The influence of UV irradiation on magneto-optical effects in AZO-derivative doped liquid crystals

Azo-derivative doped nematic liquid crystals were subjected to different d.c. magnetic fields and optical transmissions of a He-Ne laser beam (632.8 nm, 1 mW) were recorded for different field strengths. In order to follow these effects both Faraday and Voigt configurations were used, i.e. the magnetic field was parallel and perpendicular to the incident light, respectively. It was found that small addition of azo-dyes (2% by weight) induced optical activity into the nematic liquid crystal cells. The rotation angle and the light transmission varied periodically with the applied magnetic field. When subjecting the cells to UV irradiation, changes in the periodical behaviour of light transmission and optical activity were noticed. The cells behave like phase retardation plates, the phase difference depending on cell thickness, magnetic field strength and UV irradiation time.