Electromechanical effects in free standing FLC elastomer films as determined by interferometric measurements

The electrically induced thickness variations of homeotropically oriented f ree standing films of a smectic (C* and A*) ferroelectric liquid crystallin e elastomer (FLCE) have been examined. For this purpose an interferometric setup has been built with a resolution of 3 pm at 133 Hz AC excitation freq uency. The laser beam has been focussed by means of two "long distance" mic roscope objective lenses in order to study small homogeneous areas in the f ilm. The changes in optical pathlength through the sample were measured at the first (omega), second (2 omega) and fourth (4 omega) harmonic of the AC -electric excitation voltage (omega = 133 Hz). The measured thickness (opti cal pathlength) modulation at the 2(nd) harmonic is in the range of some % and thus stronger than expected from FTIR-measurements on the electroclinic effect in CaF2 cells filled with this sample. Nevertheless, the strength o f this quadratic effect and also of the linear effect is greatly increased at the phase transition Sm-C*-Sm-A*, which indicates a correlation of the t hickness variation with the electroclinic effect.