Photorefractive gratings in C₆₀-doped nematic liquid crystals under non-biased sinusoidal alternating electric fields

Abstract

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 C₆₀-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.

Keywords:

• diffraction gratings
• nematic liquid crystals
• photorefractive effect
• space-charge field

Acknowledgements

This research was supported by the National Natural Science Foundation of China under Grant No. 60808027 and China Postdoctoral Science Foundation (20080440894), Heilongjiang Postdoctoral Financial Assistance under Grant No. LBH-Z08106, and Natural Science Foundation of Heilongjiang Province of China under Grant No. A200915.