PHOTOFLEXOELECTRIC EFFECTS IN A HOMEOTROPIC GUEST-HOST NEMATIC

The photoflexoelectric effect in homeotropic MBBA/D1 azo-dye nematic l ayers in a horizontal electric field subjected to UV illumination was investigated. About 10 per cent, reversible increase of the flexorespo nse (i.e. the increment of transmitted light intensity between crossed polarisers due to an in-plane electric field) was found under epi-UV- illumination, with relaxation times of the order of 15 s. The d.c. vol tage dependences of both dark and light flexoresponses followed the pr edictions of the theory. An UV-dependent amplification of the amplitud e of flexo-oscillations (excited by an a.c. voltage) was also register ed. The relative importance of bulk and surface contributions to the p hotoflexoresponse was discussed.