Optics
Bayesian Optimization for Practical H2 Sensors: Inverse Design of Pd-based Plasmonic Metasurfaces
Pernilla Ekborg-Tanner, Athanasios Theodoridis, Joachim Fritzsche et al. (+3 more)
Hydrogen detection is becoming increasingly important as its use grows across energy and industrial systems. Optical sensing platforms based on palladium (Pd) nanoparticles are attractive for this task because hydrogen uptake directly alters their plasmonic response. Organizing such nanoparticles into periodic two-dimensional arrays, known as metasurfaces, further enhances their optical response through collective resonances. However, the large design space presented by chemical composition, nanoparticle geometry, and array structure calls for systematic approaches for optimizing complex nanoalloy metasurface geometries. Here, we develop an inverse-design framework based on
Bayesian optimization that couples first-principles dielectric functions with electromagnetic simulations to identify high-performance PdAu nanodisk arrays for hydrogen sensing in the 1 to 100 mbar range where the flammability of H2 becomes a concern. We use our approach to search a five-dimensional design space, comprising nanodisk height and radius, array pitch,
polymer coating thickness, and Au fraction in order to maximize the H-induced change in extinction at a single wavelength of choice. The results show that integrating first-principles optical models with data-efficient optimization yields experimentally feasible nanoparticle metasurfaces tailored for targeted hydrogen pressures, while providing a pathway to future multiobjective sensor design. They also reveal remaining gaps in the modeling methodologies that still limit the quantitative reliability of the approach.
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All authors Pernilla Ekborg-Tanner, Athanasios Theodoridis, Joachim Fritzsche, Christoph Langhammer, Andrea Baldi, Paul Erhart
Optics
Toward Topology-Optimized Foundry PDKs: A Seeded Design Framework for Multimode Interferometers
Jacob M. Hiesener, Archana Kaushalram, Joshua J. Wong et al. (+2 more)
We present an end-to-end design methodology for multimode interferometer (MMI)-based photonic devices that combines parameter optimization (PO) on analytical models with seeded
topology optimization (TO) to maximize performance while preserving foundry design-rule compliance. A PO seed device is further refined via seeded TO, accessing a larger design space than analytical or parameterized methods alone can reach. We validate this pipeline on a 1x2 splitter, a TE modal multiplexer, and a polarization splitter, fabricating and measuring the first two on a commercial foundry process. Seeded TO reduces the measured insertion loss of the 1x2 splitter from 0.20 to 0.14 dB and improves TE00 transmission of the modal multiplexer from -2.79 to -1.01 dB over O-band. Applying this pipeline to a commercial foundry process design kit (PDK)-provided 1x2 and 2x2 splitter improves simulated transmission and tightens the 2x2 splitting ratio from 0.524 to 0.506, along with improved fabrication robustness, offering a practical, foundry-validated route toward incorporating TO-designed components into commercial PDKs.
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All authors Jacob M. Hiesener, Archana Kaushalram, Joshua J. Wong, Robert P. Pesch, Stephen E. Ralph
Optics
Ultra-broadband integrated optical parametric amplifier for quantum sensing
Kai-Chi Chang, Tushar Sanjay Karnik, Chun-Ho Lee et al. (+9 more)
Although thin-film lithium niobate (TFLN) facilitates efficient signal generation and nonlinear and
quantum interactions, the realization of optical parametric amplification (OPA) that can provide simultaneous ultra-broadband and high-gain operation in an integrated chip continues to pose a challenge. Here we demonstrate continuous-wave-pumped OPA in an X-cut MgO-doped, dispersion-engineered, and adaptively-poled TFLN waveguide of 1.6 cm length, achieving a flat-top profile covering a 450 nm-wide optical wavelength window, corresponding to a 3-dB gain bandwidth of about 56 THz. Among reported TFLN platforms, our device exhibits the broadest 3-dB gain bandwidth. The same device can be pumped either directly at visible wavelengths through second-order x(2) interactions or in the telecom band through cascaded x(2) processes, the latter eliminating the need for a high-power visible pump
laser. We achieve maximum gains of 8.87 +- 0.39 dB and 10.79 +- 0.43 dB at on-chip pump powers of 74 mW and 170 mW for the direct and cascaded schemes, respectively. We further directly probe OPA gain across the 1650-1900 nm wavelength range, where experimental gain measurements have remained scarce. With a normalized on-chip gain of 1.21 dB per W per mm, our device sets a new
benchmark among reported cascaded x(2) nonlinear processes. This work advances the realization of integrated optical parametric amplifiers, offering high efficiency, robust gain, ultra-broadband bandwidth, and continuous-wave operation, thereby enabling new capabilities for next-generation
quantum sensing and photonic systems.
