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Sunday 6 September

Optics

Energy-scalable single-burst attosecond emission at kiloelectronvolt photon energies

Kaito Nishimiya and Eiji J. Takahashi

Attosecond soft-X-ray pulses at kiloelectronvolt photon energies would provide direct access to the L-edges of transition metals, enabling element-specific studies of charge, spin, and orbital dynamics on their intrinsic timescales. However, attosecond emission in this spectral region has remained elusive because the only phase-matched keV high-harmonic source demonstrated to date employed multicycle driving pulses without carrier-envelope-phase (CEP) control. A long-standing gap has therefore persisted between keV photon energies and CEP-controlled attosecond emission. Here, we bridge this gap using a CEP-stabilized mid-infrared laser system with pulse durations tunable to the sub-cycle regime. Through phase-matched highharmonic generation in low-pressure neutral helium under meter-scale loose-focusing conditions, we generate coherent soft-X-ray continua reaching 1.2 keV. Crucially, we observe CEP-dependent spectral modulation that reaches into the transition-metal L-edge region, providing experimental evidence consistent with the generation of isolated attosecond pulses. To demonstrate the capabilities of our source, we perform broadband soft-X-ray absorption spectroscopy spanning the Ti, Fe, Co, and Ni L-edges, as well as the O K-edge, and resolve near-edge fine structures. By combining meter-scale loose focusing with low-pressure phase matching, our approach addresses key energy-scaling limitations of previous keV high-harmonic sources and establishes a phase-matched, CEP-controlled keV soft-X-ray platform for attosecond spectroscopy of magnetic, quantum, and strongly correlated materials.
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Optics · Cross-listed from quant-ph

Telecom-Integrated Photonic Memory Operating Near the Mechanical Ground State

Jindao Tang, Bo Jing, Liping Zeng et al. (+11 more)

Scalable quantum networks require quantum memories that are chip-integrated, telecom-band compatible, and capable of flexible retrieval. Nanofabricated mechanical resonators meet these criteria. They offer independent tunability of optical and mechanical modes, long-lived phonon states, and design flexibility beyond atomic systems, making them strong candidates for practical integrated quantum memory. Here, we demonstrate an on-chip, absorptive optomechanical memory for telecom-band photons, based on optomechanically induced transparency (OMIT) and operating near the mechanical ground state. The device stores telecom-band photons, demonstrating compatibility with external photon sources at the few-photon level, while enabling on-demand retrieval. By placing the device in a dilution refrigerator at 20 mK and tailoring the control field to suppress optical heating, we achieve a remarkably low phonon occupancy of just 0.32 during the storage process. Our results lay the groundwork for scalable, phonon-based quantum memory devices and open new avenues for integrating mechanical systems into practical quantum network architectures.
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All authors Jindao Tang, Bo Jing, Liping Zeng, Peiqin Chen, Hengrui Liang, Yifei Zhang, Xinyao Xu, Qizhi Cai, Xueying Zhang, Qiang Zhou, You Wang, Haizhi Song, Guangcan Guo, Guangwei Deng

Saturday 5 September

Optics

Cell Reproduction in a Dark Optical Trap

Ariel Hertz, Gabriel Dias, Carlos L. R. Fragoso et al. (+3 more)

Optical tweezers are a versatile tool in the domain of cytology, enabling trapping and manipulation of individual cells. However, the incidence of laser light causes photodamage to biological matter, even when operating at low optical powers and over short periods of time. Here, we demonstrate stable trapping of single living Saccharomyces cerevisiae yeast cells in vitro using a dark optical trap operating in the repulsive regime of light-matter interactions. In contrast to standard tweezers, our dark optical trap confines cells for hours with negligible disruption to their morphology and reproduction cycle, opening up new possibilities for long duration experiments with living organisms such as the observation of cell reproduction under laser trapping.
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All authors Ariel Hertz, Gabriel Dias, Carlos L. R. Fragoso, Anna De Falco, A. Z. Khoury, Thiago Guerreiro

Optics

Optimization Algorithm-Assisted Nanostructure Engineering for Performance Enhancement of Thin-Film Solar Cells

Abyaz Karim, Sajid Ahmed Chowdhury, A. F. M. Afnan Uzzaman Sheikh et al. (+2 more)

A computation-based study is presented that utilizes the finite-difference time-domain (FDTD) method to perform optical simulations. These simulations were used to observe the effects of core-shell nanostructures with triangular cross-sections embedded inside the light absorbing layer of thin-film solar cells (TFSCs), for improving the optoelectronic performance. Despite extensive research, the relationship between the geometric parameters of light trapping nanostructures and TFSC performance is not yet fully elucidated. To assist in finding the optimal set of parameters, optimization algorithms are used to find a set of parameters that provide maximal short-circuit current density ($J_{SC}$). Three separate algorithms were applied, and the results were scrutinized in-depth with a sensitivity analysis, observing the effects of small changes in the optimal parameters. The optimal parameters of the nanostructure produced $J_{SC}$ values ranging from 28.90 to 35.39 mA/cm$^2$ compared to 13.69 mA/cm$^2$ for a reference TFSC with no nanostructure present. From the results of this study, it can be inferred that optimized periodic grating structures can provide substantial improvement in performance of TFSCs.
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All authors Abyaz Karim, Sajid Ahmed Chowdhury, A. F. M. Afnan Uzzaman Sheikh, Asif Al Suny, Mustafa Habib Chowdhury

