Exploiting universal nonlocal dispersion in optically active materials for spectro-polarimetric computational imaging

Wang et al. eLight (2024) 4:22 https://doi.org/10.1186/s43593-024-00078-2 RESEARCH ARTICLE Exploiting universal nonlocal dispersion in optically active materials for spectro‑polarimetric computational imaging Xueji Wang1, Todd Van Mechelen1, Sathwik Bharadwaj1, Md Roknuzzaman2, Fanglin Bao1, Rajib Rahman2 and Zubin Jacob1*  Abstract  Recent years have seen significant advancements in exploring novel light-matter interactions such as hyperbolic dispersion within natural crystals. However, current studies have predominantly concentrated on local optical response of materials characterized by a dielectric tensor without spatial dispersion. Here, we investigate the nonlo- cal response in optically-active crystals with screw symmetries, revealing their lossless, super-dispersive properties compared to traditional optical response functions. We leverage this universal nonlocal dispersion, i.e. the dispersion of optical rotatory power, to explore a novel spectral de-multiplexing scheme compared to conventional gratings, prisms and metasurfaces. We design and demonstrate an ‘Nonlocal-Cam’ - a camera that exploits nonlocal dispersion through sampling of polarized spectral states and the application of computational spectral reconstruction algo- rithms. The Nonlocal-Cam captures information in both laboratory and outdoor field experiments which is unavailable to traditional intensity cameras - the spectral texture of polarization. Merging the fields of nonlocal electrodynam- ics and computational imaging, our work paves the way for exploiting nonlocal optics of optically active materials in a variety of applications, from biological microscopy to physics-driven machine vision and remote sensing. 1  Introduction Recent advancements in the study of light-matter inter- actions with natural crystals at the atomic scale have unveiled a variety of intriguing phenomena. These include the identification of hyperbolic polaritons in hBN [1–4], MoO3 [5–7], α-V2 O5 [8], WSe2 [9], and SnO2 [10], ghost polaritons in calcite [11], and hyperbolic shear polaritons in β-Ga2 O3 [12] and CdWO4 [13]. However, the majority of research has been confined to local opti- cal responses characterized by spatially non-dispersive dielectric tensors, limiting the exploration to phenom- ena exhibiting linearly polarized eigenstates. Addition- ally, the temporal dispersion of local responses can be captured by the Drude-Lorentz model with damped har- monic oscillators [14]. The Kramers-Kronig relations in the Drude-Lorentz model inherently suggests that the strong temporal dispersion of local dielectric functions is accompanied by large optical losses, further constraining the range of accessible phenomena. The exploration of nonlocal responses is crucial for overcoming these limitations and unlocking new regime of light-matter interactions. Nonlocal responses extend the possible eigenstates of these interactions to include circular polarization, allowing many intriguing phenom- ena especially those related to Weyl and Axion physics [15–21]. A notable category of nonlocal crystals is natu- ral optically active crystals such as α-quartz. Recent X-ray scattering experiments have demonstrated that the screw Open Access © The Author(s) 2024. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use,