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Broadband Omnidirectional Diffuse Mirrors with Hierarchically Designed All-Dielectric Surfaces
ACS Photonics ( IF 7 ) Pub Date : 2018-01-03 00:00:00 , DOI: 10.1021/acsphotonics.7b01364
Yoon-Jong Moon 1 , Jin-Young Na 1 , Yong Hyun Park 2 , Soo Bin Kim 2 , Sang Woon Lee 2 , Sun-Kyung Kim 1
Affiliation  

An electromagnetic wave with a single wave vector can be converted into multiple partial ones, with discrete or continuum wave vectors, by means of diffraction or scattering elements; this phenomenon is called optical diffusion. Optical diffusion is a crucial light–matter interaction problem, particularly for lighting applications that require uniform illumination. However, omnidirectional diffuse mirrors with minimal absorption loss have not been reported thus far. Here, we demonstrate the high-diffusivity, low-absorption reflecting surfaces, on which hexagonally arranged Al2O3 cones, with a pitch of 3 μm, are conformally covered with HfO2/Al2O3 multilayers. Spectrally resolved far-field measurements reveal that the hierarchically patterned surface diffuses reflected light uniformly over the entire range of azimuthal and polar angles at broadband wavelengths (λ = 400–800 nm), distinct to two-dimensional Al2O3 or Al patterned surfaces. Such omnidirectional optical diffusion is clearly identified by means of the momentum space representation; the hierarchical pattern allows all of the available diffraction modes to possess nearly equal amplitudes, which is strongly supported by near-to-far-field Fourier analysis. The degree of diffusivity is quantitatively evaluated with respect to different angular ranges (Δθ = 3°, 12°, and 24°) around a specular reflection angle. Under all of the considered metrics, the hierarchical pattern yields a relatively large diffusivity compared to the reference two-dimensional patterns. Measurements of reflectance spectra, together with full-vectorial electromagnetic simulations, suggest that the hierarchically patterned surface with a backside reflector serves as a high-reflectance diffuse mirror, contrasting with a patterned Al mirror that inevitably suffers from plasmonic absorption loss. These experimental and numerical findings studied herein will provide a fundamental platform for achieving omnidirectional optical diffusers.

中文翻译:

具有分层设计的全介电表面的宽带全向漫反射镜

具有单个波矢的电磁波可以通过衍射或散射元素转换为具有离散或连续波矢的多个部分波;这种现象称为光扩散。光学扩散是一个至关重要的光-物质相互作用问题,尤其是对于需要均匀照明的照明应用而言。然而,迄今为止,尚未报道具有最小吸收损耗的全向漫反射镜。在此,我们演示了高扩散率,低吸收率的反射表面,在该表面上六边形排列的Al 2 O 3锥体(间距为3μm)被HfO 2 / Al 2 O 3保形覆盖。多层。光谱分辨的远场测量表明,分层图案化的表面在宽带波长(λ= 400–800 nm)上与二维Al 2 O 3不同,在整个方位角和极角范围内均匀地反射了反射光或Al图案的表面。通过动量空间表示法可以清楚地识别出这种全方位的光扩散。分级模式允许所有可用的衍射模式具有几乎相等的振幅,这由近场傅里叶分析强烈支持。对于围绕镜面反射角的不同角度范围(Δθ= 3°,12°和24°),定量评估扩散程度。在所有考虑的度量标准下,与参考二维模式相比,分层模式会产生相对较大的扩散率。反射光谱的测量以及全矢量电磁模拟表明,带有背面反射器的分层图案化表面可以用作高反射漫反射镜,与图案化的铝镜形成对比,铝镜不可避免地遭受等离子体吸收损失。本文研究的这些实验和数值发现将为实现全向光学漫射器提供基础平台。
更新日期:2018-01-03
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