Optics · Cross-listed from physics.pop-ph

Project Setu: 3D Multi-Physics Design and Scaled Structural Analysis for a Relativistic Lightsail Architecture

Prashant Suresh Kamble

Deep-space exploration beyond the solar system requires eliminating chemical propellant mass penalties to achieve relativistic flight velocities (0.166c at 180 s, reaching the mission target of 0.20c at 227 s). This study presents a 3D multi-physics numerical framework for a 4.0-meter circular lightsail propelled by a 100 GW ground laser array, coupling 3D Maxwell FDTD wave optics, non-linear membrane mechanics, and Stefan-Boltzmann thermal radiation in ANSYS Mechanical APDL and Ansys Lumerical. A four-level grid convergence study establishes numerical independence with an ASME GCI_21 of 0.13%, resolving peak membrane stresses of 530.88 MPa with a 3.77x safety factor against stoichiometric Si3N4 tensile failure. With optical absorption constrained to 10 ppm (A = 1.0 x 10^-5), the steady-state core temperature stabilizes at 923.02 K (0.44% deviation from radiation theory), maintaining a +1,247 K margin below sublimation, while fundamental drumhead modal resonance (7.92 Hz) provides a 7.92x safety buffer against laser jitter. The electrodynamic radiation pressure formulation is cross-verified against published flight telemetry from JAXA IKAROS and NASA LightSail 2 within 0.12% and 2.13%, confirming classical momentum transfer modeling across solar and beamed propulsion regimes.
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Optics

Helicity-engineered nonlinear optical responses in photo-excited topological semimetals

Roshan Kumar Thakur, Prachi Venkat, Amar Bharti et al. (+1 more)

Topological materials provide a transformative arena for light-driven control of electronic motion; yet, direct manipulation of electron dynamics on sub-cycle timescale remains a significant challenge. We demonstrate that the strong-field-driven high-harmonic generation of a Weyl semimetal can be controlled and manipulated through bicircular pump-probe driving fields. While a lone probe pulse generates exclusively odd-order harmonics, the addition of a pump pulse triggers a series of sidebands arising from nonlinear frequency mixing of pump and probe photons. Our results reveal that the sideband intensities are highly sensitive to the relative helicity of the pulses and the orientation of the polarization plane. This sensitivity stems from the chiral nature of the Weyl nodes, which couples efficiently to the light's helicity only when the node-separation axis is perpendicular to the polarization plane. Furthermore, the significant suppression of sideband intensity with increasing pump-probe delay identifies these features as a potential clock for electron-hole decoherence. These findings establish frequency-mixed high-harmonic generation as a sensitive probe of chiral quantum dynamics and suggest a robust framework for manipulating topological currents via structured light, with implications for lightwave electronics and ultrafast quantum information processing.
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All authors Roshan Kumar Thakur, Prachi Venkat, Amar Bharti, Gopal Dixit

Optics

Construction-Constrained Bernstein Synthesis of Joint Pitch-Width RDL Spiral Inductors for High-Q mmWave FoWLP Applications

Shuhang Chen, Xinmeng Wang, Yuchong Sun et al. (+1 more)

We present a construction-constrained Bernstein framework for joint pitch-width synthesis of planar spiral inductors. A positive cubic Bernstein profile is integrated to prescribe a monotonic radial trajectory, while an independent Bernstein profile controls the conductor width. The nonnegativity, partition-of-unity, and convex-hull properties of the Bernstein basis convert endpoint, winding-direction, and width requirements into algebraic constraints. Embedded in differential evolution (DE), these constraints reject inadmissible candidates before full-wave evaluation, focusing expensive solver calls on geometries that satisfy the construction rules. The method is demonstrated on a two-turn mmWave inductor implemented in the redistribution layer (RDL) of fan-out wafer-level packaging (FoWLP), with the quality factor selected as the optimization objective. Searching the constrained Bernstein design space with DE yields a simulated Q of 34.85 at 30 GHz, compared with 29.66 for a uniform Archimedean baseline under the same stack, footprint, and ports. This corresponds to a 17.5% improvement while reducing planar copper area by 1.53%. The optimized response maintains Q >= 30 from 16 to 49 GHz.
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All authors Shuhang Chen, Xinmeng Wang, Yuchong Sun, Qi Zhu

Optics · Cross-listed from cond-mat.other

Multiplicity of surface polariton configurations in bi-isotropic media with anomalous Hall current

