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Tailoring optical and radiative properties has attracted significant attention recently due to its importance in advanced energy systems, nanophotonics, electro-optics, and nanomanufacturing. Metamaterials with micro- and nanostructures exhibit exotic radiative properties with tunability across the spectrum, direction, and polarization. Structures made from anisotropic or nanostructured materials have shown polarization-selective absorption bands in the mid-infrared. Characterizing the optical and radiative properties of such materials is crucial for both fundamental research and the development of practical applications. Mueller matrix ellipsometry offers a nondestructive and noninvasive technique for characterizing radiative properties. Although such ellipsometers have long been used to measure optical properties, their operational bandwidth is usually limited to the visible to near-infrared range, leaving the mid-infrared largely unexplored. In this work, a broadband mid-infrared ellipsometer, operating from 2 to 15 μm, is designed and constructed to measure 12 elements of the Mueller matrix. The results may be used to determine the full Mueller matrix under specific conditions. The performance of the ellipsometer is evaluated using nanostructured materials, including a 1D grating and a chiral F-shaped metasurface. The measurement results compared well to those obtained from rigorous-coupled-wave analysis and finite-difference time-domain simulations, suggesting that this setup offers a useful tool in optical property retrieval and the assessment of nanostructured materials. 

Abstract Polarized thermal emission finds extensive applications in remote sensing, landmine detection, and target detection. In applications such as ellipsometry and biomedical analysis, the generation of emission with controllable polarization is preferred. It is desired to manipulate the polarization state over the full Stokes parameters. While numerous studies have demonstrated either linear or circular polarization control using metamaterials, full-Stokes thermal emission has not been explored. Here, a microstructure based on two layers of silicon carbide gratings is proposed to tailor the polarization state of thermal emission, covering the full-Stokes parameter range. The bilayer twisted-gratings structure breaks mirror symmetry. Wave interference at the interfaces and diffraction by the gratings enhance the emission dichroism, resulting in almost completely polarized emission. By adjusting the twist angle between the gratings, the polarization state can be continuously tuned from linear to circular, nearly covering the entire surface of Poincaré sphere. This study provides a design for tailoring full-Stokes emission with notable advantages over other plasmonic metasurfaces. 

The British landscape painter John Constable is considered foundational for the Realist movement in 19th-century European painting. Constable’s painted skies, in particular, were seen as remarkably accurate by his contemporaries, an impression shared by many viewers today. Yet, assessing the accuracy of realist paintings like Constable’s is subjective or intuitive, even for professional art historians, making it difficult to say with certainty what set Constable’s skies apart from those of his contemporaries. Our goal is to contribute to a more objective understanding of Constable’s realism. We propose a new machine-learning-based paradigm for studying pictorial realism in an explainable way. Our framework assesses realism by measuring the similarity between clouds painted by artists noted for their skies, like Constable, and photographs of clouds. The experimental results of cloud classification show that Constable approximates more consistently than his contemporaries the formal features of actual clouds in his paintings. The study, as a novel interdisciplinary approach that combines computer vision and machine learning, meteorology, and art history, is a springboard for broader and deeper analyses of pictorial realism. 

We numerically investigated the possibility to obtain circularly polarized infrared thermal emission from a bilayer scheme taking advantage of the strong anisotropy of low symmetry materials such as -Ga2O3 and -MoO3. Our results show that it is possible to achieve a high degree of circular polarization over 0.85 at two typical emission frequencies related to the excitation of -Ga2O3 optical phonons. Our simple but effective scheme could set the basis for a new class of lithography-free thermal sources for IR bio-sensing. 

The focus of this work is on the measurement and analysis of the radiative properties of polycrystalline SiO2 particle beds with various layer thicknesses. The particles are polydispersed with average diameters of 222, 150, and 40 μm. The spectral, directional–hemispherical reflectance and transmittance of the particle bed are measured at wavelengths from 0.4 to 1.8 μmusing a monochromator, and the reflectance measurement is extended to 15 μmusing a Fourier-transform infrared spectrometer. Particles are closely packed between two transparent windows for measuring the radiative properties. In the visible and near-infrared region up to 1.8 μm, the inverse adding–doubling method yields the effective absorption and scattering coefficients. The results suggest that short wavelength absorption needs to be included in modeling the behavior of particle beds due to multiple scattering. A discrete-scale Monte Carlo ray-tracing method is developed to model the radiative properties by assuming monodispersed spherical particles, and the simulated results compare well with measurements. The effective absorption and scattering coefficients of the particle beds obtained from the independent scattering theory are compared to those from the inverse method. The impact of dependent scattering on the packed beds is observed for smaller-sized particles.