Achieving long-wavelength infrared (LWIR) cameras with high sensitivity and shorter exposure times faces challenges due to series reflections from high-refractive index lenses within compact optical systems. However, designing effective antireflective coatings to maximize light throughput in these systems is complicated by the limited range of transparent materials available for the LWIR. This scarcity narrows the degrees of freedom in design, complicating the optimization process for a system that aims to minimize the number of physical layers and address the inherent large refractive mismatch from high-index lenses. In this study, we use discrete-to-continuous optimization to design a subwavelength-thick antireflective multilayer coating on high-refractive index Si substrate for LWIR cameras, where the coating consists of few (e.g., five) alternating stacks of high- and low-refractive-index thin films (e.g., Ge-YF3, Ge-ZnS, or ZnS-YF3). Discrete optimization efficiently reveals the configuration of physical layers through binary optimization supported by a machine learning model. Continuous optimization identifies the optimal thickness of each coating layer using the conventional gradient method. As a result, considering the responsivity of a LWIR camera, the discrete-to-continuous strategy finds the optimal design of a 2.3-μm-thick antireflective coating on Si substrate consisting of five physical layers based on the Ge-YF3 high-low index pair, showing an average reflectance of 0.54 % within the wavelength range of 8–13 μm. Moreover, conventional thin-film deposition (e.g., electron-beam evaporator) techniques successfully realize the designed structure, and Fourier-transform infrared spectroscopy (FTIR) and thermography confirm the high performance of the antireflective function.

中文翻译：

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用于长波长红外相机的高折射率基底上反射率达 0.5% 的超薄 Ge-YF3 抗反射涂层


由于紧凑光学系统中高折射率镜头的串联反射，实现高灵敏度和更短曝光时间的长波长红外 (LWIR) 相机面临着挑战。然而，由于可用于长波红外的透明材料范围有限，设计有效的抗反射涂层以最大限度地提高这些系统中的光通量变得复杂。这种稀缺性缩小了设计的自由度，使系统的优化过程变得复杂，该系统旨在最大限度地减少物理层的数量并解决高折射率镜片固有的大折射失配问题。在这项研究中，我们使用离散到连续的优化来设计用于长波红外相机的高折射率硅基板上的亚波长厚的抗反射多层涂层，其中涂层由少量（例如五个）交替的高低折射率堆叠组成。 -折射率薄膜（例如Ge-YF3、Ge-ZnS或ZnS-YF3）。离散优化通过机器学习模型支持的二进制优化有效地揭示了物理层的配置。持续优化使用传统的梯度方法确定每个涂层的最佳厚度。因此，考虑到长波红外相机的响应度，离散到连续策略找到了基于 Ge-YF3 高低折射率的 2.3 μm 厚的硅衬底抗反射涂层的最佳设计，该涂层由五个物理层组成对，在 8–13 μm 波长范围内的平均反射率为 0.54%。此外，传统的薄膜沉积（例如、电子束蒸发器）技术成功实现了设计的结构，傅里叶变换红外光谱（FTIR）和热成像证实了抗反射功能的高性能。