Alex Q. Costa, Pedro D. S. Silva and Manoel M. Ferreira Jr

In this work, we investigate surface polaritons (SPs) arising at the interface between a simple dielectric and a bi-isotropic medium, in the lossless regime and in the presence of small losses. For the former, non-Dyakonov surface polaritons can arise for positive permittivities and magnetoelectric parameters. General restrictions on the permittivities and bi-isotropic parameter (existence conditions) are derived. For the latter, the effect of small losses is considered, and the characteristic surface plasmon-polariton lengths are discussed. The propagation length can exhibit a local maximum for specific values of the magnetoelectric parameter, an unusual new behavior that can be regarded as a signature of these chiral surface polaritons. Surface waves in an interface involving a bi- isotropic medium with an anomalous Hall effect (AHE) are also examined. Multiple configurations for their occurrence are obtained, revealing a richer scenario with distinct regimes of propagation and coexistence in the parameter space. The presence of a non-null AHE contribution creates a magnetoelectric range for which the surface wave propagation is forbidden, providing an additional signature of surface-polariton propagation in bi-isotropic media with an AHE contribution.
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Optics · Cross-listed from physics.atom-ph

Floquet Interpretation of Avoided Crossings in AC Stark-Shifted Rydberg-EIT Spectra

Rajavardhan Talashila, Nikunjkumar Prajapati, Noah Schlossberger et al. (+1 more)

We present a combined experimental and Floquet-theoretical study of avoided crossings in the AC Stark-shifted electromagnetically induced transparency (EIT) spectra of Rydberg atoms. Observed avoided-crossing structures cannot be fully explained by conventional AC Stark maps alone, which provide the energy shifts but do not reveal the underlying state composition and coupling pathways. Using the Shirley method, we analyze the Floquet eigenstates to establish a direct connection between the measured spectra and the underlying dressed-state dynamics. By tracking the evolution of state mixing, bare-state composition, and dominant higher-order Floquet coupling pathways, we reveal the physical mechanisms responsible for the formation of avoided crossings across different principal quantum numbers and RF frequencies. Our results demonstrate that Floquet-eigenstate analysis provides a powerful framework for interpreting complex AC Stark-shifted Rydberg-EIT spectra and the underlying higher-order Floquet coupling interactions.
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All authors Rajavardhan Talashila, Nikunjkumar Prajapati, Noah Schlossberger, Christopher L. Holloway

Optics

Representation of arbitrary rational functions and polynomials by non-Foster resistor-capacitor-inductor networks

Andrew Mackay

The Bott-Duffin theorem shows that any arbitrary positive real rational function of finite order, representing a passive network, can be represented by a finite number of positive value resistors, capacitors and inductors. It is shown here that if the positivity restriction is lifted, any rational function or polynomial of any order may be represented by a network of (possibly negative) inductors, capacitors and resistors. When there are no repeated roots this is a sum of simple sub-circuits each of which contains no more than four components. When there are repeated roots a more complex circuit is required, here featuring iterated Wheatstone bridges of special form.
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Optics

Motion-Tracking Terahertz Time-Domain Spectroscopy Enabled by Time-Programmable Frequency Combs for Moving-Object Sensing

Riku Shibata, Shun Fujii, Tomofumi Ikari et al. (+1 more)

Terahertz time-domain spectroscopy (THz-TDS) provides direct access to both spectral information and time-of-flight features, making it attractive for dynamic sensing. However, conventional high-speed THz-TDS methods typically rely on a fixed delay trajectory, limiting their ability to selectively acquire only the relevant temporal window while tracking target motion. Here, we demonstrate motion-tracking THz-TDS based on time-programmable frequency combs (TPFCs), in which the THz measurement window is actively locked to a moving time-domain waveform. By continuously modulating the phase-lock set point of one TPFC, we perform real-time apodized acquisition of a specific temporal window centered on the main THz peak at rates up to 308 Hz. Simultaneously, the residual peak position within the window is detected in real time and fed back to the other comb, enabling the measurement window to follow target displacements exceeding the original acquisition window. The feedback command together with the residual peak position further enables reconstruction of the relative target displacement. As a proof-of-concept demonstration, we use a moving gold mirror to simulate respiration- and heartbeat-related motion superimposed on a much larger displacement representing body motion, and successfully resolve the two vital-sign-related components from the measured displacement. This work extends arbitrary-delay control with TPFCs to THz-TDS and establishes a motion-compensated spectroscopy platform for simultaneous displacement tracking and THz waveform acquisition.
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All authors Riku Shibata, Shun Fujii, Tomofumi Ikari, Shinichi Watanabe

Optics · Cross-listed from quant-ph

Data-driven structural diagnostics and autonomous alignment of complex optical systems

Peng Zhu, Chen Chen, Shuchang Ma et al. (+3 more)

