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Physics Physics Optics

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Wednesday 2 September

Optics

Laser-induced phase shift of swift electrons

Christian Dwyer and David M. Paganin

We revisit the calculation of the phase shift experienced by swift electrons on passing through the electromagnetic field of a laser. Such phase shifts are now utilized in the form of `laser phase plates' in transmission electron microscopes (TEMs), for example. We calculate the phase shift using three different methods, namely, perturbation theory applied to the Dirac equation, the Volkov solution to the Klein-Gordon equation, and the relativistic Hamilton-Jacobi equation. We find that all three methods are in agreement, and that the calculated phase shift is independent of the relative orientation of the electron and laser beams. The agreement between the quantum and classical theories is explained. The duality between the phase shifts experienced by electrons, photons and neutrons is described. Our Lorentz invariant result for the phase shift differs from certain results published in the literature.
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Optics

Rydberg-atom microwave angle-of-arrival detection via cylindrical vapor-cell-mediated field redistribution

Peicheng Liu, Xingchen Hu, Yong Gao et al. (+3 more)

Microwave angle-of-arrival(AoA) measurement is essential for radar, communication, and spectrum mon-itoring. Existing Rydberg-atom-based AoA schemes employ phase-difference measurements with local oscil-lators, standing-wave fluorescence imaging, or amplitude-ratio readout with internal metal reflectors. Here we demonstrate a new approach: a cylindrical glass vapor cell serving directly as an angle-encoding dielectric structure, eliminating the need for multiple apertures, local oscillators, or imaging optics. The cylindrical geometry produces angle-dependent reflection and field redistribution, mapping the incident AoA onto the effective microwave field sampled by the Rydberg ensemble. This effective field is read out optically via the Autler-Townes(A-T) splitting in the electromagnetically induced transparency(EIT) spectrum. Full-wave simulations and experiments at 11.64 GHz confirm a deterministic, geometry-mediated response over 0{\deg}-90{\deg}.Over the monotonic operating range(55{\deg}-125{\deg}), the angular resolution(minimum distinguishable increment)is 0.05{\deg}, and the angular accuracy(RMSE of repeated measurements) is 0.13{\deg} across the full range, improving to 0.05{\deg} in the optimal region(65{\deg}-115{\deg}). Occupying a sensing volume of~2.5 cm3, this method offers a compact, single-sensor pathway toward Rydberg AoA receivers.
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All authors Peicheng Liu, Xingchen Hu, Yong Gao, Ao-Lin Guo, Yuan Ren, Hao Wu

Optics · Cross-listed from astro-ph.IM

Scalability in Simulating a Large-Aperture, Fresnel Zone Plate Lens for a Conceptual Space Telescope

Maneesha Dushmantha De Zoysa, Yangwoo Seong, Ho Xuan Vinh et al. (+2 more)

As ambitious space telescope concepts such as ultra-lightweight planar diffractive optical elements (DOEs) emerge, validating the performance remains a major computational challenge. Conventional Fourier propagation algorithms were observed to fail at meter-class apertures due to severe memory limits caused by rigid grid-sampling requirements, and the scaled-down proxy models used for reflector telescopes cannot be applied, since scaling compresses the outermost zones that govern resolution. We benchmarked five Fourier-based propagators against a common Fresnel diffraction integral and found that only those decoupling the focal-plane grid from the input aperture converge within a 1% error threshold. With these findings, we implemented an optimized, stripe-processed Chirp Z-Transform (CZT) framework, evaluating the focal spot strictly within a fixed region of interest to reduce peak memory usage. Applied to five full-aperture configurations from 1.0 m to 5.0 m at f/# = 5, the framework predicted spatial resolution and diffraction efficiency to within 0.001% and 0.16% of analytical references, with modulation transfer function results cross-checked by two analytical extraction methods, all within 6.4 GB of memory on a single consumer-grade GPU. This simulation study represents first steps toward quantifying the expected results of ambitious space telescope concepts and aids the mission development (or selection) phase. With a highly accurate, memory-efficient validation tool, the findings obtained will be used to guide the fabrication decisions of future hardware, optical testing, and physical deployment mechanisms of large-scale diffractive telescopes.
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All authors Maneesha Dushmantha De Zoysa, Yangwoo Seong, Ho Xuan Vinh, Jae Hung Han, Hyun Jung Kim

Optics · Cross-listed from physics.med-ph

Mesoscopic Light Localization and Inverse Participation Ratio Analysis of Tissue Structural Disorder for Optical Cancer Detection

Santanu Maity, Mousa Alrubayan and Prabhakar Pradhan

We introduce a mesoscopic physics-based framework that transforms conventional transmission optical micrographs into quantitative maps of tissue structural heterogeneity using the Inverse Participation Ratio (IPR). For the first time, to our knowledge, IPR-based light-localization analysis is applied to cancer tissue imaging to quantify nano- to submicron-scale structural alterations through spatial fluctuations in tissue mass density or refractive index. Unlike conventional morphology-based assessment, this physics-driven approach provides objective structural biomarkers from label-free or routinely stained tissue images. The method establishes a scalable, reproducible platform for quantitative computational pathology and enhanced cancer diagnosis by integrating mesoscopic optical physics with standard optical microscopy.
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Tuesday 1 September

