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Monday 14 September

Optics

A nonlinear hydrodynamic theory of ultrafast laser self-organization

Jean-Philippe Colombier, Emeric Gandon, Quentin Fornasiero et al. (+1 more)

Ultrashort laser pulses can induce order out of chaos. A femtosecond pulse melts a metal surface for about a hundred picoseconds; under photoexcitation with no net polarization axis, the resolidifying film nonetheless organizes into regular nanoscale patterns. Here we derive from first principles the nonlinear hydrodynamics responsible for it and show it accounts for the full phase diagram of morphologies from measurable laser and material parameters. Starting from the Navier-Stokes equations in the lubrication limit, the molten film obeys a damped Kuramoto-Sivashinsky equation that reduces to a Swift-Hohenberg formalism near threshold, with every coefficient fixed by the laser fluence, melt thickness, optical skin depth, and thermocapillary response. The ratio of melt depth to optical skin depth sets the pattern wavelength, while the inter-pulse delay, via post-pulse damping, gates the route from flat surface to ordered pattern to chaos. We validate the phase diagram (hexagonal cavity arrays, bistable mixed states, labyrinths) numerically and confront it with pulse-resolved experiments on two metals, Ni and Fe3Cr. The agreement between theory and experiment quantitatively links the microscopic laser-material response to the macroscopic pattern selected after many pulses. This order is self-limiting: the same corrugation the instability builds scatters the modes that build it, and simulations, with every scale fixed by material parameters, place the coherence breakdown near a roughness of 30 nm after a few tens of pulses, a finite window confirmed by pulse-by-pulse measurements of orientational order on the experimental surfaces; at stronger coupling, disorder does not destroy the pattern but saturates and pins it instead. This yields a closed, predictive description of laser-driven self-organization, from single-pulse melt dynamics to the arrest of nanoscale order.
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All authors Jean-Philippe Colombier, Emeric Gandon, Quentin Fornasiero, Eduardo Brandao

Optics

Micro-transfer Printed Blue InGaN Lasers on Silicon Nitride Photonic Integrated Circuits

Konstantinos Akritidis, Krzysztof Gibasiewicz, Han Wang et al. (+8 more)

Expanding integrated photonics into the blue spectral range requires high-performance light sources, making the gallium nitride (GaN) material family indispensable. While silicon nitride (SiN) platforms offer a robust, CMOS compatible passive ecosystem for visible wavelengths, seamlessly integrating GaN lasers remains a major bottleneck. Conventional heterogeneous integration methods present distinct trade-offs: full-wafer bonding achieves high throughput but requires careful management of thermal and lattice mismatches across large areas, whereas flip-chip bonding ensures high yield through pretesting but is constrained by sequential processing speed. In this landscape, micro-transfer printing (MTP) emerges as a disruptive, material-efficient alternative, bypassing these limitations by combining high-density parallel integration with known-good-die selection. Applying MTP to GaN, however, presents a significant material challenge: due to its chemical inertness and strong III-N bonds, device release typically relies on electrochemical etching, which can compromise material quality. Here, we overcome this hurdle and demonstrate the first micro-transfer printed blue lasers on a SiN platform. Using a heavily doped n-type sacrificial layer together with optimized electrochemical etching conditions, we release smooth-surfaced thin-film light sources from bulk GaN substrates. Following release, the devices are integrated and butt-coupled to SiN fork-shaped edge couplers, achieving high current densities exceeding 20 kA$/$cm$^2$ alongside lasing at 455 nm. These results expand the visible integrated photonic toolkit and establish a framework for multi-wavelength integration, opening new avenues for next-generation technologies including flow cytometry, quantum computing, optical communications, and augmented/virtual reality.
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All authors Konstantinos Akritidis, Krzysztof Gibasiewicz, Han Wang, Iryna Levchenko, Max Kiewiet, Maximilien Billet, Mikołaj Chlipała, Karolina Peret-Malessa, Pol Van Dorpe, Henryk Turski, Bart Kuyken

Optics

High-efficiency integrated laser on erbium-doped lithium niobate-on-insulator

Chunyu Zhang, Yuqi Zhang, Yiyang Zou et al. (+11 more)

Lithium niobate on insulator (LNOI) combines the outstanding optical properties of lithium niobate (LN) with strong optical confinement, scalable fabrication and high-density integration, making it a leading platform for integrated photonic chips. Recent advances in LNOI photonics have mainly centred on passive and electro-optic components, including couplers, waveguides, microcavities and modulators, whereas efficient on-chip laser sources remain insufficiently developed, limiting the realization of fully integrated LN photonic systems. Because LN is an indirect-bandgap material, lasing on LNOI generally relies on photoluminescence from rare-earth-ion doping, yet the conversion efficiency of doped LNOI lasers has remained low. By comparing LNOI microcavity lasers with fibre lasers and waveguide amplifiers, we identify the limited number of rare-earth ions participating in stimulated emission as a key factor responsible for inefficient pump utilization. Here we demonstrate an integrated Er-doped LNOI laser that combines high-quality, highly Er-doped LN, a large-diameter wide-microring resonator, a low-loss waveguide amplifier and bidirectional pumping. This architecture enables a slope efficiency of 16.91% at 1562 nm, exceeding 10% on the LNOI platform for the first time. Our results provide a route towards high-efficiency LNOI lasers for fully integrated photonic systems.
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All authors Chunyu Zhang, Yuqi Zhang, Yiyang Zou, Xiaomin Wang, Binwen Niu, Cangsu Yuan, Tongxin Xue, Chunlin Zhu, Hongde Liu, Dahuai Zheng, Shiguo Liu, Fang Bo, Yongfa Kong, Jingjun Xu