The quest for autonomous alignment and maintenance of complex free-space optical systems is increasingly urgent for large-scale neutral-atom quantum processors. Leveraging a high-finesse optical cavity as a sensitive probe, we introduce a data-driven framework for structural diagnostics and closed-loop control that achieves cold-start convergence within tens of seconds. These results establish a rapid, scalable diagnostic-control methodology for autonomous alignment and continuous maintenance of complex free-space optical architectures.
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All authors Peng Zhu, Chen Chen, Shuchang Ma, Dezhou Deng, J. F. Chen, Peng Chen

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

The electromagnetic stress tensor in cubic crystals and amorphous solids

Richard Dengler

The electromagnetic vacuum stress tensor in a system consisting of classical point-like atoms on a cubic lattice is derived directly from the electric field and, alternatively, using the known more phenomenological formula involving the (usually unknown) derivative of the dielectric tensor. The results agree. The stress tensor contains a nontrivial constant and therefore cannot be obtained from macroscopic electrodynamics alone. A system consisting of a mosaic of randomly oriented grains of a cubic crystal is used as a model of an amorphous solid. The electromagnetic stress tensor in this system is deduced by averaging the corresponding quantity in a cubic crystal over all orientations. Two components remain: the component in the direction of the electric field and the component perpendicular to it. The transverse component agrees with the analogous quantity for liquids derived by Peierls in an entirely different way.
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Optics

Optoelectronic Reservoir Computing with an On-Chip True-Time-Delay Element

Ahmad Murad, Shadad Watad and Alina Karabchevsky

Compact delay elements remain a central challenge in photonic neuromorphic processors. Here, we demonstrate an optoelectronic delayed-feedback reservoir computer that incorporates a foundry-fabricated silicon nitride (Si$_3$N$_4$) true-time-delay circuit within its feedback loop. Eight cascaded Archimedean spirals provide a \SI{1.76}{\metre} on-chip optical path and a calculated passive group delay of \SI{11.63}{\nano\second}. At a feedback gain of $G=0.0223$, the system classifies sinusoidal and square waveforms without error (word error rate, WER\,$=$\,0 across all cross-validation folds), predicts the Mackey–Glass chaotic series with a best-fold normalized mean-square error (NMSE) of $0.0082$, and performs nine-class Japanese Vowels speaker classification with WER\,$=$\,0.0898. We also introduce a subcarrier phase-encoding method that maps the calculated $0.232\pi$ spiral-to-reference phase contrast onto the measured reservoir states through deliberate aliasing, achieving NMSE\,$=$\,0.0767 and WER\,$=$\,0 without increasing the insertion-loss-limited feedback gain. These results show that on-chip propagation delay in Si$_3$N$_4$ can operate as a functional component of an optoelectronic reservoir computer and motivate lower-loss, more-integrated implementations.
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Optics

Rapid and high-sensitive NV-based microwave field imaging via digital lock-in amplification for on-chip microstrip diagnostics

Zijin Fu, Yanjie Liu, Hongliang Wu et al. (+6 more)

High-resolution, high-sensitivity microwave (MW) magnetic field imaging is indispensable for non-destructive integrated circuit (IC) testing, radio-frequency device characterization, and spintronic research. Yet, the practical utility of these techniques is severely constrained by the pervasive challenge of isolating weak magnetic signatures from intense optical and electronic noise, which fundamentally limits both acquisition speed and detection sensitivity. Here, we overcome this barrier by introducing a wide-field imaging scheme based on an ensemble of diamond nitrogen-vacancy (NV) centers, synergistically combined with digital lock-in amplification (DLA). By exploiting digital demodulation, the DLA precisely extracts the MW-field response at a specific modulation frequency from background noise (e.g., laser intensity fluctuations), dramatically improving the signal-to-noise ratio (SNR). Consequently, our system attains a magnetic field sensitivity of 126 nT/$\sqrt(Hz)$. Critically, the unprecedented SNR permits a pixel dwell time of under one millisecond, allowing full-field images to be acquired within seconds-more than an order of magnitude faster than state-of-the-art NV-based wide-field techniques. This combination of speed, sensitivity, and micron-scale spatial resolution (1.6 $\mu$m) paves the way for quasi-real-time, non-invasive diagnostics of dynamic MW devices and integrated circuits.
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All authors Zijin Fu, Yanjie Liu, Hongliang Wu, Yuchen Han, Zhengtao Wang, Haolin Li, Dezhi Zheng, Bo Zhang, Jun Zhang

Optics

Physical policy gradient theorem for in situ stochastic-adjoint training

William Tuxbury and Zin Lin

In situ adjoint training extracts parameter gradients directly from measurement, but has so far been limited to reciprocal or restricted systems. Here, we introduce the physical counterpart of the policy gradient theorem: a stochastic-adjoint gradient estimator that lifts these constraints by trading reciprocity for nondegenerate diffusion. As validation, we train a nonlinear resonator network, whose own dynamics supply the policy, against antagonistic temporal modulations with gradients from measured stochastic trajectories alone, without finite differences or a separate adjoint experiment.
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Friday 4 September