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All authors Kai-Chi Chang, Tushar Sanjay Karnik, Chun-Ho Lee, Kiyoung Ko, Xinyi Ren, Ian Christen, Reshma Kopparapu, Clayton Cheung, Kiwon Kwon, Kamila Kunes, Zaijun Chen, Mengjie Yu
Optics
A Comprehensive Review of Large Language Models for Nanophotonics: From Surrogate Modeling to Autonomous Design
Huanshu Zhang, Kegeng Tang, Lei Kang et al. (+3 more)
Metasurfaces have revolutionized the development of photonic devices by enabling unprecedented precision in light manipulation. However, their design processes are often constrained by computationally expensive simulations and complex high-dimensional design spaces. Although deep learning has accelerated the design process by serving as a surrogate model, it remains constrained by task-specific architectures and lacks universal
reasoning capabilities. This review surveys how Large
Language Models (LLMs) are adding semantic interfaces, code generation, and tool orchestration to established numerical nanophotonic workflows. We first outline the development from classical neural networks to
transformer-based models and their applications in nanophotonic design. We then review the emergence of LLM-related methods in nanophotonics and organize them into two operational modes: surrogate models that treat structure-spectrum mapping as a
language task, and agentic systems that have been demonstrated to generate code, orchestrate selected simulation steps, and support closed-loop optimization. Furthermore, to identify future cross-disciplinary opportunities, we briefly explore applications of LLMs in research fields such as materials science and wireless communications. This review concludes by looking ahead to the next generation of
multimodal foundation models with physical perception capabilities. In this
vision, artificial intelligence is evolving from passive tools into active collaborators, participating in autonomous scientific discovery.
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All authors Huanshu Zhang, Kegeng Tang, Lei Kang, Sawyer D. Campbell, Zihao Wang, Douglas H. Werner
Optics
A compact low-frequency optomechanical triaxial inertial sensor
Daniel George, Jose D. Hernandez Rivero, Moritz Mehmet et al. (+5 more)
Triaxial optomechanical accelerometers offer compact, ground-testable alternatives to electrostatic sensors for satellite geodesy, seismometry, and various other applications. We demonstrate a low-CSWaP triaxial sensor using monolithic fused-silica resonators with dual heterodyne interferometric readout. The X axis reaches a 60~pico-g/$\sqrt{\mathrm{Hz}}$ readout noise floor, and the in-plane axes resolve ambient seismic ground motion in agreement with a co-located commercial seismometer from 4~mHz to 8~Hz. The Z axis exhibits higher noise under $1g$ loading due to
gravity-induced
geometric stiffening (44.45~Hz versus 11.07~Hz in a 0g-equivalent configuration), with measurements indicating in-orbit performance on par with the in-plane sensors. These results support the feasibility of triaxial optomechanical accelerometry for space missions and ground-based applications.
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All authors Daniel George, Jose D. Hernandez Rivero, Moritz Mehmet, Ramses Miranda Espino, Xiangyu Guo, Andrea Nelson, Jose Sanjuan, Felipe Guzman
Optics
Conservation of Pseudoangular Momentum in the Radiative Emission and Optical Excitation of Valley-Polarized Surface Lattice Resonances
Siamak Khorasani, Marc R. Bourgeois and David J. Masiello
Surface
lattice resonances (SLRs) are collective polaritonic excitations in nanoparticle arrays, with band-edge states enabling
symmetry-based control of radiation including scattering, photoluminescence, conventional and polariton lasing, and condensation. Here, we show that the integer pseudoangular momentum (PAM) of valley-polarized SLRs in parity-broken hexagonal arrays of honeycomb and kagome arrangements is directly encoded in the phase and polarization structure of their emitted electromagnetic fields. The effects of parity-
symmetry breaking on SLR PAM and the localized surface plasmon angular momentum associated with the individual nanoparticles composing the array are investigated, and an explicit link between these quantities is established. Leveraging electromagnetic reciprocity, we further propose a structured optical field possessing the same array
symmetries and integer PAM as the underlying SLRs and demonstrate theoretically and numerically that it selectively couples to valley-polarized SLRs with matching quantized PAM. Our results establish PAM-resolved light-matter interactions involving
lattice resonances as providing new opportunities for
symmetry-selective nanophotonic control, chiral light generation, and angular-momentum-engineered metasurfaces.
