Photorefractive gratings in C_(60)-doped nematic liquid crystals under non-biased sinusoidal alternating electric fields

摘要

We report on the effect of the frequency of a non-biased sinusoidal alternating (AC) electric field on the optical non-linear response of 60 μm-thick homeotropic C_(60)-doped nematic liquid crystals by using a two-beam coupling experiment. Experimental results indicate that the liquid crystal sample has two intrinsic frequencies of ~0.05 Hz and ~10 Hz. Below 0.05 Hz the energy transference is unstable, the first-order diffraction flashes in phase with the external AC electric field and its minimal intensity is almost zero. When the frequency is larger than ~10 Hz, stable asymmetric energy transference, as that achieved under an external DC electric field, is obtained. In the regions between the above two frequencies, a stable asymmetric energy transference exists; at the same time, the transmitted intensities of the two writing beams are modulated by the external AC field and follow its variations.