Ultrasonic Wave Propagation in Twist-Structures of Liquid Crystal

Abstract
In twist structures of nematic liquid crystals (NLC) there are two special cases of elastic waves’ propagation. In first case, internal NLC structure does not influence on the ultrasonic wave propagation, and the acoustic velocity, in fact, coincides with the acoustic velocity of isotope phase. In second case, the «second» sound, for which velocity с_⊥ is defined by the wave vector q_o of the twist NLC structure, where с_⊥∼q_o, appears. As the curve parameters are changed in this situation, the NLC optical properties must be changed at ultrasonic wave propagation. The experimental method based on the modulation spectroscopy principles was suggested. It allows exact measuring of thin changes in optical spectra, that cannot be registered by usual optical spectrometers. The restored reflection spectrum allows getting information about the NLC spin influence on the ultrasonic wave propagation.

Keywords: nematic liquid crystal