Optics

Synthetic SU(1,1) Gauge Control of Non-Hermitian Light

Wanyue Xiao, Ruo-Yang Zhang, Yuqiong Cheng et al. (+1 more)

Synthetic gauge fields enable nontrivial light control but remain largely restricted to compact groups such as U(1) and SU(2). Here, we study paraxial light propagation under a noncompact SU(1,1) gauge field realized in a non-Hermitian medium. Under this field, light evolves pseudo-unitarily and conserves pseudo-intensity despite material gain or loss. The gauge field drives Lorentzian precession of the optical pseudospin on a Bloch hyperboloid, producing rotations, boosts, and exceptional-point critical dynamics in an internal Minkowski space. A non-Abelian Lorentz force converts these internal dynamics into real-space oscillatory, hyperbolic, and cubic pseudo-intensity centroid trajectories, even in a uniform medium, while light of opposite pseudo-intensity can drift oppositely-a non-Hermitian spin-Hall-like effect. Our results connect non-Hermitian wave physics with noncompact gauge dynamics and reveal hidden conserved quantities in non-Hermitian light transport.
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All authors Wanyue Xiao, Ruo-Yang Zhang, Yuqiong Cheng, Shubo Wang

Optics

Subwavelength exceptional points in dispersive resonator arrays

Konstantinos Alexopoulos

Exceptional points provide a mechanism for producing strong spectral sensitivity in non-Hermitian wave systems. For subwavelength resonators with highly dispersive material parameters, however, the resonance problem is not a linear eigenvalue problem in the frequency. In this paper, we use the Lippmann-Schwinger formulation and the associated volume-potential reduction to study exceptional points in dispersive resonator arrays. The reduction leads to a finite-dimensional nonlinear matrix pencil whose entries encode both the local material response and the volume-mediated interaction between the resonators. We characterize exceptional points as defective characteristic values of this pencil and derive explicit conditions for dimers and higher-order systems. We show that passive damping and detuning can generate exceptional points without imposed gain, and we formulate an inverse-design condition for placing such degeneracies at prescribed frequencies. We also prove the corresponding Puiseux splitting laws and identify how material dispersion enters the leading sensitivity prefactor. Numerical experiments, including halide-perovskite-inspired dimers and trimers, illustrate the theory and show that the exceptional-point mechanism persists for explicit highly dispersive passive material laws.
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Optics

Enhanced Spin-Orbit Interaction of Light through Complex Fresnel Reflection

Dileep Kumar Upadhyay and Nirmal K. Viswanathan

Spin-orbit interaction (SOI) of light manifests as the generation of a spin-dependent vortex beam and the spin-Hall effect when a spin-polarized beam interacts with an optical interface at normal and oblique incidence, respectively. The weak SOI limits its widespread use for quantifying physical quantities in various applications. We demonstrate a significantly enhanced SOI effect, approaching the strong-coupling regime, by retroreflecting a nonparaxial focused beam of light at a multilayer dielectric mirror. The large difference in angle-of-incidence-dependent Fresnel reflection coefficients (r-TE, r-TM ) introduced by the mirror simultaneously enhances the spin-orbit-converted vortex-beam amplitude and the spin-Hall effect in the reflected beam. Near-field superposition of the orthogonal polarization components in the reflected beam yields a spatially nonuniform beam field with C-, V-, and L- polarization singularities. These topological features are mapped and are used to demonstrate the transverse and 3D spin-Hall effect in the focal region. The superposition of enhanced optical near-fields and the lossless broadband nature of the mirror reflectivity are expected to enable a variety of polarization topologies and to tailor their features via designed mirror reflectivities.
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Optics

Gaussian-splatting ptychography via explicit and interpretable primitives

Qianhao Zhao, Zhixuan Hong, David Brady et al. (+9 more)

Ptychography overcomes the limits of lenses by co-designing optics and computation. Yet prevailing implementations reconstruct on a pixel grid, where weakly-constrained modes drift and recovery demands redundant data. Here we introduce Gaussian-splatting ptychography, representing object and probe as Gaussian primitives. Relocation concentrates primitives where structure is dense, and overlapping primitives couple neighbouring pixels to suppress mode drift. The scheme unexpectedly restores the low-frequency phase that conventional approaches lose, enabling uniform phase transfer across spatial frequencies. The probe is represented and updated in its pupil plane from a random start. In Fourier ptychography, the pupil-plane model recovers severe aberrations where pixel-grid solvers fail. In conventional optical, X-ray and electron ptychography, the pupil-plane primitives also recover the real-space probes with no model of beam-forming optics. The representation cuts memory up to 14-fold and recovers specimens from fewer acquisitions. At electron wavelengths, it resolves atomic structure at tens of electrons per square angstrom.
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All authors Qianhao Zhao, Zhixuan Hong, David Brady, Changhuei Yang, Andrew Maiden, Zhongtian Zheng, Ruihai Wang, Daniel Gage, Mary Lipton, Christopher Anderton, Arunima Bhattacharjee, Guoan Zheng

