Photoflexoelectric effects in a homeotropic guest-host nematic

The photoflexoelectric effect in homeotropic MBBA/D1 azo-dye nematic layers in a horizontal electric field subjected to UV illumination was investigated. About 10 per cent, reversible increase of the flexoresponse (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. voltage dependences of both dark and light flexoresponses followed the predictions of the theory. An UV-dependent amplification of the amplitude of flexo-oscillations (excited by an a.c. voltage) was also registered. The relative importance of bulk and surface contributions to the photoflexoresponse was discussed.