Optics

Phase-aware Inverse Design for Silicon Photonic Logic Gates

Ary Portes, Narges Dalvand, Felipe M. F. Teixeira et al. (+4 more)

Inverse design has emerged as a powerful strategy for realizing compact photonic devices; however, its application to logic operations remains constrained by challenges in physical interpretability, architectural generality, and experimental validation. This work introduces an experimentally validated, unified, and physics-driven inverse design framework that implements all fundamental Boolean logic gates within a single silicon photonic architecture. Devices are fabricated within a 2 x 2 um^2 design region on a silicon-on-insulator platform, representing one of the smallest areas reported for photonic logic elements. By integrating amplitude, phase, and energy conservation into a composite figure of merit, the proposed approach enables direct control over constructive and destructive interference. Consequently, all logic functions, including XOR and three-input NAND/NOR operations, are achieved using a standardized configuration with two logical inputs and a bias port. Experimental results exhibit good agreement with numerical simulations across the C-band, confirming both the predictive accuracy and fabrication robustness of the method. Performance benchmarking reveals competitive contrast ratios compared to previous implementations, while providing a unified and scalable design strategy. These findings establish a physically interpretable and experimentally validated paradigm for inverse-designed photonic logic, advancing the development of compact, integrated optical computing systems.
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All authors Ary Portes, Narges Dalvand, Felipe M. F. Teixeira, Omar P Vilela Neto, Julian L. Pita Ruiz, Michael Menard, Jhonattan C. Ramirez

Optics · Cross-listed from quant-ph

Squeezed light and coherent feedback enhanced multiparameter quantum estimation in a double-cavity optomechanics: steady and dynamical states

Hamza Harraf, Mohamed Amazioug, Amjad Sohail et al. (+2 more)

Multiparameter quantum estimation in open optomechanical systems is fundamentally constrained by dissipation, thermal fluctuations, and measurement incompatibility. In this work, we investigate a coupled cavity optomechanical platform in which two mechanical modes interact with driven optical cavities, two mode squeezed vacuum, intracavity degenerate parametric amplification, and coherent optical feedback. Using the continuous variable Gaussian state formalism, we derive the linearized quantum Langevin dynamics and steady state covariance matrix and evaluate the quantum Fisher information matrices associated with simultaneous estimation of the optomechanical coupling strength and cavity dissipation rate. We characterize the precision bounds using the symmetric and right logarithmic derivative formalisms and employ $\mathcal{B}_{\rm MI}=\max\{\mathcal{B}_S,\mathcal{B}_R\}$ as a comparative figure of merit within the SLD/RLD framework. We find that parametric amplification can substantially reduce the most informative bound, $\mathcal{B}_{\rm MI}$, thereby enhancing multiparameter estimation precision over a broad range of operating conditions. Coherent feedback can further reduce $\mathcal{B}_{\rm MI}$ and improve the estimation precision, particularly in the strong feedback regime. Moreover, the simultaneous presence of coherent feedback, parametric amplification, and squeezed light injection provides a combined mechanism for controlling quantum fluctuations and parameter dependent correlations, leading to enhanced and more robust multiparameter estimation. We further analyze the dynamical and steady state regimes to identify the parameter regions in which these quantum resources provide the largest metrological gain. Our results establish coupled cavity optomechanics as a flexible platform for quantum-noise engineering in multiparameter sensing.
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All authors Hamza Harraf, Mohamed Amazioug, Amjad Sohail, Mojtaba Mazaheri, Rachid Ahl Laamara

Optics

Screening bolt loosening in a four-bolt plate with global FRF correlation and local FRAC maps from full-field laser Doppler vibrometry

Berkay Kullukcu, Robin Pianowski, Mehmet Sait Özer et al. (+2 more)

Full-field laser Doppler vibrometry (LDV) can reveal how bolt torque loss redistributes a frequency response function (FRF) over an entire structure rather than only at a few sensor positions. This work presents a screening procedure for a four-bolt aluminum plate using pointwise amplitude and phase exports of scanned H1 FRFs. Candidate resonances were selected from the all-tight spatial RMS spectrum and tracked in four single-bolt 0 Nm cases. Seven baseline responses remained trackable within prescribed group-specific search windows and were retained as experimental resonance groups RG1-RG7; a dimensionless plate-frequency coefficient was reported alongside each measured frequency. Global changes were quantified using amplitude-only and complex, phase-retaining modal-assurance dissimilarities, and local changes were evaluated using matched-window FRAC-deficit maps and a normalized hotspot-area fraction. The retained groups separate into low-, intermediate-, and high-distortion responses, while the local maps distinguish compact joint-centered changes from distributed FRF redistribution. The workflow therefore links global FRF distortion with spatially resolved interpretation without relying on a trained classifier or specimen-specific node labels.
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All authors Berkay Kullukcu, Robin Pianowski, Mehmet Sait Özer, Ercan Altinsoy, Dina Hannebauer

