CIRCULAR-DICHROISM IN FERROELECTRIC AND ANTIFERROELECTRIC LIQUID-CRYSTALS

Liquid crystal induced circular dichroism (LCICD) measurements were made to investigate the pretransitional phenomena in the S-A phase just above the S-A-S-C* and S-A-S-CA* phase transitions of both the first and the second order. The pretransitional LCICD in S-A was observed in the second order phase transition to S-C* and S-CA*, suggesting the existence of a dynamic helical structure in S-A. Such behaviour disappears when the transition is of the first order. It seems that the handedness of the dynamic helix in S-A is the same as that in S-C* even when the lower temperature phase is S-CA*. This is explained as a result of a dominant contribution of ferroelectric soft mode.