Optics

Proximal-Only Transmission Matrix Recovery of an Arbitrarily Deformed Graded-Index Multimode Fiber

Cole Reynolds

The multimode fiber is among the thinnest imaging conduits available, carrying hundreds to thousands of spatial modes through a cross-section comparable to a human hair, but its endoscopic capabilities are currently limited by the sensitivity of the transmission matrix to the fiber's deformed state. Proximal-only recovery of the fiber's transmission matrix is an appealing approach for enabling general use multimode fiber endoscopy, and within the last decade, machine learning techniques have been applied to both single-ended and double-ended transmission matrix recovery tasks. We present a new approach to this interdisciplinary problem and show that neural networks can generalize to recover transmission matrices of an arbitrarily deformed graded-index multimode fiber from proximal measurements alone.
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Sunday 13 September

Optics

Sub-kHz linewidth integrated extended-DBR Pockels lasers using lithium tantalate

Hugo Larocque, Zhuoya Yuan, Zihan Li et al. (+7 more)

Tunable low-noise lasers are crucial components employed in modern metrology. Advances in photonic integrated circuit technology have provided a new platform for compact integrated lasers with large output powers, frequency-agile tuning, and narrow linewidths. For instance, lithium niobate extended-DBR lasers can yield output powers in the tens of mW, GHz-level tuning ranges, and tuning rates in the hundreds of MHz. However, noise levels achievable in other integrated laser designs remain challenging to reach. Here, we address this challenge by implementing extended-DBR lasers in lithium tantalate, thereby achieving intrinsic linewidths as low as 24 Hz, output powers of 10 mW, with tuning features on par with those of lithium niobate. The extended-DBR laser is assembled with modern packaging solutions to improve its robustness and demonstrate long-term stability with a free-running frequency drift within a range of 232 MHz over 19 hours. These benefits, in conjunction with lithium tantalate's suitability for volume manufacturing, promise to considerably expand accessibility to a new generation of widely tunable and low-noise integrated lasers.
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All authors Hugo Larocque, Zhuoya Yuan, Zihan Li, Giovanni Scarioni, Annika Schoels, Jiale Sun, Anat Siddharth, Xin Ou, Simone Bianconi, Tobias J. Kippenberg

Optics · Cross-listed from cond-mat.mes-hall

Giant second-harmonic generation in few-atomic layer metals

Alessio Zaccone

Quantum confinement restructures the electronic phase space of ultrathin metals, but the resulting density-of-states (DOS) change is not generically large. We show that, within a three-dimensional confinement theory based on the suppression of long-wavelength electronic states, the Fermi-level DOS enhancement on the weak-confinement branch is bounded by $(4/3)^{1/3}-1\simeq10.1\%$. Instead, confinement-induced redistribution of electronic phase space can be strongly amplified by resonant denominators in the second-order susceptibility. A minimal double-resonance closure predicts giant amplification when the film thickness approaches $L_c=(2\pi/n)^{1/3}$, where $n$ is the carrier density, and a dominant optical pathway lies within a dephasing linewidth of resonance. Applied to recent Ag(111) measurements, the theory gives an effective phase-space carrier density parameter $n_{\rm eff}\simeq3.6\times10^{20}\,\mathrm{cm}^{-3}$, a tenfold enhancement of $|\chi^{(2)}|$, and hence the observed $\sim100$-fold increase of thickness-normalized second-harmonic-generation efficiency, together with the observed non-oscillatory thickness dependence.
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Optics

Chirped Bragg Gratings as Passive Photonic Reservoirs: An Experimental Proof-of-Concept for Temporal Information Processing

Isaac Yorke

Passive photonic structures offer a potential route toward reservoir computing by exploiting intrinsic optical propagation, delay, interference, and memory effects for temporal information processing. This work investigates whether a chirped Bragg grating (CBG) can exhibit fundamental physical properties relevant to a passive photonic reservoir. Rather than presenting the CBG as a complete reservoir computer, the study provides an early proof-of-concept assessment based on experimentally measured device characteristics. Wavelength-dependent group delay and reflection coefficient measurements obtained from a silicon photonic CBG are incorporated into a distributed delay model in which multiple delayed contributions form the reservoir states. The resulting system is examined with respect to distributed delay, fading memory, temporal mixing, and memory capacity using a linear readout based on the standard memory capacity formulation. The results demonstrate that the measured CBG response provides a distributed temporal memory over the experimentally observed delay range and produces temporal mixing through the superposition of multiple delayed contributions. The memory capacity analysis further indicates that past input symbols can be reconstructed from the distributed delay states, providing quantitative evidence of temporal information retention in the measured CBG response. These results suggest that a passive CBG possesses several physical characteristics relevant to reservoir computing and may therefore provide a simple photonic substrate for reservoir-like temporal processing. The study is intended as an initial proof-of-concept, providing a foundation for future experimental and task specific investigations of passive CBG-based photonic reservoirs.
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Optics

Hybrid Nanocone-Nanohole Light Trapping for High-Efficiency Thin-Film Silicon Solar Cells

