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利用二波耦合(2BC)实验研究了掺杂C60垂直排列的向列相液晶(5CB)样品中形成光折变全息光栅的动态衍射特性。利用厚度为20μm的样品中记录的光折变全息光栅(光栅间距Λ≈24μm)获得了高达40%的一阶衍射效率,且衍射强度不对称分布。根据取向光折变效应体机制和表面电荷调制机制对此现象给出了解释,认为液晶中电场的增强是表面电荷调制和Carr-Helfrich效应共同作用的结果。薄光折变全息光栅的高衍射效率来源于液晶中非正弦调制的空间电荷场。数值模拟结果与实验测量结果一致,证实了所提出物理机制的正确性。
The dynamic diffraction characteristics of a photorefractive holographic gratings formed in a C60-aligned nematic liquid crystal (5CB) sample were studied by two-wave coupling (2BC) experiments. A first-order diffraction efficiency of up to 40% was obtained with a photorefractive holographic grating (grating pitch Λ ≈ 24 μm) recorded in a sample with a thickness of 20 μm, and the diffraction intensity was asymmetrically distributed. According to the orientation photorefractive effect mechanism and the surface charge modulation mechanism, this phenomenon is explained. The enhancement of the electric field in the liquid crystal is the result of the combination of the surface charge modulation and the Carr-Helfrich effect. The high diffraction efficiency of thin photorefractive holographic gratings derives from the non-sinusoidal modulated space charge field in liquid crystals. The numerical simulation results are in good agreement with the experimental measurements, confirming the correctness of the proposed physical mechanism.