Optics

Optical air waveguides in strong turbulence

A. Goffin, G.I. Babić and H.M. Milchberg

Filament-generated air waveguides offer a route to low loss long-distance optical transport, but their viability in atmospheric turbulence has remained uncertain. Here, we demonstrate with experiments and simulations that guided beams in air waveguides can overcome prior estimated turbulence limits by orders of magnitude in the refractive index structure parameter C_n^2; turbulent index fluctuations much larger than the waveguide index contrast average out along the propagation path. Instead, turbulence imposes two distinct limits: scattering of the guided field beyond the waveguide acceptance aperture and, more importantly at atmospheric strengths, scintillation of the waveguide-forming beam. Scaling of experimentally validated models indicates that filament-generated air waveguides remain viable over kilometer-scale paths under strong near-ground turbulence. Our results establish turbulence limits for long-range optical guiding in the atmosphere.
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Optics

Reciprocal asymmetric transmission in self-shadowed metallized gratings

Can Yesilyurt

A single oblique metallization step gives conventional gratings one-sided silver decoration, established by electron microscopy and elemental mapping. Opposite-face reversal measurements yield finite-aperture red/green/blue transmission ratios up to 1.74 for a 1-$\mu$m grating and 1.5-1.8 for a 30-$\mu$m grating, with reference-normalized transmittances for the latter. Flat-side coating and reduced silver dose give ratios near unity. Maxwell calculations on self-shadowed growth profiles reproduce the directional sign qualitatively and attribute the contrast to diffraction-channel redistribution. The structure remains reciprocal, including its normal-incidence zeroth-order transmission. These results establish directional metallization as a route to direction-selective optical transmission without multilayer alignment or overlay lithography.
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Optics

Multidimensional Double Refraction Microscopy

Jörg König and Christian Cierpka

Multidimensional optical microscopy - extracting 3D location, orientation, and spectral information from nanoscale emitters - is key to modern nanoscience. However, this multidimensional capability requires complex instrumental setups, demanding exceptional stability and specialized expertise in optics. Here, we overcome these barriers by introducing Double Refraction Microscopy (DRM), a passive imaging method providing a straightforward pathway to multidimensional super-resolution imaging. Based on bifocal imaging via a birefringent microscope slide, DRM splits nanoprobe light into a characteristic double image encoding 3D location, orientation, and spectral signature, while requiring zero hardware modifications to standard wide-field microscopes. To showcase its robustness, we implement DRM across three distinct slides of varying materials and thicknesses, calibrating 3D localization with 450-nm nanoparticles and demonstrating high orientation sensitivity using polarization-controlled emitters. Furthermore, we confirm spectral readout using a pinhole array acting as a grid of point emitters back-illuminated at various wavelengths to generate distinct spectral signatures. Finally, we showcase practical utility by performing a two-colour 3D localization measurement within a $10\,\mu\text{m}$ gap, utilizing the single optical pathway of a standard epi-fluorescence microscope. Ultimately, DRM provides the missing optical hardware simplicity to complement established computational tools, promising to transfer advanced super-resolution capabilities from specialized facilities to every laboratory bench.
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Optics · Cross-listed from cond-mat.mtrl-sci

First-principles optical response of shock-compressed LiF: Quasiparticle, excitonic, and ionic-temperature effects

M.S. Fadeev

We investigate the refractive index $n$ of LiF using DFT+G$_0$W$_0$+BSE, with ionic-temperature effects included through QMD. We calculate photon-energy dispersions $n(\omega)$ and $k(\omega)$ at ambient pressure and $n(\rho,T)$ at 532 and 1550 nm under shock compression, where $\rho$ and $T$ vary together. Quasiparticle band structures at ambient and compressed conditions and the ambient-pressure orbital-projected density of states connect the optical response to the electronic structure. At ambient pressure, G$_0$W$_0$ yields a quasiparticle gap of 14.25 eV, close to the experimental 14.2 eV, while BSE reproduces the main excitonic feature at 12.5 eV, close to the observed 12.6 eV. Quasiparticle and excitonic effects are thus essential for accurate optical dispersion; the hybrid HSE functional does not reproduce the optical spectra. Along the principal Hugoniot up to 140 GPa, $n(\rho)$ agrees closely with shock data at 1550 nm and acceptably at 532 nm, and agrees better overall than earlier first-principles calculations. Above approximately 110-120 GPa, QMD produces a downturn relative to cold $n(\rho)$ curves, suggesting that ionic dynamics may contribute to deviations from the linear $n$-$\rho$ Gladstone-Dale relation. QMD-sampling and finite-k-grid uncertainties are estimated, and transition-peak broadening is assessed using a recently proposed criterion. The gap increases under pressure, with a transition to a $\Gamma\to\mathrm L$ indirect gap near 50 GPa. An exploratory calculation at approximately 1400 GPa finds a gap of about 24 eV, disfavoring gap-closure metallization. Structural and elastic benchmarks of the underlying models are also provided.
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Optics

