Electrooptic measurement in the vicinity of SmA-SmC alpha* phase transition of an antiferroelectric liquid crystal

EIectrooptic measurements have been performed around the SmA-SmCalpha+ phas e transition point in an antiferroelectric liquid crystal 4-(1-methyl-hepty loxycarbonyl)phenyl 4' -octyloxybiphenyl-4-carboxylate (MHPOBC). The first- order electrooptic response was continuous with a small slope change at the SmA to SmCalpha* transition point in the temperature dependence curve, whi le the second-order electrooptic response exhibited an anomalous increase n ear the transition point. We present a simple theory and demonstrate that t his anomaly originates in the pretransitional fluctuations. The frequency d ispersion of the electrooptic response is also presented.