@article{21532, abstract = {Recent research in nanophotonics for scintillation-based imaging has demonstrated promising improvements in scintillator performance. In parallel, advances in nanophotonics have enabled wavefront control through metasurfaces, a capability that has transformed fields such as microscopy by allowing tailored control of optical propagation. This naturally raises the following question, which we address in this Perspective: can wavefront-control strategies be leveraged to improve scintillation-based imaging? To answer this question, we explore nanophotonic- and metasurface-enabled wavefront control in scintillators to mitigate image blurring arising from their intrinsically diffuse light emission. While depth-of-field extension in scintillation faces fundamental limitations absent in microscopy, this approach reveals promising avenues, including stacked scintillators, selective spatial-frequency enhancement, and X-ray energy-dependent imaging. These results clarify the key distinctions in adapting wavefront engineering to scintillation and its potential to enable tailored detection strategies.}, author = {Chen, Joshua and Vaidya, Sachin and Pajovic, Simo and Choi, Seou and Michaels, William and Martin-Monier, Louis and Hu, Juejun and Cogswell, Carol and Roques-Carmes, Charles and Soljačić, Marin}, issn = {2330-4022}, journal = {ACS Photonics}, number = {7}, pages = {1757–1766}, publisher = {American Chemical Society}, title = {{Wavefront engineering for scintillation-based imaging}}, doi = {10.1021/acsphotonics.5c03124}, volume = {13}, year = {2026}, } @article{20405, abstract = {Dielectric breakdown of physical vacuum (Schwinger effect) is the textbook demonstration of compatibility of Relativity and Quantum theory. Although observing this effect is still practically unachievable, its analogue generalizations have been shown to be more readily attainable. This paper demonstrates that a gapped Dirac semiconductor, methylammonium lead-bromide perovskite (MAPbBr3), exhibits analogue dynamic Schwinger effect. Tunneling ionization under deep subgap mid-infrared irradiation leads to intense photoluminescence in the visible range, in full agreement with quasi-adiabatic theory. In addition to revealing a gapped extended system suitable for studying the analogue Schwinger effect, this observation holds great potential for nonperturbative field sensing, i.e., sensing electric fields through nonperturbative light-matter interactions. First, this paper illustrates this by measuring the local deviation from the nominally cubic phase of a perovskite single crystal, which can be interpreted in terms of frozen-in fields. Next, it is shown that analogue dynamic Schwinger effect can be used for nonperturbative amplification of nonparametric upconversion process in perovskites driven simultaneously by multiple optical fields. This discovery demonstrates the potential for material response beyond perturbation theory in the tunneling regime, offering extremely sensitive light detection and amplification across an ultrabroad spectral range not accessible by conventional devices.}, author = {Lorenc, Dusan and Volosniev, Artem and Zhumekenov, Ayan A. and Lee, Seungho and Ibáñez, Maria and Bakr, Osman M. and Lemeshko, Mikhail and Alpichshev, Zhanybek}, issn = {2330-4022}, journal = {ACS Photonics}, number = {9}, pages = {5220--5230}, publisher = {American Chemical Society}, title = {{Observation of analogue dynamic Schwinger effect and non-perturbative light sensing in lead halide perovskites}}, doi = {10.1021/acsphotonics.5c01360}, volume = {12}, year = {2025}, } @article{21530, abstract = {Metasurfaces, ultrathin structures composed of subwavelength optical elements, have revolutionized light manipulation by enabling precise control over electromagnetic waves’ amplitude, phase, polarization, and spectral properties. Concurrently, computational imaging leverages algorithms to reconstruct images from optically processed signals, overcoming the limitations of traditional imaging systems. This Perspective explores the synergistic integration of metaoptics and computational imaging, “metaoptic computational imaging”, which combines the physical wavefront shaping ability of metasurfaces with advanced computational algorithms to enhance imaging performance beyond conventional limits. We discuss how metaoptic computational imaging addresses the inherent limitations of single-layer metasurfaces in achieving multifunctionality without compromising efficiency. By treating metasurfaces as physical preconditioners and codesigning them with reconstruction algorithms through end-to-end (inverse) design, it is possible to jointly optimize the optical hardware and computational software. Advanced applications and new frontiers in the field enabled by metaoptic computational imaging are highlighted, including phase imaging and quantum state measurement.