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Abstract Subwavelength metasurfaces with responsive optical properties in the visible spectrum are of growing interest for applications in dynamic structural color and sensing. Introducing porosity into these structures is a promising route to enhance environmental and surface sensitivity, yet realizing deeply subwavelength porosity through conventional top‐down fabrication remains challenging due to limitations in achieving high aspect ratio nanoscale features. Here, mesoporous silicon metasurfaces (pSi‐MSs) supporting Fano guided‐mode resonances are reported, realized via a straightforward hybrid top‐down patterning and bottom‐up porosification approach. The resulting structures exhibit tunable resonances across the visible spectrum, vivid structural coloration, and dynamic color changes in response to environmental stimuli, including vapor and liquid interactions. By integrating laser illumination, colorimetric contrast for real‐time detection is further enhanced. Finally, label‐free refractive index sensing and real‐time small molecule detection are demonstrated using an integrated differential sensing design with microfluidic pSi‐MSs. These results establish the pSi‐MS as a versatile platform for responsive photonic devices, dynamic color modulation, and surface‐based chemical and biological sensing. More broadly, these results highlight the potential of hybrid top‐down and bottom‐up fabrication strategies for enabling the next generation of dynamic and environmentally responsive metasurfaces. 

Abstract Structural color, a phenomenon arising from nanoscale interactions of light with materials, has the potential to unveil biological, chemical, physical, and mechanical characteristics directly to human users with high spatiotemporal resolution. However, its impact is often constrained by challenges in perceptual differentiation of subtle color variations. Laser imaging is one promising approach for addressing these challenges, yet is typically optimized for amplifying physical signals rather than for the psychophysical nature of color perception. Here, we introduce complementary color laser illumination (C²LI) as an imaging technique that accesses enhanced psychophysical non‐linearities in chromatic color perception—effectively boosting perceived color differences by maximizing chromatic contrast sensitivity, without reliance on digital processing. We demonstrate C²LI enables perceptually enhanced sensing and imaging in tasks such as microfluidic refractometric sensing, phase contrast enhanced microscopy, and semiconductor inspection–allowing users to detect subtle changes in sample properties that could otherwise remain imperceptible. C²LI’s ability to harness the interplay of structured light, structural color, and the psychophysics of color perception offers a new pathway for enhancing the fidelity of sample analysis, optimized for color vision. This makes C²LI well‐suited for sensing and imaging applications ranging from environmental and biomedical diagnostics to semiconductor metrology and defect inspection. 

Abstract Porous materials and nanocomposites have emerged as promising media for constructing high performance, tunable, responsive, and versatile optical platforms, with applications spanning diffractive and waveguide optics, metasurfaces, photonic sensors, and structural coatings. Despite their potential, achieving precise control over the structural and optical properties of these materials has remained a significant challenge, often requiring complex fabrication processes and post‐lithography processing steps that limit scalability, sustainability, and practical implementation. In this work, upon the use of nanoimprinting of refractive index (NIRI) is reported to directly pattern mesoporous titania (pTiO₂) and achieve localized, compression‐based modulation of refractive index. Two formulations of sol‐gel derived pTiO₂thin films are interrogated, revealing tunable refractive indices ranging fromn ≈ 1.5 ton ≈ 2.2 at visible wavelengths in response to nanoimprinting‐induced compression. Using a variety of micro‐patterned stamps, the direct fabrication of planar diffractive and gradient index optics is demonstrated without any curing, etching, or post‐lithography processing steps. These findings demonstrate that direct imprinting of pTiO₂ is a sustainable and effective method for controlling refractive index and fabricating optical devices, paving the way for future advancements in the development of compression‐tuned optical materials and their diverse applications. 

Abstract Dynamic and responsive structural color devices present promising opportunities for sensing and display technologies, with applications including point‐of‐care diagnostics, portable/wearable sensors, and low‐power full‐color displays. However, it is often difficult to generate a large and quantitatively meaningful colorimetric response especially toward weak stimuli. Here, dual‐band hyperchromatic structural color (HSC) is presented as an approach to overcome these challenges. Within this framework, a dual‐band mesoporous silicon rugate filter metamaterial co‐designed is experimentally realized for use with a dichromatic (red/green) illuminant. This is shown to enable an amplified red‐to‐green color transition with a substantially smaller wavelength shift than conventional structural color devices, Δλ ≪ |λ_G–λ_R|, as well as a direct quantitative mapping between the observed chromaticity and the input stimulus. This approach is experimentally demonstrated for the spatiotemporally resolved sensing of refractometric stimuli including small‐molecules and volatile organic compounds (VOCs) with a ≈0.08 nm equivalent spectral resolution. This approach is entirely scanning‐free, enabled by simple color imaging, and does not require advanced spectroscopic (hyperspectral) imaging or interferometric imaging to obtain meaningful quantitative and spatiotemporally resolved information pertaining to the sensor's attributes. These results demonstrate dual‐band HSC as a promising approach for realizing low‐cost and high performance dynamic structural color devices and sensors. 

We introduce the design, fabrication, and experimental investigation of subwavelength Fano resonant porous silicon metasurfaces functioning on the principle of guided mode resonance. These metasurfaces exhibit promise for dynamic structural coloration and sensing applications. 

Production of flat optics incorporating subwavelength features, particularly at visible frequencies, remains a significant challenge. Here, we establish a framework for the design of effective medium metasurfaces (EMM), relying on nanoimprinting of mesoporous silicon to realize a patterned refractive indexn(x,y) corresponding to an arbitrary transmitted phase profileϕ(x,y). The method is used to design the stamp profile required to produce a Fresnel lens and the theoretical performance of the metalens is examined using the finite-difference time-domain method. Additionally, we demonstrate neural network aided Monte Carlo analysis as a method to model the effects of metasurface fabrications errors on EMM performance and process yield.