Shot-noise-limited few-cycle mid-infrared frequency comb with attosecond phase stability

Maciej Kowalczyk, Jakub Jaworski, Michał Pietrzak et al. (+5 more)

Achieving sub-cycle waveform control with attosecond-level precision while reaching shot-noise-limited amplitude stability in the mid-infrared spectral range remains a central challenge for ultrafast and precision optical science. Here, we demonstrate a fully stabilized, ultra-stable optical frequency comb (OFC) based on a Kerr-lens mode-locked Cr:ZnS laser operating at 2.3 $\mu$m. The oscillator delivers 40 fs pulses at a 25 MHz repetition rate, which are spectrally broadened to cover two octaves and compressed to a 1.4-cycle, 11 fs duration. Pumped by a custom low-noise erbium-doped fiber amplifier, the laser exhibits an integrated relative intensity noise (RIN) of 0.0026% over 10 Hz–1 MHz, while the noise of the few-cycle output is further suppressed to 0.0017% and reaches the shot-noise limit for Fourier frequencies above 5 kHz. It represents the lowest amplitude noise reported to date for any mode-locked laser. This unprecedented amplitude stability enables carrier-envelope phase (CEP) stabilization with a residual integrated phase noise of only 1.5 mrad (10 Hz–12.5 MHz), corresponding to a CEP jitter of 1.8 as, the highest phase stability for any laser system ever reported. The long-term performance of the fully stabilized OFC is measured over 24 hours, with a power stability of 0.01% and a residual CEP noise of 17 mrad. By combining few-cycle mid-infrared pulses with shot-noise-limited intensity noise and attosecond-level phase stability, the reported OFC provides access to new regimes of quantum-limited metrology and control of ultrafast light-matter interactions.
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All authors Maciej Kowalczyk, Jakub Jaworski, Michał Pietrzak, Karolina Suliga, Paweł Szczypkowski, Paweł Kaczmarek, Alexander Weigel, Jarosław Sotor

Optics

Exceptional Points in Photonics: From Non-Hermitian Physics to Applications

Fan Zhang, Nikolay Solodovchenko, Dmitrii N. Maksimov et al. (+5 more)

Open photonic systems provide a versatile platform for non-Hermitian physics, enabling control over complex spectra, transport, and light-matter interactions. Exceptional points (EPs), at which eigenvalues and eigenvectors coalesce and the governing operator becomes defective, play a central role because they combine branch-point spectral topology, nonanalytic perturbative response, and controllable eigenstate conversion. This Review provides a unified framework for EP photonics by systematically distinguishing exceptional degeneracies according to the underlying operator, spectral variable, boundary conditions, and experimentally accessible observables. We discuss Hamiltonian EPs, absorbing EPs associated with scattering zeros, real-frequency scattering-matrix and Jones-matrix EPs, Bloch and Floquet EPs, and Liouvillian EPs in open quantum systems. We review their spectral topology, static and dynamical encircling, higher-order exceptional structures, and coexistence with bound states in the continuum, together with applications in sensing, lasing, coherent absorption, directional scattering, polarization and wavefront control, nonlinear optics, optical storage, nonreciprocal photonics, and quantum photonics. We also critically assess the current limitations, practical challenges, and future perspectives of EP-based photonic technologies, with particular attention to robustness, noise, scalability, and experimentally measurable performance.
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All authors Fan Zhang, Nikolay Solodovchenko, Dmitrii N. Maksimov, Xuchen Wang, Mingzhao Song, Filippo Capolino, C. T. Chan, Andrey Bogdanov

Optics

Low-threshold vortex lasing in three-dimensional cavities via flatband bound states in the continuum

Zi-Xin Zhou, Weimin Wang, Huijie Li et al. (+2 more)

Bound states in the continuum (BICs) offer a robust route toward high-Q resonators and topological structured-light generation. While optically pumped BIC lasers have advanced significantly, realizing electrically pumped vortex lasers remains challenging due to conflicting requirements for optical confinement and carrier injection. Here, we demonstrate an electrically pumped vector vortex laser based on a photonic crystal-guiding layer-distributed Bragg reflector (PC-GL-DBR) heterostructure. The photonic crystal slab precisely tailors the symmetry and dispersion of BIC modes, including a flatband BIC state, while an intermediate guiding layer enables optical mode engineering without directly patterning the multiple-quantum-well active region, preserving efficient carrier injection and strong optical confinement. Under optical pumping, the device achieves single-mode lasing with a Q of 9700, a threshold of 0.129 kW/cm$^2$, and a side-mode suppression ratio of 26 dB. Crucially, room-temperature electrically pumped vortex lasing is achieved with a low turn-on voltage of 1.8 V, a threshold current density of 0.13 kA/cm$^2$, and a cavity Q of 8600, successfully preserving the characteristic vector-vortex emission of the topological BIC state. These results establish a practical route toward electrically driven BIC vortex lasers for integrated structured-light sources and topological photonics.
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All authors Zi-Xin Zhou, Weimin Wang, Huijie Li, Yan-qing Lu, Jun-Long Kou