}, author = {Roques-Carmes, Charles and Wang, Kai and Yang, Yuanmu and Majumdar, Arka and Lin, Zin}, issn = {2330-4022}, journal = {ACS Photonics}, keywords = {nanophotonics, metasurfaces, computational imaging, inverse design}, number = {4}, pages = {1722--1733}, publisher = {American Chemical Society}, title = {{Metaoptic computational imaging}}, doi = {10.1021/acsphotonics.4c02266}, volume = {12}, year = {2025}, } @article{21531, abstract = {Entanglement is a unique feature of quantum mechanics. In coupled systems of light and matter, entanglement manifests itself in the linear superposition of multipartite quantum states (e.g., parametrized by the multiple spatial, spectral, or temporal degrees of freedom of a light field). In bipartite systems, the Schmidt decomposition provides a modal decomposition of the entanglement structure over independent, separable states. Although ubiquitous as a mathematical tool to describe and measure entanglement, there exists no general efficient experimental method to decompose a bipartite quantum state onto its Schmidt modes. Here, we propose a method that relies on bipartite self-configuring optics that automatically ``learns'' the Schmidt decomposition of an arbitrary pure quantum state. Our method is agnostic to the degrees of freedom over which quantum entanglement is distributed and can reconstruct the Schmidt modes and values by variational optimization of the network's output powers or coincidences. We illustrate our method with numerical examples of spectral entanglement analysis for biphotons generated via spontaneous parametric down conversion and provide experimental guidelines for its realization, including the influence of losses and impurities. Our method provides a versatile and scalable way of analyzing entanglement in bipartite integrated quantum photonic systems. }, author = {Roques-Carmes, Charles and Karnieli, Aviv and Miller, David A. B. and Fan, Shanhui}, issn = {2330-4022}, journal = {ACS Photonics}, keywords = {integrated photonics, spontaneous parametric down conversion, entanglement, quantum teleportation, reconfigurable optics}, number = {6}, pages = {3285--3294}, publisher = {American Chemical Society}, title = {{Automated modal analysis of entanglement with bipartite self-configuring optics}}, doi = {10.1021/acsphotonics.5c00813}, volume = {12}, year = {2025}, } @article{17479, abstract = {Phonon polaritons (PhPs), light coupled to lattice vibrations, in the highly anisotropic polar layered material molybdenum trioxide (α-MoO3) are currently the focus of intense research efforts due to their extreme subwavelength field confinement, directional propagation, and unprecedented low losses. Nevertheless, prior research has primarily concentrated on exploiting the squeezing and steering capabilities of α-MoO3 PhPs, without inquiring much into the dominant microscopic mechanism that determines their long lifetimes, which is key for their implementation in nanophotonic applications. This study delves into the fundamental processes that govern PhP damping in α-MoO3 by combining ab initio calculations with scattering-type scanning near-field optical microscopy (s-SNOM) and Fourier transform infrared (FTIR) spectroscopy measurements across a broad temperature range (8–300 K). The remarkable agreement between our theoretical predictions and experimental observations allows us to identify third-order anharmonic phonon–phonon scattering as the main damping mechanism of α-MoO3 PhPs. These findings shed light on the fundamental limits of low-loss PhPs, which is a crucial factor for assessing their implementation into nanophotonic devices.}, author = {Taboada-Gutiérrez, Javier and Zhou, Yixi and Tresguerres-Mata, Ana I.F. and Lanza, Christian and Martínez-Suárez, Abel and Álvarez-Pérez, Gonzalo and Duan, Jiahua and Martín, José Ignacio and Vélez, María and Prieto Gonzalez, Ivan and Bercher, Adrien and Teyssier, Jérémie and Errea, Ion and Nikitin, Alexey Y. and Martín-Sánchez, Javier and Kuzmenko, Alexey B. and Alonso-González, Pablo}, issn = {2330-4022}, journal = {ACS Photonics}, number = {9}, pages = {3570--3577}, publisher = {American Chemical Society}, title = {{Unveiling the mechanism of phonon-polariton damping in α‑MoO3}}, doi = {10.1021/acsphotonics.4c00485}, volume = {11}, year = {2024}, } @article{21528, abstract = {We present a framework for the end-to-end optimization of metasurface imaging systems that reconstruct targets using compressed sensing, a technique for solving underdetermined imaging problems when the target object exhibits sparsity (e.g., the object can be described by a small number of nonzero values, but the positions of these values are unknown). We nest an iterative, unapproximated compressed sensing reconstruction algorithm into our end-to-end optimization pipeline, resulting in an interpretable, data-efficient method for maximally leveraging metaoptics to exploit object sparsity. We apply our framework to super-resolution imaging and high-resolution depth imaging with a phase-change material. In both situations, our end-to-end framework effectively optimizes metasurface structures for compressed sensing recovery, automatically balancing a number of complicated design considerations to select an imaging measurement matrix from a complex, physically constrained manifold with millions of dimensions. The optimized metasurface imaging systems are robust to noise, significantly improving over random scattering surfaces and approaching the ideal compressed sensing performance of a Gaussian matrix, showing how a physical metasurface system can demonstrably approach the mathematical limits of compressed sensing.