Dispersion of the Sm-C/emph>order-parameter fluctuations in the Sm-Aand Sm-C/emph>phases of 4-(2’-methylbutyl) phenyl 4’-n-octylbiphenyl-4-carboxylate

The temperature dependence and dispersion relation of phason and amplitudon relaxation times were measured in Sm-A and Sm-$C^{\mathrm{*}}$ phases of the ferroelectric liquid crystal S-(+)-[4-(2’-methylbutyl) phenyl 4’-n-octylbiphenyl-4-carboxylate] (CE8) by photon correlation spectroscopy. In the Sm-A phase both modes are degenerate, their inverse relaxation time is strongly temperature dependent and has a parabolic dispersion relation with a minimum at a finite wave vector. In the Sm-$C^{\mathrm{*}}$ phase, the amplitudon relaxation time is temperature dependent, while the phason relaxation time is temperature independent and shows parabolic dispersion. The ratios of two orientational elastic constants and the viscosity were obtained at different temperatures. In addition, the temperature dependence of the helical pitch has been measured in the Sm-$C^{\mathrm{*}}$ phase of CE8 in homeotropic and bookshelf-geometry alignments.