Appl Opt. 2023 May 1;62(13):3398-3408. doi: 10.1364/AO.487810.
Suppressing Fresnel reflections from dielectric boundaries using periodic and random antireflection structured surfaces (ARSSs) has been vigorously studied as an alternative to thin film coatings for high-power laser applications. A starting point in the design of ARSS profiles is effective medium theory (EMT), approximating the ARSS layer with a thin film of a specific effective permittivity, which has features with subwavelength transverse-scale dimensions, independent of their relative mutual positions or distributions. Using rigorous coupled-wave analysis, we studied the effects of various pseudo-random deterministic transverse feature distributions of ARSS on diffractive surfaces, analyzing the combined performance of the quarter-wave height nanoscale features, superimposed on a binary 50% duty cycle grating. Various distribution designs were investigated at 633 nm wavelength for TE and TM polarization states at normal incidence, comparable to EMT fill fractions for a fused silica substrate in air. The results show differences in performance between ARSS transverse feature distributions, exhibiting better overall performance for subwavelength and near-wavelength scaled unit cell periodicities with short auto-correlation lengths, in comparison to equivalent effective permittivity designs that have less complicated profiles. We conclude that structured layers of quarter-wavelength depth and specific feature distributions can outperform conventional periodic subwavelength gratings as antireflection treatments on diffractive optical components.
使用周期性和随机抗反射结构表面（ARSS）抑制介电边界的菲涅尔反射，已作为用于高功率激光应用的薄膜涂层的替代方法得到了广泛研究。ARSS 轮廓设计的一个起点是有效媒质理论（EMT），该理论用特定有效介电常数的薄膜来近似 ARSS 层，其具有亚波长横向尺度的特征，与它们的相对相互位置或分布无关。我们使用严格的耦合波分析研究了 ARSS 的各种伪随机确定性横向特征分布对衍射表面的影响，分析了叠加在二进制 50%占空比光栅上的四分之一波长高度纳米特征的综合性能。在 633nm 波长下，针对 TE 和 TM 偏振状态进行了研究，与空气中熔石英基底的 EMT 填充率相当。结果表明，ARSS 横向特征分布之间的性能存在差异，与具有更简单轮廓的等效有效介电常数设计相比，具有较短自相关长度的亚波长和近波长比例单元周期性的整体性能更好。我们得出的结论是，与常规周期性亚波长光栅相比，深度为四分之一波长的特定特征分布的结构化层可以作为衍射光学元件的抗反射处理，从而具有更好的性能。
