Molecular motion in a smectic liquid crystal showing V-shaped switching asstudied by optical second-harmonic generation

The molecular motion during the V-shaped switching in a homogeneously align ed smectic-C*-like liquid crystal (LC) cell has been investigated by means of second-harmonic generation (SHG) and SHG interferometry. At normal incid ence, SHG intensity profiles were observed as a function of applied electri c field for four combinations of input-output polarizations of light. For t he analysis of SHG results, the V-shaped switching system was considered as a ferroelectric uniform state with C-2 symmetry (collective model). It was shown that the observed SHG behavior was successfully simulated using the collective model. By using SHG interferometry measurements, it was found th at azimuthal rotation of LC molecules is limited within half the cone, wher e molecules could distribute. Moreover, it was also found that LC molecules undergo counterazimuthal rotation in the upper and lower halves of the LC layer in chevron structure. The stabilization of the uniform molecular alig nment was attributed to the escape from the formation of polarization charg es and a surface molecular constraint. The mechanism of the collective moti on was discussed on the basis of the softening of the system due to the fru stration of ferroelectric and antiferroelectric interactions.