Nishat Tasnim, Kawshik Nath and Ahmed Zubair

Thin-film silicon solar cells exhibit weak absorption at longer wavelengths of visible light due to their limited optical thickness. To overcome this inherent limitation, a hybrid nanocone-nanohole light-management architecture is proposed by integrating front-surface silicon nanocones with embedded air-filled nanoholes in the absorber layer. The nanocones provide a gradual refractive-index transition that suppresses front-surface reflection, while the nanoholes enhance optical confinement through multiple scattering and internal reflection. The structural parameters are systematically optimized using finite-difference time-domain (FDTD) simulations coupled with electrical device modeling. Under optimized doping conditions and isothermal steady-state operation, the optimized design yields a short-circuit current density of 34.64 mA cm-2, an open-circuit voltage of 0.82 V, a fill factor of 86.27%, and a power conversion efficiency of 24.42%, representing a 17.74% improvement over a comparable nanohole-based design. Furthermore, coupled opto-electro-thermal simulations show that the proposed hybrid nanocone-nanohole structure retains 95.21% of its efficiency under non-isothermal operation up to45 degree celsius, demonstrating excellent thermal stability. These results highlight the potential of the proposed hybrid nanocone-nanohole design as an effective light-management strategy for high-efficiency and thermally robust thin-film silicon solar cells.
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Optics · Cross-listed from cond-mat.mes-hall

Spectral density of angular momentum transfer from a swift electron to a large spherical nanoparticle

Jorge Luis Briseño-Gómez and Alejandro Reyes-Coronado

Swift electrons in scanning transmission electron microscopy transfer both linear and angular momentum to nanoparticles, underlying electron-beam-driven nanoscale manipulation ("electron tweezers"). Prior theory relied either on the small-particle (dipolar) approximation, valid only well below experimentally relevant sizes, or on frequency-integrated multipolar calculations that leave the spectral structure of the interaction unresolved. Here we present a fully retarded, causal, multipole-converged electrodynamical methodology for the angular momentum transfer from a swift electron to an isolated spherical nanoparticle, based on a closed-surface Maxwell stress tensor formulation whose angular integrals reduce analytically to a small, material- and trajectory-independent set of irreducible integrals over associated Legendre functions. This lowers the cost of the double multipolar sum, enabling convergence up to l_max=51 for nanoparticles as large as a=50 nm, nearly four times the order of the largest previous calculation at this size and previously unreached for an optically complex, interband-dominated material. Applied to aluminum and gold nanoparticles up to a=50 nm, the method resolves the transfer spectral density across the full frequency domain, showing it is set by interference between the electron field and the field scattered by the nanoparticle, which dominates the scattered-scattered contribution at essentially every frequency; the electric contribution dominates at moderate speeds, but the magnetic contribution, of the same sign, grows steadily in relative weight with electron speed, from a few percent of the total at v = 0.5c to between a quarter and a half of it at v = 0.95c for trajectories passing close to the nanoparticle surface.
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Optics

Square-shaping of sturdy optical vortex droplets in quasi-phase-matched photonic crystals

Xuening Wang, Yimin Zhang, Qiuyi Ning et al. (+5 more)

We elaborate a scheme for controllable shaping of self-trapped vortex states in a quasi-phase-matched three-dimensional photonic crystal with the combination of self-focusing quadratic and defocusing cubic material nonlinearities. The setting gives rise to sturdy droplet-like vortex modes, capable to adapt to externally imposed strong geometric constraints. The application of a square-shaped modulation in the transverse $\left(x,y\right) $ plane and periodic quasi-phase-matching to the quadratic nonlinear coefficient $d_{z}$ along the propagation direction $z$ leads to the formation of square vortex droplets (VDs) with fourfold rotational symmetry ($C_{4}$). These states preserve the vortical phase circulation and exhibit robust propagation in a broad parameter region. In the oversaturated regime dominated by the cubic self-defocusing, the square-shaped VDs obey the anti-Vakhitov–Kolokolov stability criterion. The results, which are produced, chiefly, for the VDs with topological charge $S=1$, and also, in a partial form, for $S=2$ and $4$, reveal an unexpected universality: the vortex robustness is not contingent upon the circular symmetry. Thus, the combination of the competing nonlinearities and geometric confinement provides not only an effective method for the formation of self-trapped vortex states, but also new insight into generality of the topological protection in nonlinear optical fields.
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All authors Xuening Wang, Yimin Zhang, Qiuyi Ning, Bin Liu, Li Zhang, Hexiang He, Boris A. Malomed, Yongyao Li

Saturday 12 September

Optics · Cross-listed from cond-mat.mtrl-sci

Ultrafast Magnetization Induced from Raman-Active Axial Chiral Phonons

Chuankun Huang, Alexander Milner, Jiaming Luo et al. (+8 more)