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Optics
Robust Orbital Angular Momentum Transfer Using Low-Cost Diffractive Optics
Beatriz Morales-Cruzado, Benjamin Perez-Garcia, Francisco G. Peérez Gutiérrez et al. (+1 more)
Reliable transfer of orbital angular momentum (OAM) to microscopic objects typically relies on high-fidelity
vortex beams generated by programmable spatial light modulators or precision-fabricated phase optics. Here, we demonstrate that robust OAM transfer in optical tweezers can be achieved using static binary holograms printed on acetate substrates. The printed diffractive optics generate Laguerre-Gaussian
vortex beams with sufficient spatial fidelity to induce controlled optical torque and stable rotational manipulation of polystyrene microspheres in a high-numerical-aperture optical tweezers system. Despite a diffraction efficiency of only approximately 2%, the generated beams enable reproducible particle rotation using less than 1 mW of optical power in the first diffraction order. The rotational dynamics were systematically characterized as a function of incident optical power and topological charge, revealing the expected increase in angular velocity with both parameters, consistent with OAM-driven torque in the overdamped regime. These results demonstrate that efficient optical angular momentum transfer is remarkably tolerant to the reduced efficiency of passive printed diffractive optics, establishing a robust, scalable, and high-damage-threshold platform for structured-light optical manipulation with applications in microfluidics, biophysics, optomechanics, and optical trapping.
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All authors Beatriz Morales-Cruzado, Benjamin Perez-Garcia, Francisco G. Peérez Gutiérrez, Carmelo Rosales-Guzmán
Optics
Neutron Interferometers from Stacked Holographic Photopolymer Gratings
Saba Shams-Lahijani, Tobias Jenke, Juergen Klepp et al. (+2 more)
Long-wavelength
neutron interferometry using discrete optical elements is notoriously challenging due to stringent
alignment and stability requirements. Here, we introduce a monolithic double-Laue
neutron interferometer fabricated from a stack of commercial Bayfol HX photopolymer films. By recording holographic gratings simultaneously in multiple layers, we create a robust device that is inherently aligned, bypassing traditional stability problems. We demonstrate the device's function by observing the characteristic interference fringes in the diffracted intensity of both light and very cold
neutrons. The interferometer is then used to perform in-situ characterization of the
neutron beam's spectral profile, demonstrating its utility as a compact spectrometer. Our work establishes stacked holographic gratings as a simple, versatile, and powerful platform for matter-wave interferometry and metrology.
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All authors Saba Shams-Lahijani, Tobias Jenke, Juergen Klepp, Christian Pruner, Martin Fally
Optics
Real-time estimation of the transmission matrix of an atmospheric channel
Cade Peters, Raphael Bellossi, Douglas McDonald et al. (+3 more)
Optical wavelengths have received significant
attention in free-space channels and are vital for applications in communications, imaging and sensing. Their widespread implementation is motivated by a variety of factors including improved bandwidths, increased security and higher energy efficiency. However, these advantages cannot be fully brought to bear in real-world scenarios due to the deleterious effects of atmospheric
turbulence. Induced by small temperature and pressure fluctuations in the environment that vary rapidly in space and time, these effects cause significant power losses which decrease SNR, induce severe crosstalk in communication links, and greatly limit resolution of long-range imaging systems. To overcome this, we numerically and experimentally investigate the reconstruction of the transmission
matrix of a time-evolving atmospheric channel with a real-time recursive optimization routine. We demonstrate that this estimation technique is able to keep up with the
evolution of the channel and enables a significant improvement of communication-relevant quantities such as the coupling of the received light into a single-mode fiber while notably reducing the probability and duration of power outages, even in strong
turbulence. Our results have immediate applications in free-space optical communication in both the classical and
quantum regimes.