}, author = {Arya, Gaurav and Li, William F. and Roques-Carmes, Charles and Soljačić, Marin and Johnson, Steven G. and Lin, Zin}, issn = {2330-4022}, journal = {ACS Photonics}, keywords = {end-to-end, optimization, metasurface, imaging, compressed sensing}, number = {5}, pages = {2077--2087}, publisher = {American Chemical Society}, title = {{End-to-end optimization of metasurfaces for imaging with compressed sensing}}, doi = {10.1021/acsphotonics.4c00259}, volume = {11}, year = {2024}, } @article{21672, abstract = {We present a framework for the end-to-end optimization of metasurface imaging systems that reconstruct targets using compressed sensing, a technique for solving underdetermined imaging problems when the target object exhibits sparsity (i.e. the object can be described by a small number of non-zero values, but the positions of these values are unknown). We nest an iterative, unapproximated compressed sensing reconstruction algorithm into our end-to-end optimization pipeline, resulting in an interpretable, data-efficient method for maximally leveraging metaoptics to exploit object sparsity. We apply our framework to super-resolution imaging and high-resolution depth imaging with a phase-change material. In both situations, our end-to-end framework computationally discovers optimal metasurface structures for compressed sensing recovery, automatically balancing a number of complicated design considerations to select an imaging measurement matrix from a complex, physically constrained manifold with millions ofdimensions. The optimized metasurface imaging systems are robust to noise, significantly improving over random scattering surfaces and approaching the ideal compressed sensing performance of a Gaussian matrix, showing how a physical metasurface system can demonstrably approach the mathematical limits of compressed sensing.}, author = {Arya, Gaurav and Li, William F. and Roques-Carmes, Charles and Soljačić, Marin and Johnson, Steven G. and Lin, Zin}, issn = {2330-4022}, journal = {ACS Photonics}, keywords = {end-to-end, optimization, metasurface, imaging, compressed sensing}, publisher = {American Chemical Society}, title = {{End-to-end optimization of metasurfaces for imaging with compressed sensing}}, doi = {10.1021/acsphotonics.4c00259}, year = {2024}, } @article{21529, abstract = {A central challenge in the emerging field of free-electron quantum optics is to achieve strong quantum interaction and single-photon nonlinearity between a flying free electron and a photonic mode. Existing schemes are intrinsically limited by electron diffraction, which puts an upper bound on the interaction length and, therefore, on the strength of quantum coupling and nonlinearity. Here, we propose “free-electron fibers”: effectively one-dimensional photonic systems where free electrons copropagate with two guided modes. The first mode applies a ponderomotive trap to the free electron, removing the limitations due to electron diffraction. The second mode strongly couples to the guided free electron with an enhanced coupling that is orders of magnitude larger than previous designs. The extended interaction lengths enabled by our scheme allow for strong single-photon nonlinearities mediated by free electrons. We predict novel quantum effects in our system such as deterministic single-photon emission and nonlinear multimode dynamics. Our proposal paves the way toward the realization of heralded macroscopic nonclassical light generation, deterministic single-photon sources, and quantum gates controlled by free-electron–photon interactions.