Mark Luitzen Brongersma

The inability to resolve closely spaced objects fundamentally limits the information accessible to optical imaging systems. In a recent study, a k -space superoscillation framework is introduced as an alternative route to far-field superresolution imaging. By engineering a nonlocal, angle-dependent transmission function, the approach effectively redistributes spatial-frequency content in momentum space, enabling enhanced separation of image features without narrowing the point spread function. Implemented via an inverse-designed multilayer metastructure, the concept is experimentally validated at microwave frequencies, achieving an approximately twofold improvement in resolution. By suppressing real-space sidebands and concentrating energy into the focal region, the k -space approach addresses key limitations of conventional real-space superoscillation. Despite remaining challenges, such as scalability and bandwidth constraints, this work highlights the growing role of inverse design in enabling unconventional optical functionalities and offers a promising pathway toward practical superresolution imaging systems.

Tissue-clearing techniques have transformed optical imaging of fixed specimens, yet their application to living systems remains limited by toxicity and removal of key tissue components. We recently demonstrated that absorbing molecules such as tartrazine can reversibly render live mouse skin transparent. Subsequently, it was reported that isotonic protein solutions can achieve ex vivo and in vivo cellular clearing. However, discrepancies remain regarding the optimal refractive index (RI) for live-cell clearing and the impact of elevated osmolality on cell viability. Here, using cultured mammalian cells, we systematically examine the dependence of optical contrast on medium RI and the effects of hyperosmolality. We find that, contrary to the recent report of an optimal RI of 1.36 ∼ 1.37 for suspended cells, densely packed adherent cells exhibit a monotonic decrease in phase contrast up to an RI of 1.41 with tartrazine. Moreover, even under highly hyperosmotic conditions (∼1200 mOsm/kg), cultured cells exhibit minimal deformation and negligible loss of viability for up to 30 min in the clearing solution. These results demonstrate that tartrazine enables effective live-cell clearing at RI up to 1.41 while preserving viability under elevated osmolality and motivate future studies to define optimal conditions for in vivo optical clearing.

Nanophotonic resonators can amplify weak molecular circular dichroism (CD) signals, but structural chirality from angle-dependent photoexcitation or collection may mask molecular chiroptical features. Here, we develop an achiral nanodisk array and angle-resolved spectral measurement approach that deconvolves molecular and substrate signals, enabling artifact-free chiroptical enhancement. Circular polarization-resolved momentum-space spectroscopy maps chiroptical response across wavelength and collection angle to simultaneously report intrinsic, molecular CD and extrinsic, nanostructure-induced signals in distinct optical channels. We design silicon nitride nanodisks which support a simulated ∼150-fold enhancement in the density of optical chirality averaged throughout the analyte-accessible region and spectrally aligned with thiocamphor's CD features. We validate the enhancement of low concentration and enantiomeric excess (ee) CD signals with the predicted spectral and angular sensitivity, down to 0.1 mM and across 1-25% ee. Our approach demonstrates momentum-resolved, metasurface-enhanced CD spectroscopy as a promising path to reliable, sensitive detection of molecular chirality and enantiomeric purity.

Dynamic control of visible light is crucial for technologies such as holographic displays and adaptive optics. Passive metasurfaces can shape wavefronts at the subwavelength scale, and active metasurfaces promise to extend this functionality into the temporal domain. However, existing metasurfaces for dynamic phase manipulation typically cannot deliver phase modulation across a broad range without causing variations in the scattering amplitude. Here, we use an inverse-design pipeline to numerically demonstrate a hybrid-2D excitonic metasurface platform offering independent amplitude and phase control in the visible regime. Harnessing the gate-tunable excitonic response of monolayer WS₂ retrieved from experiments, we design a π-phase modulator with a uniform amplitude profile. Adding a second tunable monolayer, we achieve independent control of the amplitude and phase over the full 0–2π phase range, which we leverage for a reconfigurable beam-steering metadevice. Our results demonstrate how hybrid-2D excitonic metasurfaces enable electrically tunable wavefront shaping in the visible regime.