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All authors Cade Peters, Raphael Bellossi, Douglas McDonald, Andrew Forbes, Szymon Gladysz, Giacomo Sorelli
Optics · Cross-listed from quant-ph
Single-atom detection with a quantum-controlled mechanical oscillator
Maxime Perdriat, Maciej Dziewiecki, Josef-Anton Agner et al. (+4 more)
Using supersonic expansion, we create a time-gated, directional beam of Xe atoms with a narrow momentum distribution and detect their collisions with a levitated nanosphere cooled to its
quantum ground state. We observe individual momentum kicks below 50 keV/c with 96% confidence and distinguish directional momentum transfer from the atomic beam against the background of thermal collisions. Our experiments constitute a first step toward the exploration of distance-dependent short-range interactions between atoms and levitated systems, as well as toward the use of levitated platforms for impulsive force sensing in previously unexplored parameter regimes.
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All authors Maxime Perdriat, Maciej Dziewiecki, Josef-Anton Agner, Massimiliano Rossi, Frederic Merkt, Martin Frimmer, Lukas Novotny
Optics
Body-of-Revolution Finite-Element Model of Plasmon-Enhanced Fluorescence
Luke C. Ugwuoke, Farooq Kyeyune and Tjaart P. J. Krüger
Plasmon-enhanced fluorescence (PEF) is one of the most widely investigated optical phenomena in hybrid systems of emitters and plasmonic nanoantennas, with applications ranging from biosensing to single-molecule emission microscopy. In this work, we extend finite-element modelling of PEF beyond spherically symmetric geometries using a body-of-revolution finite-element method (BOR-FEM). By exploiting exact or equivalent rotational
symmetry, 3D emitter-nanoantenna systems are reduced to computationally efficient 2D formulations while retaining the essential electromagnetic interactions governing excitation and emission. We validate the framework against three previously investigated emitter-nanorod systems, including one requiring an equivalent axisymmetric
geometric transformation, before applying it to an emitter-core-shell nanorod system. Specifically, we investigate the PEF of the terminal chlorophyll emitter of the major plant light-harvesting complex (LHCII), the most abundant membrane
protein on Earth, interacting with a gold core-dielectric shell nanorod with one or two dielectric shells. The simulations reveal that the interplay between excitation enhancement, radiative-rate enhancement, and non-radiative Ohmic losses gives rise to four distinct shell-thickness-dependent operating regimes (quenching, enhancement, suppression, and decoupling), with recovery of the intrinsic
quantum yield in the decoupling regime. The predicted enhancement factors for experimentally relevant dual-shell nanorods agree well with previously reported measurements. These results establish BOR-FEM as an efficient and versatile framework for modelling PEF in rotationally-symmetric nanoantenna geometries and in non-axisymmetric geometries that admit equivalent axisymmetric representations, providing a practical route for the rational design and optimisation of plasmon-enhanced bio-nanophotonic systems.
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Optics · Cross-listed from cond-mat.quant-gas
KPZ scaling in one-dimensional arrays of photon condensates
Michiel Yzewyn and Michiel Wouters
Bose-Einstein condensates of
photons in dye filled microcavities are known to feature many properties of the ideal bose gas at thermal
equilibrium. Nevertheless, the finite
photon life time renders them driven dissipative systems where losses are balanced by continuous driving by a pump
laser. We show here with simulations based on a classical field model that their driven-dissipative nature causes their first order coherence to feature Kardar-Parisi-Zhang (KPZ) scaling, a phenomenon well known in the related condensates of
exciton-polaritons. Remarkably, we find that the KPZ scaling even occurs in a regime with large density fluctuations. We discuss the modification of the scaling by the occupation of excited states and how to recover the universal scaling behavior by spectral filtering.
