Switching dynamics in homeotropic ferroelectric liquid crystals

The molecular motion during the switching in homeotropic cells of chiral-smectic-C materials has been investigated by means of second-harmonic generation and electrooptic measurements. The analysis of the results shows that the director reorientation takes place within microdomains of size smaller than the optical wavelength. There are two types of domains which occur with different probabilities, and in each of them the molecules rotate in opposite directions. Moreover the optical indicatrix rotates in a preferential direction, which indicates that the dipole moments move from 0 degrees to 360 degrees during a whole switching period. This contrasts with the back and forth rotation from 0 degrees to 180 degrees observed in planar cells. The results are analyzed in view of the macroscopic symmetry of a chiral-smectic-C phase and a simple qualitative model is proposed which explains the observed behavior.