Optics

Bounds on Propagation Constants in Dielectric Gratings

Ehsan Faghihifar

We establish analytical bounds on the normalized longitudinal propagation constants $\beta=k_z/k_0$ of modes in lossless dielectric diffraction gratings. If $\epsilon_{\max}$ denotes the maximum relative permittivity, we show that regular modes ($\beta^2\in\mathbb{R}$) satisfy $\beta^2\le\epsilon_{\max}$ despite the lack of a scalar dispersion relation. We further show that the so-called ghost modes ($\beta^2\notin\mathbb{R}$), admitted by the non-Hermitian nature of the associated eigenproblem, satisfy $|\mathrm{Re}(\beta)|\le\sqrt{\epsilon_{\max}}/2$. Both bounds are obtained directly from the Fourier-series formulation of the fully coupled vectorial eigenproblem.
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Optics

Fabrication-Aware Design of a Hybrid Metasurface-Bragg Mirror for Low-Noise Precision Optics

Mika Gaedtke, Christian Kranhold, Markus Walther et al. (+3 more)

High-reflectivity coatings for precision interferometry must simultaneously minimize optical losses and thermally driven displacement noise. Dielectric Bragg mirrors provide robust high reflectance but rely on thick multilayer coatings, whereas metasurface mirrors provide high reflectance and low noise but are sensitive to fabrication-induced deviations. A fabrication-aware photonic design framework is introduced that combines a resonant single-layer metasurface, an etch-stop layer, an antiresonant spacer, and a reduced Bragg reflector. Fabrication effects, including geometric tolerances and line-edge roughness, are explicitly considered in the optical design. Full-wave electromagnetic simulations are combined with a truncated-Gaussian Monte Carlo analysis to determine the performance distribution under the assumed fabrication conditions. The ideal metasurface design achieves a modeled non-reflected power of $1-R<10^{-5}$. After roughness-aware reoptimization, the modeled non-reflected power remains below $1.04\cdot10^{-4}$ at $80\%$ fabrication yield. For the cryogenic ETpathfinder gravitational-wave testbed, two Bragg layer pairs reduce the non-reflected power of the complete stack to approximately $6.6\,\mathrm{ppm}$. The estimated thermal displacement-noise amplitude spectral density is $1.97\cdot10^{-20}\,\mathrm{m/\sqrt{Hz}}$ at $100\,\mathrm{Hz}$. The architecture connects fabrication robustness, optical performance, and thermal-noise reduction within a single design framework.
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All authors Mika Gaedtke, Christian Kranhold, Markus Walther, Falk Eilenberger, Stefanie Kroker, Thomas Siefke

Optics

Fisher-information retention under local driving in non-Hermitian feed-forward chains

Qingrui Bai, Zhichao Li and Junlong Kou

When local drive hardware is installed before a sensing task is revealed, directional non-Hermitian buildup creates a tradeoff between targeted preparation and spatial coverage. We quantify this tradeoff for stable linear scatterers with proper complex Gaussian output statistics. For parameters encoded in the internal generator, and at fixed coherent internal resource, the drive hardware enters the optimized mean-response Fisher information only through the projector onto the internally reachable subspace, while the preparation Gramian sets the source cost. In an on-resonance feed-forward chain, nested Green-function columns decompose into disjoint port intervals, and the site-local retention factors in each interval sum exactly to unity. Directionality concentrates this unit downstream, so the worst-site retention decays exponentially when one port serves many sites; for $m$ equal intervals, a single probe shared by all tasks has a worst-site retention lower by a further factor $m$ than task-specific reoptimization. Joint source-power and internal-resource constraints connect this fixed-resource law to source-limited preparation. A noisy RLC/VCCS model illustrates the retention law with stored electromagnetic energy, covariance Fisher information, and component disorder. The resulting bounds turn directional buildup into a port-layout criterion: source savings for a selected task are accompanied by a spatial coverage cost for tasks unknown at the hardware-design stage.
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Optics

Sub-2-Cycle, Terawatt Pulses via Double-Stage Multi-Pass Cell Compression of an Yb Laser

Victor Koltalo, Jaismeen Kaur, Louis Daniault et al. (+8 more)

We report a terawatt-class, sub-2-cycle post-compressed Yb-based laser system operating at kHz repetition rate. 18 mJ, 400 fs pulses delivered at 1 kHz by a commercial Yb:YAG laser are spectrally broadened and temporally compressed in a double-stage multi-pass cell setup featuring an argon-filled Herriott-type cell followed by a helium-filled array-type cell, achieving an overall compression factor of 65. The resulting compressed pulses are measured to have 6.2 fs duration (1.8 optical cycles at 1030 nm) and 12.5 mJ energy, corresponding to 1.4 TW effective peak power. To the best of our knowledge, this constitutes the highest peak power reported to date for a few-cycle, kHz-repetition-rate, post-compressed Yb laser system. Focused intensity measurements yield a normalized vector potential of a0 = 3.0, confirming the applicability of this light source for laser wakefield acceleration.
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All authors Victor Koltalo, Jaismeen Kaur, Louis Daniault, Antoine Cavagna, Mickael Allemand, Florent Pallas, Antoine Courjaud, Emilien Gontier, Cédric Sire, François Sylla, Rodrigo Lopez-Martens

