双掺杂LiNbO_3:Fe:Mn晶体局域光折变体全息光栅形成及衍射特性

Formation and Diffraction Characteristics of Local Volume Photorefractive Holographic Gratings in Two Doped LiNbO_3:Fe:Mn Crystals

将带输运模型与二维耦合波理论相结合,研究了双掺杂LiNbO3∶Fe∶Mn晶体中由两束有限宽度平面波干涉产生的局域光折变体全息的动力学机制及其衍射特性。采用三步法联立求解了双中心带输运物质波方程和二维耦合波方程。数值计算结果表明,局域光折变体全息光栅的空间电荷场在空间上呈不均匀分布。当光栅区域较小时空间电荷场较强,随着光栅区域的增大,空间电荷场急剧下降,并降低一个数量级。此外,在接近光束入射边界的区域,空间电荷场时空变化规律与一维无限大光折变体全息光栅的结果相似,随着光栅区域的扩大,边界效应对空间电荷场的影响越显著。研究还发现,局域光折变体全息光栅的衍射效率随光栅厚度的增加而增加。理论结果对于由局域光折变体全息光栅形成的光学器件与系统的设计和应用具有重要的参考意义。

Both dynamic mechanisms and diffraction characteristics of the local volume photorefractive holographic gratings recorded by two finite bounded plane waves in doubly doped LiNbO3 ： Fe： Mn crystals are investigated, by taking into account both the band transport model and two-dimensional coupled-wave theory. The three step method is used to solve both the band transport equation and the two-dimensional coupling equation. The numerical calculations show that the spatial distribution of the space-charge field is non homogeneous in the local volume photorefractive holographic gratings. The space-charge field is much stronger when the grating region is smaller. As the grating region widening, the space-charge field decreases by an order of magnitude. Besides, the time-space variation of the space-charge field is the same as that of one dimension infinite photorefractive holographic gratings in the place closer to the incident boundary. But the influence of the special local effect on the space-charge field is very important as the grating region extends. It is also shown that the diffraction efficiency increases with the increase of the grating length of the local volume photorefractive holographic gratings. The theoretical results provide valuable insight to the design and application of these gratings and the finite boundary photorefractive holographic optical elements.