Tissue-clearing techniques have transformed optical imaging of fixed specimens, yet their application to living systems remains limited by toxicity and removal of key tissue components. We recently demonstrated that absorbing molecules such as tartrazine can reversibly render live mouse skin transparent. Subsequently, it was reported that isotonic protein solutions can achieve ex vivo and in vivo cellular clearing. However, discrepancies remain regarding the optimal refractive index (RI) for live-cell clearing and the impact of elevated osmolality on cell viability. Here, using cultured mammalian cells, we systematically examine the dependence of optical contrast on medium RI and the effects of hyperosmolality. We find that, contrary to the recent report of an optimal RI of 1.36∼1.37 for suspended cells, densely-packed adherent cells exhibit a monotonic decrease in phase contrast up to an RI of 1.41 with tartrazine. Moreover, even under highly hyperosmotic conditions (∼1200 mOsm/kg), cultured cells exhibit minimal deformation and negligible loss of viability for up to 30 min in the clearing solution. These results demonstrate that tartrazine enables effective live-cell clearing at RI up to 1.41 while preserving viability under elevated osmolality, and motivate future studies to define optimal conditions for in vivo optical clearing. Graphical

The visual appearances of surfaces are influenced by their colour and texture. Although the creation and tuning of structural colours has been realized with nanostructures^1,2, achieving dynamic control over visual texture^3,4 remains challenging. Inspired by dynamic modulation of cephalopod skin^5,6, we develop polymer films with programmable surface textures. We bring these textures to life through immersion in different liquids that cause reversible local swelling/contraction to a degree that is determined by electron-beam irradiation. We show how standard electron-beam patterning tools can spatially encode arbitrary textures that can be hidden and shown on demand. Similarly, by modulating the topography of optical Fabry–Pérot cavities, we create colour patterns that can be continuously tuned with microfluidic control to achieve several distinct appearance states, allowing them to camouflage with different backgrounds. Finally, by creating multilayer devices, we demonstrate independent control of texture and colour in a single device, enabling a higher level of dynamic control over visual appearance.

Monolayer 2D semiconductors, such as WS2, exhibit uniquely strong light-matter interactions due to exciton resonances that enable atomically-thin optical elements. Similar to geometry-dependent plasmon and Mie resonances, these intrinsic material resonances offer coherent and tunable light scattering. Thus far, the impact of the excitons temporal dynamics on the performance of such excitonic metasurfaces remains unexplored. Here, we show how the excitonic decay rates dictate the focusing efficiency of an atomically-thin lens carved directly out of exfoliated monolayer WS2. By isolating the coherent exciton radiation from the incoherent background in the focus of the lens, we obtain a direct measure of the role of exciton radiation in wavefront shaping. Furthermore, we investigate the influence of exciton-phonon scattering by characterizing the focusing efficiency as a function of temperature, demonstrating an increased optical efficiency at cryogenic temperatures. Our results provide valuable insights in the role of excitonic light scattering in 2D nanophotonic devices.

Light scattering in biological tissue presents a significant challenge for deep in vivo imaging. Our previous work demonstrated the ability to achieve optical transparency in live mice using intensely absorbing dye molecules, which created transparency in the red spectrum while blocking shorter-wavelength photons. In this paper, we extend this capability to achieve optical transparency across the entire visible spectrum by employing molecules with strong absorption in the ultraviolet spectrum and sharp absorption edges that rapidly decline upon entering the visible spectrum. This color-neutral and reversible tissue transparency method enables optical transparency for imaging commonly used fluorophores in the green and yellow spectra. Notably, this approach facilitates tissue transparency for structural and functional imaging of the live mouse brain labeled with yellow fluorescent protein and GCaMP through the scalp and skull. We show that this method enables longitudinal imaging of the same brain regions in awake mice over multiple days during development. Histological analyses of the skin and systemic toxicology studies indicate minimal acute or chronic damage to the skin or body using this approach. This color-neutral and reversible tissue transparency technique opens opportunities for noninvasive deep-tissue optical imaging, enabling long-term visualization of cellular structures and dynamic activity with high spatiotemporal resolution and chronic tracking capabilities.