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

Nonreciprocal plasmonic response of drift-biased two-dimensional metals

Gonzalo Álvarez-Pérez and Joel D. Cox

We develop a nonlocal electrodynamic framework for drift-biased two-dimensional electron gases (2DEGs) with Dirac (linear) and parabolic (quadratic) dispersions, deriving closed-form drift-dependent conductivity tensors from the Boltzmann transport equation. We obtain the plasmon dispersion and near-field emission of a point dipole, revealing nonreciprocal propagation in both systems. At equal drift parameter, the parabolic 2DEG exhibits stronger nonreciprocity than the Dirac system, although we find that a larger drift parameter does not by itself produce stronger nonreciprocity: the response is set by the interplay of drift and plasmon nonlocality. As such, the combination of strong nonlocality and experimentally accessible drift velocities of semiconductor 2DEGs identifies parabolic systems as a promising platform for tunable, nonreciprocal plasmonics.
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Optics

Relaxing Coherence Requirements on Laser Sources for Nanoscopy through Optical Fiber Technique

Kaifa Xin, Mengdie Hou, Ao Yang et al. (+8 more)

High numerical-aperture (NA) focusing of cylindrical vector beams (CVBs) typically requires costly, high-quality lasers to supply a stable vector pupil field. Here, we introduce fiber-conditioned vectorial nanofocusing, in which an optical-fiber-based mode-selective coupler projects a strongly distorted beam of a diode that costs two orders of magnitude less than the reference laser into radially or azimuthally polarized CVBs. A three-tolerance analysis clarifies its operating principle by establishing separate requirements for spatial state, temporal coherence and residual wavefront error. The resulting fields reproduce expected high-NA focal signatures and generate orientation-sensitive single-molecule excitation patterns consistent with reference-laser measurements, lowering the barrier to structured-light experiments.
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All authors Kaifa Xin, Mengdie Hou, Ao Yang, Márton Gelléri, Hyun-Keun Lee, Antonio Virgilio Failla, Jiafeng Lu, Xianglong Zeng, Mischa Bonn, Jesper Lægsgaard, Xiaomin Liu

Optics

Frugal Effective Models for Nanophotonic Scattering: Optimizing Global Polarizability Matrices for Metasurface Design

Sofia Ponomareva and Peter R. Wiecha

Accurate nano-photonics simulations of large scale devices like optical metasurfaces require high accuracy reduced models for the device constituents. We present an automated framework for the optimization of Global Polarizability Matrix (GPM) models, which represent a complex scatterer as a small set of non-local effective dipoles. Our goal is to find the most frugal model that reproduces a particle's scattering response within a user-defined accuracy. The method iteratively removes redundant dipoles while re-adapting the positions of the remaining ones via gradient based optimization, stopping at the smallest model that still meets the target. Automatic differentiation, combined with an untrained neural network that reparametrizes the dipole positions, helps to place the dipoles at physically intuitive locations. We demonstrate the versatility of this approach across diverse geometries, from two dimensional ridges over simple spheres to complex three-dimensional particles, achieving compression factors of typically two orders of magnitude compared to full-wave simulations, for target accuracies in the order of few percent. We finally demonstrate how accurate, frugal effective models enable large-scale meta-deflector optimization without periodic approximations. This robust recipe for constructing frugal effective models paves the way for the rapid simulation of large-scale photonic assemblies, required for example for metasurface design.
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Optics

Modulation-Frequency Dependence of Spatial Resolution in Optical Correlation-Domain Reflectometry

Keisuke Motoda, Takaki Kiyozumi and Yosuke Mizuno

The spatial resolution of optical correlation-domain reflectometry (OCDR) has conventionally been described by an expression that is independent of the modulation frequency $f_m$, source linewidth $\delta\nu$, and receiver resolution bandwidth (RBW). However, our previous measurements showed that the spatial resolution $\Delta z$ improves with increasing $f_m$. Here, we develop a theoretical model for OCDR with a frequency shifter by evaluating the electrical power detected by an electrical spectrum analyzer and explicitly including $\delta\nu$ and the RBW $B$. The model predicts two regimes. At low $f_m$, $\Delta z$ decreases approximately in proportion to $1/f_m$, with the proportionality determined by the combined source and receiver spectral response. At high $f_m$, $\Delta z$ approaches a constant value determined by the modulation amplitude $\Delta f$ and independent of the source linewidth and RBW filter. Measurements at RBW = 1 MHz reproduced the transition between these regimes over correlation orders up to 2048. At RBW = 10 MHz, a Voigt representation of the spectral response overestimated $\Delta z$, whereas direct use of the measured unmodulated beat spectrum reduced the discrepancy to approximately 10 to 20%. These results provide a quantitative description of the modulation-frequency dependence of OCDR spatial resolution and clarify its trade-off with measurement range.
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Optics · Cross-listed from quant-ph