}, author = {Karnieli, Aviv and Roques-Carmes, Charles and Rivera, Nicholas and Fan, Shanhui}, issn = {2330-4022}, journal = {ACS Photonics}, keywords = {quantum optics, free electrons, single photon nonlinearity, electron-photon interaction}, number = {8}, pages = {3401--3411}, publisher = {American Chemical Society}, title = {{Strong coupling and single-photon nonlinearity in free-electron quantum optics}}, doi = {10.1021/acsphotonics.4c00908}, volume = {11}, year = {2024}, } @article{21527, abstract = {Optical metasurfaces have been heralded as the platform to integrate multiple functionalities in a compact form-factor, with the potential to replace bulky optical components. A central stepping stone toward realizing this promise is the demonstration of multifunctionality under several constraints (e.g., at multiple incident wavelengths and/or angles) in a single device, an achievement being hampered by design limitations inherent to single-layer planar geometries. Here, we propose a framework for the inverse design of multilayer metaoptics via topology optimization, showing that even few-wavelength thick devices can achieve high-efficiency multifunctionality, such as multiangle light concentration and plan-achromaticity. We embody our framework in multiple closely spaced patterned layers of a low-index polymer, with fabrication constraints specific to this platform enforced in the optimization process. We experimentally demonstrate our approach with an inverse-designed 3D-printed light concentrator working at five different nonparaxial angles of incidence. Our framework paves the way toward realizing multifunctional ultracompact 3D nanophotonic devices.}, author = {Roques-Carmes, Charles and Lin, Zin and Christiansen, Rasmus E. and Salamin, Yannick and Kooi, Steven E. and Joannopoulos, John D. and Johnson, Steven G. and Soljačić, Marin}, issn = {2330-4022}, journal = {ACS Photonics}, keywords = {metasurfaces, inverse design, multilayered metaoptics, 3D printing, topology optimization}, number = {1}, pages = {43--51}, publisher = {American Chemical Society}, title = {{Toward 3D-printed inverse-designed metaoptics}}, doi = {10.1021/acsphotonics.1c01442}, volume = {9}, year = {2022}, } @article{21525, abstract = {We present a novel design for an ultracompact, passive light source capable of generating ultraviolet and X-ray radiation, based on the interaction of free electrons with the magnetic near-field of a ferromagnet. Our design is motivated by recent advances in the fabrication of nanostructures, which allow the confinement of large magnetic fields at the surface of ferromagnetic nanogratings. Using ab initio simulations and a complementary analytical theory, we show that highly directional, tunable, monochromatic radiation at high frequencies could be produced from relatively low-energy electrons within a tabletop design. The output frequency is tunable in the extreme ultraviolet to hard X-ray range via electron kinetic energies from 1 keV to 5 MeV and nanograting periods from 1 μm to 5 nm. The proposed radiation source can achieve the tunability and monochromaticity of current free-electron-driven sources (free-electron lasers, synchrotrons, and laser-driven undulators), yet with a significantly reduced scale, cost, and complexity. Our design could help realize the next generation of tabletop or on-chip X-ray sources.}, author = {Fisher, Sophie and Roques-Carmes, Charles and Rivera, Nicholas and Wong, Liang Jie and Kaminer, Ido and Soljačić, Marin}, issn = {2330-4022}, journal = {ACS Photonics}, keywords = {X-ray sources, free electrons, nanostructure, undulator, synchrotron, free-electron laser}, number = {5}, pages = {1096--1103}, publisher = {American Chemical Society }, title = {{Monochromatic X-ray source based on scattering from a magnetic nanoundulator}}, doi = {10.1021/acsphotonics.0c00121}, volume = {7}, year = {2020}, } @article{21533, abstract = {Recent advances in the fabrication of nanostructures and nanoscale features in metasurfaces offer new prospects for generating visible light emission from low-energy electrons. Here we present the experimental observation of visible light emission from low-energy free electrons interacting with nanoscale periodic surfaces through the Smith–Purcell (SP) effect. We demonstrate SP light emission from nanoscale gratings with periodicity as small as 50 nm, enabling the observation of tunable visible radiation from low-energy electrons (1.5 to 6 keV), an order of magnitude lower in energy than previously reported. We study the emission wavelength and intensity dependence on the grating pitch and electron energy, showing agreement between experiment and theory. Our results open the way to the production of SP-based nanophotonics integrated devices. Built inside electron microscopes, SP sources could enable the development of novel electron–optical correlated spectroscopic techniques and facilitate the observation of new quantum effects in light sources.}, author = {Massuda, Aviram and Roques-Carmes, Charles and Yang, Yujia and Kooi, Steven E. and Yang, Yi and Murdia, Chitraang and Berggren, Karl K. and Kaminer, Ido and Soljačić, Marin}, issn = {2330-4022}, journal = {ACS Photonics}, keywords = {light−matter interactions, periodic structures, nanophotonics, free-electron light sources}, number = {9}, pages = {3513--3518}, publisher = {American Chemical Society }, title = {{Smith–Purcell radiation from low-energy electrons}}, doi = {10.1021/acsphotonics.8b00743}, volume = {5}, year = {2018}, }