Broadband Omnidirectional Diffuse Mirrors with Hierarchically Designed All-Dielectric Surfaces

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 ...