Investigations of nanoscale helical pitch in smectic- Cα* and smectic- C* phases of a chiral smectic liquid crystal using differential optical reflectivity measurements

Differential optical reflectivity (DOR) was used to study the temperature dependence of the short helical pitch in freestanding films of a liquid crystal compound. The experimentally measured DOR signal was fitted using Berreman’s 4-4 matrix method to get the pitch value in the smectic- Cα* (Sm Cα*) phase. The results show continuous evolution of the pitch between the smectic- C* and Sm Cα* phases. In Sm Cα*, the pitch decreases as temperature increases and is found to level off at 16±1 smectic layers at the Sm Cα* to smectic- A* transition.