Axial chiral phonons, which carry angular momentum and exhibit unusually large magnetic moments, provide a new degree of freedom for controlling the time-reversal symmetry and magnetic properties of quantum materials. While infrared-active axial phonons are efficiently excited to large amplitudes by circularly polarized terahertz pulses, their application may be constrained by short lifetimes, small penetration depths, low spatial resolution, and limited availability of optical sources. Here, we report that an axial Raman-active phonon mode in CeF3 exhibits a significant magnetic moment and an exceedingly long lifetime that more closely matches the paramagnetic spin dynamics. The axial phonon population is resonantly driven by a near-infrared laser pulse with rotating linear polarization, known as an optical centrifuge, a coherent control scheme never applied to solids before. The phonon-driven magnetization observed by time-resolved Faraday rotation scales quadratically with incident power and rapidly decreases at high temperatures, consistent with phonon inverse Faraday effect from many-body spin-phonon coupling. Our findings open a new avenue for using shaped laser pulses from widely accessible light sources to manipulate coherent axial chiral phonons and ultrafast spintronics.
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All authors Chuankun Huang, Alexander Milner, Jiaming Luo, Jianbo Ye, Gaihua Ye, Junjie Zhang, Cynthia Nnokwe, Boris I. Yakobson, Rui He, Valery Milner, Hanyu Zhu

Optics · Cross-listed from quant-ph

Noise-aware derivative feedback of a harmonic oscillator under quantum-limited position measurement

Vedran Vujnović

We study measurement-based feedback control of a damped harmonic oscillator, motivated by optomechanical and interferometric position measurements, in which feedback is synthesized from a displacement measurement. For a band-limited derivative controller, the loop shapes the mechanical susceptibility and reinjects measurement noise, creating a tradeoff between stabilization and noise amplification. We present a compact classical formulation that isolates this tradeoff in the closed-loop displacement spectrum and identifies the parameters governing resonance suppression versus noise-driven actuation. We then extend the same topology to a quantum-limited position detector, enforcing the imprecision-backaction constraint and introducing finite measurement bandwidth that regularizes high-frequency noise reinjection and adds phase lag in the feedback path. In the high-$Q$ regime we obtain an analytic design rule for the optimal feedback gain at fixed controller and measurement bandwidths and compare it with full-spectrum calculations. The comparison shows that a high mechanical quality factor alone does not guarantee quantitative agreement: the accuracy of the near-resonant approximation depends strongly on the controller and measurement bandwidths. Because finite measurement bandwidth changes both the magnitude and phase of the feedback loop, the analysis separates the near-resonant damping contribution from imprecision-noise reinjection and shows that positive near-resonant feedback damping requires the product of the controller cutoff and measurement bandwidth to exceed the square of the mechanical resonance frequency. Finally, we present a dimensionless map of the gain-optimized high-$Q$ occupation and compare its predictions with full-spectrum optimization. All analytical gains evaluated in this map satisfy the full closed-loop stability criterion for these parameters.
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Optics

Vortex solitons in star networks

Yaroslav V. Kartashov

I consider vortex solitons in two-dimensional star networks created by several one-dimensional line waveguide arrays (or rays) brought in close proximity. First waveguide in each array belongs to the ring of certain radius and its modal field overlaps with modal fields of waveguides from other rays laying on this ring, as well as with modal fields of waveguides in this line array. This creates a system with discrete rotational symmetry that is capable of supporting various localized linear vortex states due to local coupling between waveguides on the central ring, where line arrays approach each other. Localized vortex states emerge from the continuum of the states extended along the rays of the structure upon variation of the radius of the central ring. I show how different vortex modes with progressively increasing topological charges emerge when the number of rays in structure and, therefore, its discrete rotational symmetry increases. Each such linear localized mode gives rise to a family of thresholdless vortex solitons in nonlinear optical medium, whose topological charges are limited by the discrete rotational symmetry of the system. Vortex solitons in star networks exhibit qualitatively different behavior with increasing power depending on whether the propagation constant of linear vortex that gives rise to a family of solitons is located above or below the band of extended states. Stability properties of vortex solitons nontrivially depend on their topological charge and discrete rotational symmetry of the system, showing very different picture from usual ring-like waveguide arrays.
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Optics

Refractive Index Dispersion Fingerprinting via Scanning-Free Parallel Multi-Wavelength SPR on a Single Aluminum Film

Zihao Luo, Zhiying Chen, Yueqian Zhang et al. (+7 more)

Real-time characterization of refractive index (RI) dispersion is pivotal for advanced optical sensing, yet conventional surface plasmon resonance (SPR) platforms are bottlenecked by the narrow bandwidth of noble metals (Au, Ag) and the mechanical instability of sequential scanning. Here, we report a novel Al-based parallel SPR platform that overcomes the bandwidth and temporal constraints of conventional noble-metal systems. Leveraging the unique low-loss broadband response of Al, enabled by the suppression of interband transitions, we engineered a system for simultaneous excitation at 450, 520, and 635 nm. By integrating spectral-angle multiplexing with RGB-channel demultiplexing on a CMOS camera, the platform achieved acquisition of dispersion profiles without mechanical motion. Validated against NaCl solutions, the system demonstrates metrological accuracy and exceptional agreement with Cauchy dispersion models. The proposed architecture eliminates temporal drift and vibration errors, establishing a new benchmark for real-time dispersion characterization. By decoupling sensing from mechanical constraints, this work pioneers a compact, robust framework for next-generation, field-deployable sensors capable of distinguishing complex analytes via their unique spectral signatures.
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All authors Zihao Luo, Zhiying Chen, Yueqian Zhang, Xue Liu, Changsen Sun, Dmitry Kiesewetter, Sergey Krivosheev, Sergey Magazinov, Victor Malyugin, Xue Han