Optics

Reaching the optical propagation limit in temporal analog computing

Zeki Hayran

A central goal of optical computing is to perform calculations on the timescale of light propagation. Yet many analog photonic solvers require feedback, storage or field build-up before the answer becomes available, introducing additional latency that limits real-time operation. Here we introduce the concept of two-time modulation for temporal analog computing, in which the material response is independently modulated along two temporal directions, allowing the computational operator to be constructed continuously as the waveform propagates. The solution can therefore form during optical transit, without an additional solution-formation timescale. This form of temporal control allows identical copies of a waveform separated only in time to reach entirely different target outputs within a single spatial channel, and enables nonlocal integral-equation solving in a single passage. The resulting framework brings compact, programmable, real-time analog computation within reach for ultrafast optical information processing.
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Optics

Direct laser-written optomechanical double membranes in an optical microcavity

Lukas Tenbrake, Daniel Stachanow, Florian Giefer et al. (+4 more)

Optomechanical membrane-in-the-middle systems that comprise several coupled compliant membranes offer enhanced optomechanical coupling and collective dynamics. Recent realizations were fundamentally restricted to two membranes and to limited structural optimization of the involved membranes due to their intricate fabrication and experimental integration. Here, we present a fiber-based Fabry-Perot microcavity incorporating monolithically integrated double-membrane resonators fabricated by 3D direct laser writing. We realize controllable mechanical mode hybridization of membranes with coupling rates of up to $J_{\mathrm{mech}}/2\pi = 0.16$ MHz, exceeding the mechanical linewidths. We demonstrate enhanced collective optomechanical coupling of the membrane stack's breathing mode, reaching collective coupling strengths of up to $g_{\mathrm{col}}^{(-)}/2\pi \approx 0.1$ MHz. Our transfer-matrix calculations predict further substantial enhancements with realistic reductions of membrane thickness and spacing, and a larger number of membranes. Our results establish direct laser-written membrane arrays as a scalable platform for multimode cavity optomechanics, combining tunable mechanical interactions, enhanced collective optomechanical coupling, and scalability towards larger mechanically coupled resonator systems.
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All authors Lukas Tenbrake, Daniel Stachanow, Florian Giefer, Jana Blechmann, Wolfgang Alt, Sebastian Hofferberth, Hannes Pfeifer

Optics

High-Speed and High-Responsivity Asymmetric Waveguide Photodiode with Low Optical Back-Reflection

Zhijun Zhang, Xuejie Gao, Qiunan Li et al. (+1 more)

We numerically demonstrate an asymmetric corner-reflector uni-traveling-carrier waveguide photodiode (UTC-WGPD) that simultaneously suppresses optical back-reflection and breaks the bandwidth-responsivity trade-off. Off-center beam coupling introduces geometric asymmetry to eliminate retroreflection while maintaining efficient light trapping. 3D optoelectronic simulations reveal that at 1550 nm, a 15-{\mu}m^2 device exhibits a 275-GHz 3-dB bandwidth, 0.68-A/W responsivity (54.5% quantum efficiency), and -29-dB back-reflection, achieving a 150-GHz bandwidth-efficiency product. This design offers a scalable, low-reflection detection scheme for sub-terahertz transceivers and dense photonic integration.
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All authors Zhijun Zhang, Xuejie Gao, Qiunan Li, Xiaoyu Mi

Optics

Design and Physical Constraints of Synthetic-Frequency Photonic Switching Fabrics

Jorge Parra

Electro-optic frequency conversion and synthetic-frequency coupling are established functions in integrated photonic devices. Their role within a multiport switching fabric, however, depends on how simultaneous optical connections share spatial paths, frequency channels, and device controls. Here, we investigate how coherent coupling among frequency modes can be incorporated into photonic switching fabrics and identify the corresponding architectural and physical constraints. We show that synthetic-frequency coupling does not increase the number of simultaneous orthogonal frequency channels when all channels are freely accessible, but can establish connections that are otherwise blocked by fixed input frequencies, channel-continuity requirements, or unavailable output channels. Under the tested conditions, coupling over the first three frequency spacings in an $8\times8$ fabric with eight frequency channels per port achieves 96.1% of the blocking reduction obtained with unrestricted inter-mode coupling. We further show that a separate frequency-only conversion stage cannot replace missing spatial connectivity. A nominal reduction in spatial switching elements instead requires a joint element whose spatial state can be programmed independently for each frequency channel. Finally, we evaluate a thin-film lithium niobate resonator model using reported electro-optic coupling and photon-decay scales within a multistage Mach-Zehnder interferometer switching fabric. These results clarify the architectural role of synthetic-frequency coupling and the device-level requirements for incorporating it into integrated photonic switching fabrics.
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Optics · Cross-listed from quant-ph

Nonlocal wavefront shaping through complex media

Yanis Trouyet, Neelan Gounden, Pedro Ornelas et al. (+3 more)

