平均结构参数变化的光栅中的极不对称散射
Extremely asymmetrical scattering in gratings with varying mean structural parameters
摘要：
极不对称散射（EAS）是倾斜周期光栅中的一种特殊类型的布拉格散射，其散射波（+1衍射级）平行于光栅边界传播。在这里，一个独特的和强大的灵敏度EAS的光栅边界处的平均结构参数的小的逐步变化的理论预测（通过近似和严格的分析）为体TE电磁波和平板光学模式的任意偏振的全息（体波）和光栅（平板模式）。预测的效果解释使用EAS的主要物理原因之一-散射波的衍射发散（类似于激光束的发散）。分析的近似方法是基于这种理解的散射波的发散的作用，而严格的分析使用增强的T矩阵算法。分析了在光栅边界处平均介电常数的小的和大的逐步变化的影响。两个明显不同的和不寻常的模式EAS预测的情况下，宽和窄（相比的临界宽度）光栅。近似理论和严格理论之间的比较进行。
英文摘要：
Extremely asymmetrical scattering (EAS) is an unusual type of Bragg scattering in slanted periodic gratings with the scattered wave (the +1 diffracted order) propagating parallel to the grating boundaries. Here, a unique and strong sensitivity of EAS to small stepwise variations of mean structural parameters at the grating boundaries is predicted theoretically (by means of approximate and rigorous analyses) for bulk TE electromagnetic waves and slab optical modes of arbitrary polarization in holographic (for bulk waves) and corrugation (for slab modes) gratings. The predicted effects are explained using one of the main physical reasons for EAS--the diffractional divergence of the scattered wave (similar to divergence of a laser beam). The approximate method of analysis is based on this understanding of the role of the divergence of the scattered wave, while the rigorous analysis uses the enhanced T-matrix algorithm. The effect of small and large stepwise variations of the mean permittivity at the grating boundaries is analysed. Two distinctly different and unusual patterns of EAS are predicted in the cases of wide and narrow (compared to a critical width) gratings. Comparison between the approximate and rigorous theories is carried out.
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