Friday 11 September

Optics · Cross-listed from astro-ph.IM

Sensing ELT petal modes with a discrete beam combiner: an end-to-end theoretical model

Kalaga V. Madhav, Abani Shankar Nayak, Lucas Labadie et al. (+1 more)

The European Southern Observatory's Extremely Large Telescope (ELT), the 39-m telescope under construction in Chile, forms its entrance pupil from 798 hexagonal segments that the six 0.5-m-wide spider arms fragment into six "petals". The low-wind / island effect, adaptive-optics residuals, and mechanical drift imprint an independent piston on each petal. These differential-piston (petal) modes remain largely undetected by the ELT's baseline continuous-pupil wavefront sensors, a major bottleneck for diffraction-limited, high-contrast imaging. This paper presents a complete theoretical model of a single-mode photonic discrete beam combiner (DBC) configured to sense the six petal pistons. The model constructs the coupled-mode description of a two-dimensional evanescently coupled waveguide lattice with six inputs and forty-five outputs and derives its visibility-to-pixel matrix (V2PM); treats the pupil remapping that routes one sub-aperture per petal into the six inputs; develops the five-dimensional petal-mode basis of the fragmented pupil; and propagates the petal modes through the DBC to quantify the sensitivity. Optimising the input-port spacing and interaction length by minimising the V2PM condition number yields a well-conditioned device (CN = 10.4). It recovers petal pistons with unit linear gain over the full +/-lambda/2 (+/-800 nm) unambiguous range and separates the five modes with negligible cross-talk (< 10^-3). For 1% photometric noise, the reconstructed-piston error is 4.7 nm rms at lambda_0 = 1.6 micron. Tested against petal amplitudes from end-to-end ELT simulations (~40-300 nm rms atmospheric residual; ~0.3-1 micron low-wind events), the DBC recovers each piston to a few nm rms at H band, with a two-wavelength extension capturing the larger events. The DBC is therefore a compact, chromatically robust petalometer for the fragmented ELT pupil.
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All authors Kalaga V. Madhav, Abani Shankar Nayak, Lucas Labadie, Robert R. Thomson

Optics

Dynamically-scaled local patch method for numerically simulating the scattering effects of small particles into large beams

Kohei Yamamoto and Ryan DeRosa

Simulating the propagation of a large beam with high spatial resolution is a common challenge in optics due to both computational time and memory demands. While computational time sets a practical limit on what one can simulate, memory resources are an absolute hard limit. In this paper, we report a novel method to overcome a gap in spatial scale between the beam and the relatively small optical disturbance that needs to be modeled, such as those due to particulate contamination. The method splits the entire propagation chain into to two paths: a specular field propagation on coarse grids and scattered fields on fine grids. Especially for the latter, we dynamically apply high-resolution local patches for individual particles. Not limited to particulate contamination, this method is applicable to any tiny discontinuous structures on the beam propagation path without memory overflow triggered.
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Optics · Cross-listed from astro-ph.IM

Photonic Integrated Circuits for the Habitable Worlds Observatory: Science Drivers, Material Platforms, Arrayed-Waveguide Spectrographs, and a Space-Qualification Roadmap

Kalaga Madhav

NASA's Habitable Worlds Observatory (HWO) will require ultraviolet, optical, and near-infrared instruments that are simultaneously compact, mechanically and thermally stable, high-throughput, and replicable at large channel counts. Space-qualified photonic integrated circuits (PICs) and optical fibres are key platforms that can deliver these properties: they manipulate light at the diffraction limit within micron-scale single-mode waveguide circuits. An astrophotonic instrument fully guides the starlight from focal plane to detector, eliminating scatter and ghosts and offering excellent stability with no moving parts. This paper examines how astrophotonics can address the principal science drivers of HWO through four topics: (I) the HWO observing modes best implemented with photonic instruments; (II) the waveguide and fibre materials that can span the demanding 100nm-2.5{\mu}m HWO wavelength range; (III) the potential of arrayed-waveguide-grating (AWG) spectrographs to reach the resolving powers and throughputs HWO science requires; and (IV) the steps needed to space-qualify PICs and fibres against radiation, thermal cycling, vacuum, and launch loads. For each topic, concrete technical requirements are extracted and the current Technology Readiness Level (TRL) is assessed. The main contribution of this paper is to unify these science drivers, candidate-aperture photon budgets, UV-to-near-infrared material platforms, AWG architectures, and space-qualification requirements within a single photon-budget framework that pairs each claimed benefit with a measurable requirement, a TRL, and an environmental test that can retire it. A phased roadmap advances the critical photonic components from their present TRL~2 to -5, depending on platform and application, to the TRL~6 needed at HWO's instrument-definition gate.
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Optics