Wavefront shaping is a key technique for mitigating scattering in complex media, enabling advanced imaging and optical communication. Yet existing approaches are inherently local, requiring active correction elements - such as spatial light modulators or deformable mirrors - to lie directly in the optical path of the scattered light, which limits their integration into compact imaging systems. Here, we experimentally demonstrate nonlocal wavefront shaping using spatially entangled photon pairs. By applying a phase correction to a photon that never interacts with the scattering medium, we compensate for the distortions experienced by its entangled partner and restore their initial spatial correlations. Our approach physically decouples the wavefront correction from the scattering medium, paving the way for imaging through complex media in compact and otherwise inaccessible systems.
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All authors Yanis Trouyet, Neelan Gounden, Pedro Ornelas, Patrick Cameron, Andrew Forbes, Hugo Defienne

Optics

Topological charge switching in trapped polariton condensates

Jaewon Kim, Hyun Gyu Song, Daegwang Choi et al. (+1 more)

Topological charges in photonic systems provide a robust degree of freedom with direct applications in optical information processing. Bound states in the continuum (BICs) in photonic crystal slabs inherently carry such quantized topological charges, yet they are topologically protected, making active reconfiguration fundamentally challenging. Here, we demonstrate topological charge switching in trapped BIC polariton condensates in a photonic crystal, where spatial modulation of the photonic crystals supports multiple confined states, each carrying a distinct charge. Trapped condensates within the Dirac bandgap are expelled into the leaky band via polariton blueshift, enabling single-mode selection by solely tuning the excitation power. This work offers a platform for optically controlling topological charges by harnessing polariton nonlinearity.
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All authors Jaewon Kim, Hyun Gyu Song, Daegwang Choi, Yong-Hoon Cho

Optics · Cross-listed from nlin.CG

Optical free space extreme learning machine for the implementation of emergent complex systems

Elena Moreno, Fernando Soldevila and Daniel Torrent

Cellular automata conform a set of computational models which evolve with a reduced set of simple rules, yet still are able to show extremely complex emergent phenomena such as fractals and universal computation. Despite their apparent simplicity, they have shown great potential in simulating natural systems and solving challenging computational tasks such as classification and image generation. Instead of implementing cellular automata purely at the software level, it is desirable to design novel analog computing platforms that physically evolve following the automata's underlying rules, thereby reducing power requirements and latency. Here, we introduce an optical extreme learning machine for the simulation of a wide range of cellular automata. Our system operates in free space, and uses a spatial light modulator to encode the evolution rules of the system, while coherent wave propagation performs the corresponding computations. Our results demonstrate a simple, fully-programmable, cost and power efficient, and easy to build and align platform for the implementation of a wide range of complex computational systems such as elementary cellular automata, Conway's Game of Life, and two-dimensional Turing machines.
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Optics

Direct Optimization of a 3D Finite-Source Reflector via Neural-Network Parameterization

Roel Hacking, Lisa Kusch, Martijn Anthonissen et al. (+1 more)

We present a direct optimization method for three-dimensional freeform reflectors that transform the light of a finite-étendue source into a prescribed far-field angular intensity distribution. The reflector profile is represented by a small neural network (a multilayer perceptron), which is trained end-to-end through a differentiable ray-tracing objective. We furthermore parameterize the emission directions in gnomonic coordinates, and show how we use this to ensure that every emitted ray intersects the reflector. At each iteration, the network is converted to a bicubic spline representation for ray-tracing efficiency, and intersections with this smooth surface are solved by a damped Newton solve, with gradients computed via the implicit function theorem. The traced output distribution is compared with the desired target on a 'soft' histogram, under an $H^{-1}$-type spectral weighting that emphasizes long-range transport of flux to improve convergence. Optimization is performed using a BFGS method with self-scaled Broyden updates and a plateau-perturbation rule to prevent stalling. The method converges reliably within seconds on a single GPU for all examples tested.
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All authors Roel Hacking, Lisa Kusch, Martijn Anthonissen, Wilbert IJzerman

Optics

Spatio-temporal coherent molding and retrieval of pulsed signals in optical waveguides

Nika Durishvili, Ramaz Khomeriki, Vakhtang Jandieri et al. (+3 more)

Optical waveguides are key elements for high fidelity, long distance optical communications. Coupled waveguide arrays allow for higher information density, steerting the propagation direction, and for encoding information. However, due to the mixing of relative phases for short pulses containing multiple waveguide-mode frequencies, a process for retrieving an encoded input state once these signals undergo coherent propagation remains elusive. A concept is presented to extract with high fidelity the phase-encrypted input signal from spatio-temporal propagated states. As a realization, an array of coupled waveguides is suggested with the retrieval mechanism being realized by local phase shifts that comply with the identified retrieval concept. Three dimensional full-wave electromagnetic simulations for broadband optical signals in coupled dielectric waveguides confirm the validity of the scheme and the high fidelity of information retrieval pointing to potential applications, for instance in ultrafast coherent coding and decoding of information imprinted on pulse sequences.
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All authors Nika Durishvili, Ramaz Khomeriki, Vakhtang Jandieri, Douglas H. Werner, Daniel Erni, Jamal Berakdar

