向列相液晶中非对称相位光栅的产生及形貌  

Generation and profile of asymmetric dynamic phase grating in nematic liquid crystal

作　　者：任常愚 李尤 丁红伟 REN Changyu;LI You;DING Hongwei(Fuzhou College of Foreign Studies and Trade,Fuzhou 350202,China;School of Science,Heilongjiang University of Science and Technology,Harbin 150022,China)

机构地区：[1]福州外语外贸学院,福建福州350202 [2]黑龙江科技大学理学院,黑龙江哈尔滨150001

出　　处：《液晶与显示》2024年第9期1155-1162,共8页Chinese Journal of Liquid Crystals and Displays

基　　金：国家自然科学基金(No.12304280)。

摘　　要：为了研究液晶中相位光栅的动态衍射特性和光栅形貌,提出了在C_(60)掺杂垂直排列向列相液晶(NLC)中产生非对称光栅的方法,分析了光栅产生机制并建立了光栅形貌的数学模型。首先,用水平偏振光的斜入射光束写入相位光栅。然后,利用一束光作为探测光读出光栅并利用光电探测器记录衍射光强。实验表明,光栅的最大衍射效率超过60%,且衍射强度分布不对称。基于非对称衍射的特征,提出了基于光折变效应产生非对称衍射分布和衍射效率超过对称光栅Raman-Nath衍射理论极限的物理机制。最后,给出了在NLC中形成非对称锯齿形光栅的假设,并提出了描述非对称锯齿形相位光栅的数学模型。研究结果表明,相位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。这种非对称电场主要是表面电荷调制和Carr-Helfrich效应共同作用的结果。提出的非对称锯齿形光栅模型假设能够很好地描述非对称衍射和衍射效率突破Raman-Nath理论关于对称光栅衍射理论限制的原因。In order to study the dynamic diffraction characteristics and grating profile of phase gratings in liquid crystals(NLC),a new method used for recording the dynamic phase grating with an asymmetric profile in C_(60)doped homeotropically aligned nematic liquid crystal(NLC)is presented,the generation mechanism of grating is analyzed and the mathematical model of asymmetric profile is established.First,an oblique incidence parallel beams is used to record thin asymmetric dynamic phase holographic grating.Then,a beam of light is used as a probe to read out the grating and record the diffraction intensity with a photodetector.Experimental indicates that the maximum diffraction efficiency is more than 60%,and the diffraction intensity distribution is asymmetrical.Based on the characteristics of asymmetric diffraction distribution,the physical mechanism of producing asymmetric diffraction distribution and diffraction efficiency exceeding the theoretical limit of Raman-Nath diffraction of symmetric gratings is proposed based on photorefractive effect.Finally,the hypothesis of a grating with asymmetrical fringe close to saw-tooth profile formed in the NLC is given,and the mathematical model of describing asymmetric phase gratings is proposed.The results indicate that the high diffraction efficiency of the phase grating originates from the non-sinusoidal modulated space charge field in the liquid crystal.The asymmetric electric field is mainly the result of surface charge modulation and Carr-Helfrich effect.The proposed model of asymmetric saw-tooth profile grating can well describe the reason why the asymmetric diffraction and diffraction efficiency exceed the theoretical limit of symmetric profile gratings of Raman-Nath diffraction theory.

关 键 词：向列相液晶 非对称相位光栅 衍射效率 光折变效应 

分 类 号：O753.2[理学—晶体学]