Transverse-Anderson localization of light in disordered silicon pores

S. Erfanifam, C. Yanik and M. Erfanifam

Transverse light localization of Anderson type through disorders has made intriguing fundamental topics. Toward this, we found that in the disordered porous Si (PSi) a nearly "zero reflection" (from 450 to 900 nm) can be observed. The localization length versus disorder parameter is experimentally visualized and calculated based on a self consistent theory and solution of stochastic Helmholtz equation for electric fields traveling in a transverse disordered media with the results determined to be in a reasonable agreement with experiments. Based on these calculations for different pore diameters in a constant order parameter, diffusion length can vary from 260 nm to 2.4\mu m, accounting as controllability of such structure for further applications in photonic devices. Reflection from ordered PSi structure are evaluated that shows no similar responses to those seen in disordered PSi.
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Optics · Cross-listed from cond-mat.mtrl-sci

Symmetry- and Property-Aware Crystal Generation with Reinforcement Learning for Inverse Materials Design

Ting-Wei Hsu, Arun Bansil and Qimin Yan

The inverse design of crystalline materials ultimately seeks structures with desired physical properties. However, for many functional responses, a favorable numerical value is meaningful only when supported by the symmetry of the underlying crystal. Without the appropriate crystallographic constraints, an apparent response may be ill defined, accidental, or not symmetry protected. Here we introduce SPARC, a symmetry- and property-aware reinforcement learning framework that optimizes physical objectives while preserving the structural conditions required for their realization. We demonstrate SPARC on two complementary tasks. The first targets strong uniaxial dielectric anisotropy, a tensorial response that is well defined only within appropriate crystal classes. The second maximizes the spectroscopic limited maximum efficiency, a scalar device-level objective without a prescribed symmetry class, allowing the framework to identify favorable crystallographic motifs. These results show that symmetry is not merely an additional design constraint, but a physical foundation for generating candidates with meaningful, robust, and realizable functional properties.
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Optics

Versatile Sleeve-and-Bulk Fabrication of Inversely Designed Nanophotonic Structures with High Pattern Transfer Fidelity

Lan Hoang Mai, Radheya Sham Sarode, William G. Eshbaugh et al. (+6 more)

Inverse design is a powerful computational tool for generating nanophotonic devices that should outperform their traditionally designed counterparts. However, translating these theoretical gains into physical devices is challenging because the irregular and non-intuitive features that make inversely designed structures so effective also make them exceptionally difficult to fabricate, typically necessitating substantial process optimization unique to each device design. We describe a versatile two-step nanofabrication process that achieves pattern transfer fidelity in excess of 90% for each of three distinct inverse device designs with no device-specific process optimization.
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All authors Lan Hoang Mai, Radheya Sham Sarode, William G. Eshbaugh, Sulaiman Al Ghadani, Tyler Manfre, Nazifa Tasnim Arony, Joshua M. O. Zide, Matthew F. Doty, Edward B. Flagg

Optics

Momentum microscopy of ultrafast electron emission from a strongly driven optical nanoantenna

Kerstin Harland, Germann Hergert, Zsuzsanna Pápa et al. (+9 more)

Metallic nanostructures in combination with femtosecond lasers are a well-suited platform for the control of photoelectrons by strong and nano-localized driving fields, with high relevance for ultrafast, coherent electron emitters and petahertz electronics. Photoelectron spectroscopy resolves such photoelectron dynamics, but lacks nanoscale spatial resolution, making it only suited for single emitters or homogeneous arrays. We report the first strong-field experiment combining both photoemission electron microscopy and momentum microscopy, two complementary techniques providing spatial and momentum resolution within the same instrument. We apply this new methodology to a double-hole nanoantenna with sub-10 nm apex radii, demonstrating the potential of this approach for the control of photoelectrons in heterogeneous nanostructured samples using few-cycle light fields. Our measurements reveal distinct signatures of two classes of electron trajectories in the near-field. Quiver trajectories result in directed, angularly more focused emission, whereas subcycle trajectories give rise to a broader transverse momentum distribution. Surprisingly, this observation disagrees with previously reported emission characteristics from nanotip emitters, which we classify as a special case of a broader class of curved emitter surfaces driven by ultrashort light fields. This demonstrates both the impact of sophisticated electron detection methods and the potential of strong-field control of electrons in nanoscale geometries.
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All authors Kerstin Harland, Germann Hergert, Zsuzsanna Pápa, Xiaofei Wu, Lina Hansen, Julia Altenburg, Katrin Meier, Arvid Klösgen, Bert Hecht, Jer-Shing Huang, Péter Dombi, Jan Vogelsang

Optics · Cross-listed from quant-ph

Effective Quantization of Lossy Nonlinear Epsilon-Near-Zero Media

Avishi Poddar, Jonas von Milczewski, Durdu O. Guney et al. (+2 more)

In epsilon-near-zero (ENZ) materials, the vanishing real linear permittivity results in the leading-order contribution to the displacement field being nonlinear in the electric field, making conventional canonical quantization approaches highly non-trivial. Existing treatments generally quantize the linear modes first and introduce nonlinear interactions subsequently, an ordering that becomes inadequate in the ENZ regime. Here, we provide, to our knowledge, the first effective single-excitation quantization in which the near-zero linear response, leading nonlinearity, and loss jointly determine the elementary excitation. Using a solvable microscopic atomic system as a theoretical scaffold, we find that this excitation is a polariton: a dressed quasiparticle with partly field and partly material excitations whose coefficients can be parameterized by macroscopic susceptibilities. While this work considers a leading-order $\chi^{(3)}$ nonlinearity, the framework could be generalized to include other nonlinear corrections, including a controllable second-order susceptibility $\chi^{(2)}$ and systematic higher-order contributions $\chi^{(n)}$, $n>2$. Our findings pave the way toward practical applications in quantum photonics, such as single-photon non-demolition detection, by leveraging the strong nonlinearities intrinsic to zero-index materials.
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All authors Avishi Poddar, Jonas von Milczewski, Durdu O. Guney, Sahin K. Özdemir, Susanne F. Yelin