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Optics
Parallel single-pixel imaging based on modulation region expansion and overlapping reconstruction
Yinran Shen, Xuri Yao, Shijian Li et al. (+4 more)
Parallel single-pixel imaging (PSPI) enhances the data acquisition efficiency of single-pixel imaging, but its reconstruction quality depends on a cumbersome and noise-sensitive calibration process. To address this challenge, a PSPI strategy was introduced that leverages modulation region expansion and overlapping reconstruction. This method results in the calibration of modulation of the subregion for each detector, enabling robust operations with undersampled data. It compensates for misalignment via modulation region expansion and overlapping reconstruction, achieving seamless and high-quality imaging that surpasses conventional PSPI in simulations and experiments. Furthermore, this strategy exhibits remarkable robustness, maintaining high imaging quality under extremely nonideal conditions, such as large deflection angles between the array detector and the modulator. This work provides a simple, efficient, and robust framework that simplifies the PSPI workflow and offers broad applicability in high-resolution, high-speed computational imaging.
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All authors Yinran Shen, Xuri Yao, Shijian Li, Chao Shen, Yuhao Wang, Chongwu Shao, Qing Zhao
Optics
The vanishing distance: a depth-range boundary for dynamic wavefront shaping
Hugo Lassiette, Léa Testé, Léa Krafft et al. (+6 more)
Optical imaging and transmission through scattering media conventionally rely on ballistic light, whose power decays exponentially with the optical thickness. Although ballistic light cannot be exploited beyond a certain depth, no simple criterion currently identifies this limit. Therefore, we introduce here the vanishing distance that is defined as the propagation length at which the ballistic power equals the power carried by a single diffuse optical mode. Beyond the vanishing distance, multiply scattered light dominates, which can be harnessed by optical wavefront shaping or by computational reconstructions. We present a simple semi-analytical model for radiance propagation, validated by Monte Carlo simulations and by experiments in both monodisperse and heterogeneous scattering media. From these data, we estimate the vanishing distance and the associated minimum source power. Across representative scattering environments, ballistic light vanishes after about 20 to 40 scattering mean free paths. Unlike the transport mean free path that characterizes the angular randomization of the scattered light, the vanishing distance identifies the loss of the ballistic channel on a modal-power basis. The vanishing distance is thus a two-sided bound: ballistic approaches cannot be efficiently applied beyond it, whereas wavefront shaping of scattered light offers no advantage below it.
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All authors Hugo Lassiette, Léa Testé, Léa Krafft, Geoffrey Maulion, Vincent Michau, Romain Pierrat, Sébastien Popoff, Willem L. Vos, Serge Meimon
Optics · Cross-listed from quant-ph
Engineering of Dual Wavelength, Polarization Selective Metalenses in Silicon Carbide
Xiaoying Huang, Ziwei Yang, Konosuke Shimazaki et al. (+7 more)
Spin defects in silicon carbide (SiC) are promising candidates for integrated
quantum photonics, offering long-lived
spin states and near-infrared emission suitable for low-loss photonic integration and fibre-based
quantum communication. However, light extraction from these defects remains challenging due the relatively high refractive index of SiC. Metalenses offer a compact approach to enhance light collection by engineering the wavefront directly at the material interface. Here, we design and fabricate monolithic metalenses from SiC bulk material that simultaneously operate at 860 and 1240 nm, matching with emission from the nitrogen vacancy and silicon vacancy colour centers. By independently engineering the phase response at both wavelengths, the metalens enables collection and polarization manipulation of the emitted light. We further employ the metalenses to demonstrate optically detected
magnetic resonance of both defects simultaneously. These multifunctional metalenses provide a compact optical interface for scalable integrated SiC photonic devices.
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All authors Xiaoying Huang, Ziwei Yang, Konosuke Shimazaki, Kritsana Saego, Otto Cranwell Schaeper, Evan Williams, Dragomir Neshev, Hark Hoe Tan, Igor Aharonovicha, Mehran Kianinia
Optics
Fiber Nonlinearity Compensation of Coherent Signals Using Deep Photonic Reservoir Computer
Yi-Wei Shen, Rui-Qian Li, Zheng-Can Sun et al. (+4 more)
Photonic reservoir computer (PRC) is a promising optical computing framework for high-speed optical signal processing, and various reports have shown its functionality of linear equalization for intensity-modulation direct-detection communication links. However, coherent communication links suffer more from nonlinear impairment, whereas its nonlinear equalization is very challenging. Here we demonstrate the nonlinear equalization of coherent 16-level quadrature amplitude modulation (16-QAM) signals using a deep PRC in experiment. The deep PRC consists of cascading injection-locked
semiconductor lasers with optical feedback loops. For 16-QAM signals with a transmission rate of 240 Gbps and a launch power of 12 dBm, the single-channel PRC with 3 hidden layers raises the Q factor by as high as 0.58 dB, while the dual-channel PRC with 2 hidden layers raises the Q factor by 0.55 dB. In addition, we prove that the deep PRC is able to equalize 16-QAM signals of different launch powers and transmission distances.
