On an objective experimental method for the determination of the electrohydrodynamic instability thresholds in a nematic liquid crystal

The case of an electrohydrodynamically excited and homogeneously aligned nematic liquid crystal layer, which exhibits a spatially periodic reorientation of its director field, is considered. A previously reported work proposed an optical method to measure the director relaxation time by diffraction, through monitoring the intensities of low-order fringes. This light diffraction technique was applied at a single frequency, while the excitation voltage was temporarily zero. The current article is a continuation of the aforementioned experimental technique. Here, we present a completely objective method for the experimental determination of the instability threshold at any given frequency in the conductive regime, based on the dependence of the decay time of the director field on the value of the AC voltage applied across the nematic layer when the excitation field is temporarily zero or lower than its corresponding threshold value.