Optics

Photonic magnetism and altermagnetism without magnetic materials

Tiancheng Zhang, Lijie Li, Zhuo Liu et al. (+7 more)

Magnetism, a fundamental property of solids arising from the collective alignment of electronic spins of magnetic atoms, has recently been expanded by the discovery of altermagnetism, a symmetry-driven phase distinct from both ferromagnetism and antiferromagnetism. Initial efforts to emulate altermagnetism in photonic systems are also being pursued, primarily through the magneto-optic response of materials; however, their intrinsic frequency limitations pose challenges for extending photonic altermagnetism into the optical regime, thereby restricting their material choices and optical applications. Here, we establish a microscopic framework of photonic magnetism through group theory symmetry analysis, defining photonic counterparts of electron spin and magnetic atoms. This approach enables the realization of photonic ferromagnetic, antiferromagnetic, and altermagnetic phases within structured optical lattices constructed by purely dielectric, nonmagnetic materials, which not only broadens the photonic magnetism concept, but also lifts the material and frequency limitations. Analytical models, numerical simulations, and experimental measurements reveal spin-momentum locking directly corresponding to their electronic analogs, showing d-, g-, and i-wave circular dichroism (CD) splitting bands at telecom wavelengths (around 1550 nm). These results demonstrate that altermagnetic order, and magnetism more broadly, can be reconstructed in photonic systems through symmetry and mode coupling alone, opening a new route towards spin-dependent light control and bosonic analogs of quantum magnetic phenomena in dielectric photonic crystals.
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All authors Tiancheng Zhang, Lijie Li, Zhuo Liu, Li Lei, Yi Li, Fanhao Meng, Changhao Ding, Moses C. Hong, Scott Dhuey, Jie Yao

Optics

Dual-polarized, mid-infrared nonreciprocal absorption

Simo Pajovic, Yiting Zhao, Yae-Chan Lim et al. (+2 more)

The emission and absorption of thermal radiation are usually coupled via Kirchhoff's law or reciprocity, stated as the equality of spectral directional emissivity and absorptivity. Magneto-optical materials have recently been identified as a promising route to lifting the constraint of reciprocity, with multiple experimental demonstrations using doped InAs. However, these demonstrations have been limited to p-polarized light in the Voigt configuration, whereas thermal radiation from a blackbody is unpolarized. Therefore, to break reciprocity in both polarization channels, we design a nanophotonic, dual-polarized nonreciprocal absorber operating in the mid-infrared spectral range (11-20 $\unicode{x03BC}$m), consisting of an a-Si photonic crystal slab on top of a doped InAs substrate described by an antisymmetric, nonreciprocal dielectric tensor under an applied magnetic field. The photonic crystal slab supports eigenmodes that couple to both s- and p-polarized light, resulting in absorption peaks that frequency shift in opposite directions for forward- and backward-propagating light$\unicode{x2014}$a signature of nonreciprocity in planar, subwavelength systems. We fabricate our design, then measure its room-temperature absorptance using magnetic-field-integrated absorptance spectroscopy, experimentally demonstrating nonreciprocal absorption for both polarizations. Our design is a step toward the complete control of light as heat, which could improve photonic energy conversion, thermal management, and mid-infrared optical isolation and circulation.
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All authors Simo Pajovic, Yiting Zhao, Yae-Chan Lim, Ruzan Sokhoyan, Harry A. Atwater

Monday 31 August

Optics

Strong suppression of the photonic density of states in three-dimensional disordered silicon networks

Abraham Aguilar Uribe, Francisco Hernández Alejandre, Mattis Reisner et al. (+4 more)

Photonic bandgaps can open not only in crystalline dielectric materials but also in amorphous structures. Self-uniform amorphous gyroid networks have been proposed as promising disordered photonic architectures. Motivated by numerical studies, we combine direct laser-writing lithography with advanced materials processing to fabricate these structures from high-refractive-index silicon. Spectroscopic measurements at mid-infrared wavelengths reveal pronounced transmission minima. To investigate the formation of photonic band gaps in amorphous structures, we develop polarization-resolved transmission spectroscopy that separates ballistic and multiply scattered contributions, enabling direct identification of the underlying transport regimes. We observe a strong suppression of diffuse transmission, providing direct experimental evidence for a breakdown of conventional diffuse transport associated with a strongly reduced photonic density of states. Together with large-scale numerical simulations, our results establish the presence of a deep photonic pseudogap in an amorphous three-dimensional dielectric material and open new opportunities for observing disorder-induced localization phenomena, including Anderson localization of light.
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All authors Abraham Aguilar Uribe, Francisco Hernández Alejandre, Mattis Reisner, Geoffroy Aubry, Luis S. Froufe-Pérez, Marian Florescu, Frank Scheffold

Optics

Modeling and Optimization of Cascaded Four-Wave Mixing toward the VUV in Xenon-Filled Negative-Curvature Fibers

