Abstract
Optical chirality, in terms of circular birefringence and circular dichroism, is described by its electromagnetic and magnetoelectric material tensors, and the corresponding optical activity contributes to the Mueller matrix. Here, spectroscopic ellipsometry in the spectral range 210–1690 nm is used to address chiral phenomena by measuring Mueller matrices in transmission. Three approaches to determine chirality parameters are discussed. In the first approach, applicable in the absence of linear polarization effects, circular birefringence and circular dichroism are evaluated directly from elements of a Mueller matrix. In the second method, differential decomposition is employed, which allows for the unique separation of chirality parameters from linear anisotropic parameters as well as from depolarization provided that the sample is homogeneous along the optical path. Finally, electromagnetic modeling using the Tellegen constitutive relations is presented. The last method also allows structural effects to be included. The three methods to quantify optical chirality are demonstrated for selected materials, including sugar solutions, α-quartz, liquid crystals, beetle cuticle, and films of cellulose nanocrystals.
Highlights
Mueller matrices are increasingly used for the analysis of bianisotropic properties of complex media, including the quantification of circular birefringence (CB) and circular dichroism (CD)
Chiral parameters are studied by CD-spectroscopy and optical rotatory dispersion (ORD) methods
II In method II, we apply a differential decomposition to the data in Figure 1 with the results presented in Figure 2, which confirms that the linear effects linear birefringence (LB), linear dichroism (LD), LB, and LD are very small
Summary
Mueller matrices are increasingly used for the analysis of bianisotropic properties of complex media, including the quantification of circular birefringence (CB) and circular dichroism (CD). The purpose here is to discuss how Mueller-matrix analysis can complement the established methods by providing additional analytic features. Of special significance is that access to a full Muller matrix allows for the separation of circularly polarizing effects from linear birefringence (LB) and linear dichroism (LD). Both CB and CD are accessible simultaneously from a Mueller matrix providing consistency checks through Kramers–Kronig analysis. If a sample is depolarizing, the differential decomposition of a Mueller matrix can be employed to separate out depolarization so that it will not distort the analysis of chirality or linearly polarizing effects. To facilitate a comparison among different approaches, the use of transmission Mueller matrices to determine the chirality in samples is briefly reviewed and examples of data analysis from liquid and solid homogeneous as well as structured samples are discussed
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