The dielectric response of surface stabilized ferroelectric liquid crystalswith chevron layer structure is studied within low and intermediate frequencyranges, characteristic for collective molecular excitations. By analyticallysolving the dynamic equation for collective molecular fluctuations under a weakalternating electric field, it is demonstrated that chevron cells stabilized byboth nonpolar and polar surface interactions undergo at medium frequencies twoDebye relaxation processes, connected with two chevron slabs, on opposite sidesof the interface plane. This result is confirmed, experimentally, making use ofthe electro-optic technique. Based on qualitative arguments supported bymicroscopic observations of zigzag defects at different frequencies andamplitudes of the external electric field, it is shown that, at lowfrequencies, the electro-optic response of chevron samples is determined bythree kinds of motions of zigzag walls. The first two dynamic categories arerelated to collective relaxation processes at weak fields, within smectic Alayers forming zigzag walls, and drift or creep motions of thick walls occuringat stronger field amplitudes. Dynamic processes of the third kind correspond tosliding of zigzag walls, which appear at yet stronger field amplitudes, butbelow the switching threshold.
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