Jose Otavio Rosa, Frédéric Gérôme, Fetah Benabid et al. (+2 more)

In this work, we thoroughly characterize third- and fourth-harmonic generation through cascaded four-wave mixing in a xenon-filled negative-curvature hollow-core fiber operated under a pressure gradient. The experimental results are supported by both a semi-analytical model and numerical simulations, which accurately reproduce the pressure dependence of the harmonic conversion. We identify the optimum pressure conditions for third and fourth-harmonic generation and experimentally observe the cascaded four-wave-mixing process extending into the vacuum ultraviolet (VUV), up to the sixth harmonic at 172 nm, with the accessible spectral range limited by the available VUV filter.
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All authors Jose Otavio Rosa, Frédéric Gérôme, Fetah Benabid, Jonas H. Osório, Jonathas de Paula Siqueira

Optics · Cross-listed from physics.atom-ph

Collective dressed states for inelastic light scattering by atomic ensembles

Sébastien Lucas, David Wilkowski, Christian Miniatura et al. (+1 more)

We develop a general dressed-state framework for computing fluorescence spectra, probe absorption spectra, and photon-photon correlations of light scattered by ensembles of $N_\mathrm{at}$ two-level atoms with arbitrary $J_g \to J_e$ transitions driven by intense coherent fields. The approach employs a full vectorial treatment of the electromagnetic field, handles any atomic geometries, illumination directions, and polarizations, and yields optical observables as explicit sums of Lorentzian lines whose positions, widths, and weights are directly tied to the eigenvalues and eigenvectors of the Lindbladian. The framework is implemented in an open-source Python package and benchmarked against exact single- and two-atom calculations. We identify geometries in which the full vectorial description is essential, and the scalar approximation fails qualitatively. Applying the method to pairs of atoms with a $J_g=0\to J_e=1$ transition, we show that elastic and inelastic scattered intensities collapse onto universal master curves controlled by a single collective saturation parameter built from the dominant superradiant mode, across several orders of magnitude in drive strength and interatomic distance. We identify collective phenomena that require a description beyond this single-mode picture. Extending the analysis to atoms with ground-state degeneracy, we find that most collective features carry over, while two qualitatively new effects emerge: an incoherent spontaneous Raman channel that modifies the scaling of inelastic emission, and a slow timescale in the time-delayed correlations $g^{(2)}(\tau)$ governed by the competition between Raman scattering and subradiant decay, controlled by a single dimensionless parameter. These results provide both physical insight and practical computational tools for engineering collective optical responses in few-atom systems such as optical tweezer arrays.
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All authors Sébastien Lucas, David Wilkowski, Christian Miniatura, Sergey E. Skipetrov

Optics · Cross-listed from hep-ph

Searching for Axions on a Higher Note: Third-Harmonic Generation from Colliding High-Intensity Laser Beams

Ashis Paul, Leone di Mauro Villari, Davide Tedeschi et al. (+3 more)

We propose a new laboratory strategy to generate and detect axion-like particles via third-harmonic generation induced by two non-collinear, polarised high-intensity laser beams of peak intensity of the order of $10^{24}\,\mathrm{W/cm^2}$, where the third-harmonic signal is generated by the axion field. Starting from the axion-modified Maxwell equations, we analytically derive the axion-induced third-harmonic field, and show that by using state-of-the-art petawatt laser facilities, a detectable signal can be obtained over a broad range of axion masses and couplings. A key feature of the setup is that the axion-photon conversion rate can be resonantly enhanced by tuning the angle between the two beams through a mechanism that does not depend on the physical volume of the apparatus. The proposed configuration may therefore probe an unexplored region of axion parameter space and pave the way for next-generation high-power laser-based axion searches.
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All authors Ashis Paul, Leone di Mauro Villari, Davide Tedeschi, Carino Ferrante, Luca Di Luzio, Andrea Marini

Optics

Integrated Microwave Photonics: From Material Platforms to Systems-on-Chip

Jiejun Zhang and Jianping Yao

In this paper, recent advances in integrated microwave photonics (IMWP) are reviewed, including material platforms, integration technologies, and system functionalities. Emerging opportunities and future perspectives are discussed. Silicon (Si) and silicon nitride (SiN) provide dense routing, programmable filtering, and low-loss delay; indium phosphide (InP) supplies optical gain, light generation, and high-speed photodetection; thin-film lithium niobate (TFLN) offers linear and broadband electro-optic conversion; and photonic integration is emerging as a practical path to synergize complementary capabilities. Recent work shows a marked shift from isolated modulators, filters, and delay lines toward chip- and module-level systems, ranging from signal processing engines, real-time spectrum sensing, to full-spectrum wireless links, fiber-wireless conversion, silicon beamforming, integrated radar, programmable processors, and photonic convolution engines with on-chip sources and detectors. As these demonstrations become more mature and complete, the key questions move beyond bandwidth and efficiency toward system integration, microwave packaging, calibration stability, analog link performance, and application-level validation.
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Optics

