Optical fully leaky mode characterization of a standard liquid-crystal cell

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Abstract
Optical excitation of fully leaky guided modes is used to characterize in detail the optical tensor profile in a liquid-crystal layer confined between two standard glass plates as for a conventional cell. The angle-dependent reflectivity and transmissivity of such a structure are explored analytically, numerically, and experimentally. By suitable choice of incident and detected polarizations it is shown possible to obtain a detailed characterization of the director profile in the cell even though the leaky optical modes lead to rather broad features in the recorded data. Using a two-prism coupling technique, matching the prisms to the glass of the cell with identical index-matching fluid, allows access to sets of both reflectivity data and transmissivity data over a sufficient range of in-plane photon wave vectors to yield unambiguous director profiles when the data are compared with modeling theory. The specific cell explored in this study contains a homogeneously aligned ferroelectric smectic material in which there is a cusped, chevron, director profile. The results presented for such a complex structure show that this powerful new form of quantified conoscopy is likely to provide the primary route forward for optical characterization of conventional cells of this nature.