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All authors Yi-Wei Shen, Rui-Qian Li, Zheng-Can Sun, Xing Li, Xinyu Liu, Shanshan Yu, Cheng Wang
Optics
Machine Learning-Assisted Analysis and Inverse Design of Prism-Based Surface Plasmon Resonance Sensors
R. Runthala, S. Murai and P. Arora
In this work, we demonstrate a data-driven machine learning (ML) framework for the efficient design and optimization of Kretschmann-configuration-based surface plasmon resonance (SPR) sensors. A physics-based
dataset was generated using a MATLAB-based transfer
matrix method (TMM), covering diverse material properties, layer thicknesses, and multilayer configurations. Optical properties and layer thicknesses were used as input features, while figure of merit (FOM) and minimum reflectance (Rmin) were the target performance parameters. Four ML models, namely CatBoost, XGBoost, LightGBM, and multilayer perceptron (MLP), were benchmarked using R2, mean absolute error (MAE), and root mean squared error (RMSE). The framework integrates ML benchmarking, SHAP explainability, robustness analysis, and optimization-driven inverse design. SHAP-weighted perturbation experiments assessed the model's robustness to input variations. Four optimization
algorithms were employed for inverse sensor design, followed by an analysis of parameter recovery and performance. The optimizers were also evaluated using an independent forward-design task, in which repeated runs converged on a common configuration. The optimized designs agreed closely with direct TMM calculations, with FOM errors of 0.6-0.9 percent and Rmin errors below 0.7 percent. The ML models achieved R2 values greater than 0.99 while reducing computational cost from seconds to milliseconds, corresponding to an acceleration of approximately 10^3 to 10^4 times compared with direct TMM simulations. Overall, the results demonstrate that physics-based surrogate ML models combined with explainability and optimization provide a computationally efficient and interpretable framework for rapid SPR sensor analysis, inverse design, and optimization.
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Optics
Spectral design of confining optical structures by supersymmetry techniques
Samantha Cervantes-Neri, Zulema Gress-Mendoza, Daniel O-Campa et al. (+2 more)
In this work, we apply supersymmetric transformations to an optical medium with quadratic index distributions on both transversal coordinates defining an elliptic profile. In particular, we implement first- and second-order transformations to construct new multi-parametric gradient index patterns that may host one or two subsidiary guided modes with a wide range of spectral properties and transversal intensity and phase distributions. These transformations may be continued up to an arbitrary order enabling the possibility to control the spectral and propagation properties of light beams.
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All authors Samantha Cervantes-Neri, Zulema Gress-Mendoza, Daniel O-Campa, Erik Díaz-Bautista, Sara Cruz y Cruz
Optics
Inductively Scalable, Single-Step Neural Surrogates for Wave-Scattering Inverse Problems
Charles Dove and Laura Waller
Neural network surrogates are an emerging alternative to traditional electromagnetic wave simulators like finite-difference time-domain (FDTD); their goal is to replace rigorous physical simulations with pre-trained neural networks that solve wave-scattering forward and inverse problems orders of magnitude faster. However, nonrecurrent, single-step surrogates have scaled only to a few tens of simulation variables. Here, we show that this barrier can be overcome by dynamically generating salient training examples during training, rather than randomly sampling the large space of possible examples. We introduce an
algorithm that runs in parallel with surrogate training, using gradient ascent to search refractive-index and source configurations for cases where the surrogate disagrees with a full-wave ground-truth simulator. We also use source and ground-truth normalization with an evolving replay
dataset to stabilize and accelerate learning. Using this approach, we train a fast, single-step surrogate for two-dimensional wave scattering with up to 41,772 controllable variables, including dense, freely configurable grids of refractive indices and complex-valued sources. The resulting neural surrogate is robustly accurate across diverse structured and unstructured examples and generalizes inductively to larger domains, reaching over 3 million controllable variables without retraining, a $73.8\times$ increase. We demonstrate the surrogate on large-scale forward simulations and inverse design of freeform beam splitters and gradient-index (GRIN) lenses up to 98 wavelengths wide, showing comparable or better performance than FDTD-based designs, with speedups from $1.29\times$ to $26.5\times$. These results demonstrate a practical path toward fast, robustly accurate, inductively scalable neural simulators for photonic inverse design and other wave-scattering inverse problems.