Quantum Dot Colloidosomes as Triggerable Microlasers

Cristian Gonzalez, Saranya Subramanian, Marco Reale et al. (+13 more)

Quantum dot (QD) supraparticle lasers are promising platforms for microscale light sources and photonic labeling, yet their optical properties are set during assembly. Here we introduce QD colloidosomes, liquid-core/solid-shell supraparticles that combine whispering-gallery-mode optical feedback with stimulus-triggered structural collapse. Intact QD colloidosomes show cavity-defined lasing with fluence thresholds of ~2.8 mJ/cm2 and linewidths of 2.2-3.7 nm, demonstrating efficient light trapping without a solid core. We identify shell continuity as a critical determinant for whispering-gallery feedback and lasing by exploring a morphological continuum of suprastructures comprising solid supraparticles, colloidosomes, and microporous hollow shells. Intact colloidosomes support narrow cavity modes, whereas porous shells remain broadband even at high pump fluence. We show that colloidosomes can be driven to rupture and release payload through well-defined pathways, including meniscus-driven capillary failure, uniform heating, and localized near-infrared activation, thereby reconfiguring their optical response from cavity-defined lasing to broadband emission. These results establish QD colloidosomes as reconfigurable microlasers that couple optical-state switching and triggered release within a single self-assembled platform.
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All authors Cristian Gonzalez, Saranya Subramanian, Marco Reale, Giuseppe Soligno, Ilia Geints, Siyuan Yin, Claire Y. Kang, Ricky Ronquillo, Gary Chen, Marco Cannas, Cherie R. Kagan, Alice Sciortino, Michael Engel, Fabrizio Messina, Christopher B. Murray, Emanuele Marino

Optics

Dual-Gradient Plasmonic qBIC Metasurface for Time-Resolved In Situ Optimization of Molecular Vibrational Sensing in Water

Tao Jiang, Michael Hirler, Lina Rohrer et al. (+8 more)

Metaphotonic platforms based on quasi-bound states in the continuum (qBICs), harnessing strong near-field enhancement and deeply subwavelength field confinement, provide a versatile framework for surface-enhanced infrared absorption (SEIRA) spectroscopy. However, real-time molecular sensing in water using qBIC metasurfaces remains challenging. First, strong water absorption in the mid-infrared region damps qBICs and obscures weak analyte signals. Second, conventional metasurfaces rely on discrete arrays targeting individual wavelengths and coupling conditions, increasing the device footprint and fabrication effort required to match the qBIC to the molecular vibrational resonance. Here, we present a dual-gradient plasmonic qBIC metasurface with diamond-shaped resonators for in situ molecular vibrational sensing in water, where spatially encoded gradients in the scaling factor and asymmetry parameter independently control the qBIC spectral positions and radiative rates, respectively, across a 1000 um x 700 um footprint. Building on this capability, we experimentally monitor lipid vesicle dynamics in real time and resolve the carbonyl vibrational signature despite the unavoidable water absorption. We then directly identify the optimal sensing condition and track its evolution across the spatially encoded parameter space. The results establish a compact single-chip strategy that combines adsorption-kinetics monitoring, vibrational fingerprint detection, and on-chip optimization, opening opportunities for investigating biological dynamics under aqueous conditions.
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All authors Tao Jiang, Michael Hirler, Lina Rohrer, Martin Barkey, Dmytro Gryb, Leonardo de S. Menezes, Silvia Holler, Stefan A. Maier, Yohan Lee, Alexander A. Antonov, Andreas Tittl

Optics

Towards Site-Selective Fabrication of Near-Infrared Emitters in hBN

Tadas Paulauskas, Vakaris Silys, Edgaras Markauskas et al. (+5 more)

Spatial control of near-infrared (NIR) emission from hexagonal boron nitride (hBN) would facilitate coupling atomic-scale light sources to photonic structures, yet oxygen-related NIR emitters are generally formed at stochastic locations. Here, we combine single-shot femtosecond laser writing with annealing in an oxygen-rich environment to bias NIR activation toward predefined coordinates in exfoliated hBN. Spectra acquired with 532, 635, and 785 nm excitations show narrow and multipeak emission extending to a wavelength of 1 um. Among the spectra collected at written sites, over 83% under 785 nm excitation and 71% under 635 nm excitation contain at least one resolved peak above 810 nm. The emission intensity increases monotonically with writing-pulse energy, suggesting tunability and indicating that the optimum for the single-emitter regime may require lower energies. Band-pass-resolved measurements show zero-delay correlation dips with g2(0) values indicative of single-photon emission but also reveal contributions from the spectral background. Spectrally resolved time series under 785 nm excitation show persistent bands over the recorded intervals as well as intermittent emission above 900 nm. This approach demonstrates NIR-emitter activation at predefined sites while identifying residual off-site activation and spectral multiplicity as the principal targets for further optimization.
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All authors Tadas Paulauskas, Vakaris Silys, Edgaras Markauskas, Julius Janusonis, Ifra Bibi, Skirmantas Kersulis, Danielis Rutkauskas, Marek Maciaszek