural chirality, for normal as well as oblique incidence. This conclusion was confirmed by fabricating a chiral sculptured thin film and measuring the spectra of its reflectances and transmittances, both linear and circular. Signatures of the circular Bragg phenomenon are evident in the spectra of all reflectances, transmittances, absorptances, and dichroisms. Reversal of the structural handedness of a DSCM and rotation of the projection of the direction of propagation of the incident light clockwise instead of counterclockwise about the axis of helicoidal nonhomogeneity simultaneously changes the sign of circular dichroism but has no effect on linear dichroism.