Critical behavior of birefringence in the smectic-<i>A</i>phase of chiral smectic liquid crystals

Abstract

Using a high resolution polarimeter, we have measured the temperature dependence of birefringence in the vicinity of smectic-A--smectic-${C}^{*},$ smectic-A--smectic-${C}_{\ensuremath{\alpha}}^{*},$ and smectic-A--smectic-${C}_{A}^{*}$ phase transitions of chiral smectics. We have observed a large pretransitional decrease of the birefringence in materials exhibiting smectic-${C}_{\ensuremath{\alpha}}^{*}$ and smectic-${C}_{A}^{*}$ phases, indicating unusually large pretransitional fluctuations of the tilt angle. These fluctuations show a clear power-law behavior over more than two decades of temperature.