Experimental study of the dynamic behaviour of twisted ferroelectric liquid crystal samples using snap-shot Mueller matrix polarimetry
Résumé
The full-optical set-up snap-shot Mueller matrix polarimeter (SMMP) is used to measure the channelled spectrum Iλ(λ) related to a twisted ferroelectric liquid crystal (TwFLC) studied here with this technique. The samples were preliminarily exposed to a high-amplitude/low-frequency rectangular voltage before all the optical measurements. This voltage applied permits one to work in the specific stripe regime. From the channelled spectrum recorded Iλ(λ), the different Mueller matrix (MM) can be obtained: the depolarization matrix, the retardance matrix and the diattenuation matrix. Several scalar polarimetric parameters are extracted from these MM, and especially αR(t), R(t) and R(t). These relevant scalar coefficients, calculated from the retardance matrix, are used to determine the three hysteresis loops αR(V), R(V) and R(V). We define ψ as the difference of angle between the two rubbing directions of the two symmetrical (top and bottom) substrates and we examine how the hysteresis loops obtained are modified with the value of the geometrical externally controllable parameter ψ, for angles between ψ = 0° and ψ = 90°. The key characteristics of the hysteresis loops and the evolution of these key values with ψ are detailed.