Nitrogen Vacancy Centers in Diamond for Quantum Biosensing: Magnetometry Techniques, Platforms and Applications

Sirsendu Ghosal, Umakant Prajapati, Sachin Negi et al. (+3 more)

Quantum sensing using nitrogen-vacancy (NV) centers in diamond has emerged as a powerful platform for detecting ultra-low magnetic fields under ambient conditions. Owing to their long spin coherence times, optical addressability, and compatibility with aqueous environments, it has found widespread applications in biosensing and bio-imaging. This review presents the fundamental principles and recent advances in NV-based quantum magnetometry for biosensing applications, with a particular focus on measurements in aqueous medium and at cellular and molecular length scales. We discuss the underlying spin physics of NV centers and highlight two primary detection modalities: optically detected magnetic resonance (ODMR) and T1 relaxometry-based sensing and how these approaches aids in the detection of both static magnetic fields and dynamic magnetic noise arising from biological processes. The review explores key application areas, including nanoscale nuclear magnetic resonance (NMR), monitoring of neural activity, detection of abnormal or rogue cells using NV-based platforms etc. In addition, strategies for enhancing sensitivity, such as surface functionalization of nanodiamonds, femtosecond (fs) laser-written photonic structures, and integration with microfluidic and lab-on-chip systems have also been discussed in depth. We also address the critical challenges, including surface-induced decoherence, charge-state instability, and signal-to-noise limitations in biofluids associated with NV-based biosensing applications. Finally, we outline future prospects, highlighting how NV-based magnetic biosensing provides a promising pathway for translating quantum sensing technologies into practical biomedical applications.
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All authors Sirsendu Ghosal, Umakant Prajapati, Sachin Negi, Saifian Farooq Bhat, Thejas B, Vibhav Bharadwaj

Optics

Research and simulation of analytical polarization control enabled by optical computing on an integrated photonics chip

Xueying Ren, Meinan Guo, Xuyang Wang et al. (+8 more)

Dynamic polarization controllers are key devices with broad applications in many fields. However, most on-chip polarization controllers still rely on traditional blind-search methods, whereas analytical optical-computing approaches remain insufficiently explored, particularly with respect to calibration and endless polarization control. With the accurate relative phase of Mach-Zehnder interferometer (MZI) being fully controllable on an integrated photonics chip, we present an analytical polarization control (APC) method using four phase shifters and optical computing, eliminating the need for the traditional inefficient blind-search procedure. The basic structures and operations of APC are clarified. The proposed calibration method and endless control method enable continuous APC while compensating for phase differences within the MZI structures. We simulate the influence of the endless control unit on polarization control and quantify the effect of the fourth phase difference on the output extinction ratio. With the fourth phase shifter, the phase difference encountered during Stokes vector measurement can be effectively compensated, and rotations around all three axes on the Poincaré sphere can be realized. These results establish a practical APC architecture based on optical computing for photonics chips. The proposed APC methods, combined with a FPGA-based hardware acceleration, will enable high speed on-chip polarization controllers.
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All authors Xueying Ren, Meinan Guo, Xuyang Wang, Bailin Shen, Lingyan Zhang, Minyue Yang, Nannan Ning, Jiaxin Huang, Lv Lv, Jun Zou, Yongmin Li

Optics

High-Performance Photonic Crystal Biosensors using Sub-wavelength Nanopillars

Zhengzheng Zhai and Sajeev John

Photonic-crystal (PC) slabs composed of subwavelength silicon pillars erected on a thin silicon backing layer, with heights of only one or half lattice constant, are simulated for optical biosensing by numerical solution of Maxwell's equations. Localized optical cavity modes that form waveguides in the direction of biofluid flow, with quality factors surpassing \(10^4\), are embedded within the 2D photonic band gap of the 3D structure. Remarkable sensitivity to analyte binding is achieved using fragmented thin silicon pillars in regions of maximum localized optical-field intensity. Exceptional quality factors are realized through destructive wave interference of vertical radiation loss. This provides a rare combination of high sensitivity and low limit of detection in a device with minimal time requirement for analyte binding. The sensitivity to analyte binding is a frequency shift of nearly \(0.004\,[2\pi c/a]\) per analyte-thickness increment \(0.1a\). The sensitivity to background biofluid change is about \(4800\) nm per refractive index unit (RIU) for a specific lattice constant \(a = 5\,\mu\mathrm{m}\) using light of wavelength \(16.5\,\mu\mathrm{m}\).
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