Optics

Unified light-matter metric of molecular and nanophotonic chirality

Kevin N. Moser, Marc R. Bourgeois and David J. Masiello

Signatures of a material object's broken inversion symmetry within its intrinsic excitations and associated optical fields have largely evaded characterization from a perspective that evenly accounts for the inseparability between matter and field dynamics. Here, we formulate a complex-valued pseudoscalar chirality metric that is derived from the coupled electromagnetic and material governing equations, and demonstrate its resolution of the excitational chirality exhibited by the eigenmodes and eigenfields of a family of structurally chiral objects, including those with chirally connected enantiomeric states.
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Optics

Experimental observation of exceptional bound states in the continuum

Shuang Wu, Ruizhi Dong, Nikolay Solodovchenko et al. (+3 more)

We experimentally demonstrate second- and third-order exceptional bound states in the continuum (EP-BICs), formed by the merging of two and three symmetry-protected BICs at an exceptional point (EP). Our passive reciprocal acoustic platform consists of symmetry-protected BIC cavities coupled through an acoustic waveguide and enables independent control of intrinsic loss, radiative loss, and near-field coupling between the cavities. A nonuniformly distributed intrinsic loss provides the non-Hermiticity required for EP formation while preserving decoupling from the waveguide radiation channel. The EP-BICs are probed using both near- and far-field excitation. In the near field, local intracavity excitation directly accesses the symmetry-protected BICs and reveals their spectral evolution. For far-field excitation, we intentionally break the protecting geometrical symmetry, converting the BICs into quasi-BICs and making them accessible through transmission measurements. Extending the system to three cavities with graded intrinsic loss realizes a third-order EP-BIC and yields a larger spectral response to the implemented coupling perturbation. These results establish a passive reciprocal route to higher-order exceptional degeneracies with independent control over intrinsic loss, near-field coupling, and radiative access.
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All authors Shuang Wu, Ruizhi Dong, Nikolay Solodovchenko, Dongxing Mao, Andrey Bogdanov, Yong Li

Optics

Creation and Control of Scattering Singularities in non-Hermitian Systems

Jared Erb, Nadav Shaibe and Steven M. Anlage

The ability to controllably manipulate non-Hermitian wave scattering environments has been used to discover exotic scattering phenomena such as scattering exceptional points and coherent perfect absorption, and create numerous applications including signal routing, filtering, imaging, sensing, wireless power transfer, etc. We introduce the concept that many of these applications and phenomena are fundamentally governed by singularities of the scattering matrix. With this understanding, our demonstrated ability to control the location of scattering singularities can be used to enhance current applications and develop new ones. In generic complex scattering systems, there is an abundance of topologically protected scattering singularities corresponding to complex zeros of various functions of the scattering matrix. We show that with just three tunable parameters we are able to create the conditions for nearly any scattering singularity at arbitrary frequencies in such systems. With five tunable parameters, we demonstrate that more complex scenarios can be accomplished, such as making disparate singularities coincident or placing singularities at different frequencies. A benefit of systems with tunable parameters is that generic complex systems can be re-purposed into exhibiting many different useful properties solely by reconfiguring their tunable parameters. A particularly interesting scattering phenomenon is coherent perfect absorption, where a specific wavefront injected into the system is completely absorbed, with no energy reflected or transmitted through any channel. After creating the conditions for this singularity at an arbitrary preselected frequency, we can find and inject the coherent perfect absorption wavefront and demonstrate output-to-input power ratios as low as 1x10^{-10}, 2x10^{-8}, and 3x10^{-8} in a quarter bowtie billiard with two, three, and four ports, respectively.
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Optics

Multidimensional attosecond clocking near Dirac cones in graphite

Daniel Kroeger, Anna Hassine, Eyal Uzner et al. (+5 more)

Two-color high-harmonic spectroscopy is widely used to access sub-cycle electron dynamics and to retrieve harmonic timing information, including harmonic phases and attochirp across gases, solids, and liquids. However, the dependence of such timing observables on additional laser-control parameters remains largely unexplored. Here, we introduce driving intensity as an additional dimension of two-color harmonic spectroscopy in highly oriented pyrolytic graphite (HOPG). The retrieved attosecond two-color delays maximizing the 4th and 5th harmonic yields evolve systematically and differently with driving intensity. Semiconductor Bloch-equation calculations reproduce these trends and reveal a pronounced sensitivity of the intensity-dependent delays to the electronic band dispersion. Our results demonstrate multidimensional attosecond clocking near Dirac cones and establish intensity-dependent two-color delays as a sensitive observable for band-dispersion in quantum materials.
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All authors Daniel Kroeger, Anna Hassine, Eyal Uzner, Camilo Granados, Marcelo F. Ciappina, Ofer Neufeld, Michael Krüger, Zhaopin Chen