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Optics · Cross-listed from physics.chem-ph
Temporally Distinguishing Photocatalytic Dynamics
Catherine J. Fabiano, Shan Deneen, Yigao Yuan et al. (+4 more)
Light can induce both photothermal and nonthermal catalytic activity in plasmonic nanoparticles, but the extent, timescale, and efficacy of these two mechanisms remain unresolved. Here we introduce pump-pump photocatalysis, an adaptation of ultrafast excitation correlation spectroscopy in which incident
laser pulses are split into two spatially and energetically equivalent pulses separated by a variable time delay. For a given reaction and catalyst, time-sensitive nonlinear enhancements in photocatalytic activity may be distinguished from time-insensitive responses as a function of time delay, pulse power, excitation wavelength, applied temperature, reactant pressure, and pulse asymmetry. In this way, the timescales of photothermal and nonthermal activity of any photocatalyst may be monitored on sub picosecond to nanosecond timescales, and the conditions for optimal chemical reactivity may be discovered. Here we report ultrafast measurements of the ammonia decomposition reaction using a Cu-Ru
antenna-reactor photocatalyst. Photothermal contributions exhibit little sensitivity to pulse delay, while nonthermal contributions are most apparent at low excitation intensity, moderate temperatures, and sub-nanosecond timescales. Here, nonlinear, nonthermal mechanisms enhance H$_2$ production by a factor up to eleven compared to when pulses overlap. This technique may be used to provide unprecedented in operando diagnostics and control of any photocatalyst for any chemical reaction. Most importantly, these measurements allow us to ascertain the optimal distribution of light to maximize photocatalytic activity.
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All authors Catherine J. Fabiano, Shan Deneen, Yigao Yuan, Luke Kay, Peter Nordlander, Naomi J. Halas, Henry O. Everitt
Optics
Nanophotonic dispersion engineering in tantala-based microresonators with ultralow-loss claddings
Alexa R. Carollo, Atasi Dan, Jizhao Zang et al. (+3 more)
Integrated photonics optimized to leverage low loss, nonlinear-optical processes and optoelectronic integration requires robust optical cladding materials and associated fabrication process flows. We develop low-loss silicon dioxide (SiO$_2$) claddings with tantalum pentoxide (Ta$_2$O$_5$, tantala) integrated photonics to realize robust, high intrinsic quality factor ($Q_i$) microresonators and photonic-
crystal resonators (PhCRs) for
soliton microcomb generation. Specifically, we introduce a full-wafer, low-temperature process compatible with two tantala-based films: pure tantala and an amorphous metal-oxide mixture of titanium dioxide (TiO$_2$, titania) and tantala. Combining tantala with titania enhances the film's resistance to damage from the SiO$_2$ cladding deposition process, offering access to high $Q_i$ above $4 \times 10^6$ in fully cladded microresonators. Our platform supports low-loss edge couplers, group-velocity dispersion engineering by waveguide geometry, access to nanophotonic structures particularly to control phase-matching, and high dimensional tolerance in devices across an entire wafer. Using the platform, we explore the generation of high-efficiency, dark-
soliton microcombs with repetition frequency from 50 GHz to 500 GHz, which supports applications such as photonic artificial intelligence acceleration, electronic signaling, and optical data communication.
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All authors Alexa R. Carollo, Atasi Dan, Jizhao Zang, Haixin Liu, Nitesh Chauhan, Scott B. Papp