Electro-optic response of an antiferroelectric liquid crystal in submicroncells

The dynamics of chiral smectic phases of antiferroelectric liquid crystal M HPOBC in a confined geometry has been analysed. Using an electro-optic resp onse technique, the temperature dependences of the relaxation rates and ele ctro-optic strengths of the elementary excitations in thin. planar aligned, wedge-type cells of thickness from 0.3 to 4 mum have been measured and com pared with those for a 50 mum hometropically aligned cell. The effects of t he confined geometry are the following. (i) The smectic C-gamma* phase does not exist in planar aligned cells with thickness less than 4 mum. Instead of this phase, we have observed the coexistence of the ferroelectric smecti c C* phase and the antiferroelectric smectic C-A* phase over a very wide te mperature range. (ii) The smectic C-alpha* phase is stable at all measured thicknesses down to 0.3 mum. (iii) We have observed a decrease of the smect ic A-smectic C-alpha* phase transition temperature, proportional to the inv erse of the cell thickness. (iv) Additional. thickness-independent phase mo des have been observed above some critical value of the measuring electric field in all tilted phases.