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Physics Physics Optics

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Wednesday 26 August

Optics

Nanophotonic control of spatial information in scintillation detectors

Joshua Chen, Simo Pajovic, Seou Choi et al. (+9 more)

X-rays enable non-invasive imaging across medicine, security, materials science, and beyond, yet modern systems remain constrained by the need to resolve finer structures at lower radiation dose. Scintillators are the dominant materials for detecting X-rays, but face a longstanding compromise: thick scintillators absorb X-rays effectively, whereas optical photons generated throughout their volume spread before detection, degrading spatial information. Existing scintillator architectures largely try to preserve resolution by physically confining light using pixels, columnar crystals, or microstructured channels. Here, we show that high-resolution detection does not require the volumetric confinement of scintillation light. A metalens integrated directly with a bulk scintillator uses nanophotonic wavefront control to preferentially transfer high-spatial-frequency information from volumetrically generated scintillation light to the detector, while retaining the X-ray absorption of a thick scintillator. We experimentally recover fine spatial detail in X-ray images of inorganic and biological specimens. In a detector geometry relevant to computed tomography (CT), the experimentally validated model predicts a fivefold reduction in required X-ray dose and a 25-fold increase in resolution bandwidth relative to a state-of-the-art pixelated scintillator. These results establish wavefront engineering as a route to separating efficient X-ray absorption from optical image formation, with the potential for substantially higher-resolution, lower-dose CT.
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All authors Joshua Chen, Simo Pajovic, Seou Choi, Sachin Vaidya, William Michaels, Louis Martin-Monier, Christina M. Spägele, Steven E. Kooi, Juejun Hu, Rajiv Gupta, Charles Roques-Carmes, Marin Soljačić

Optics

Intrinsic Radial Landau Rainbow in Triaxial Strained Photonic Crystal

Guangti Lu and Satoshi Iwamoto

Localized resonances are essential for enhancing light matter interaction, controlling emission, and realizing compact optical resonators and lasers. Landau levels offer a distinct route to organizing photonic states through synthetic magnetic fields, but their high degeneracy does not define spectrally separated localized resonances. Here, we report the intrinsic lifting of degeneracy in photonic Landau levels in a triaxially strained photonic crystal, leading to the emergence of an intrinsic radial Landau rainbow. The triaxial deformation generates photonic Landau levels through a strain induced pseudomagnetic field, while an accompanying pseudoelectric field lifts the degeneracy of the Landau levels. As a result, each Landau level splits into an equally spaced frequency ladder of localized resonances. In zeroth Landau level, these modes exhibit intensity maxima that move progressively outward from the device center, establishing a radial frequency position mapping and Landau rainbow. Our results reveal an intrinsic fine structure of photonic Landau levels in a triaxial strained photonic crystal and provide a route to spatially ordered Landau level resonances.
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Tuesday 25 August

Optics · Cross-listed from quant-ph

Multipair-resilient entanglement swapping with complementary linear-optical measurements

Siavash Mirzaei Ghormish and Ryan M. Camacho

Multipair emission is a principal source of false heralds in entanglement swapping with spontaneous parametric down-conversion sources. A conventional Bell-state measurement (BSM) cannot distinguish the desired arrival of one photon from each neighboring source from a mixed-polarization double emission by one source accompanied by vacuum from the other. We show that a cascaded network can resolve this ambiguity by allowing its successive swapping stations to perform different measurements. A direct-basis BSM rejects same-polarization double emissions, whereas a balanced equatorial analyzer, implemented by a four-mode Green Machine (GM), uses two-photon interference to reject mixed-polarization double emissions. At the same time, it recovers same-polarization inter-source events rejected by the BSM as resolved $\phi$-type Bell heralds. Their rejection sets jointly cover both single-source two-photon classes while retaining contributions from both useful inter-source classes. We classify the passive four-mode, number-resolving analyzers satisfying this condition and identify the BSM and GM as canonical balanced representatives. Using a Gaussian-state analysis exact to all orders of multipair emission, we evaluate three-source BSM–GM and four-source BSM–GM–BSM Pure Bell Pair sources under coupling, detector, and channel loss. The three-source network suppresses the leading infidelity, while the four-source network heralds an exact Bell state in the lossless limit, a property that holds for every alternating BSM–GM chain with four or more sources. The fidelity advantage over source-count-matched all-BSM networks persists at every loss level studied, a single-channel rate advantage appears without multiplexing, and spectral multiplexing raises the Bell-pair delivery probability toward the asymptotically deterministic limit.
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Optics

First-Principles Prediction of Nonlinear Optical Response in TiO$_2$ for High-Power Dielectric Mirror Applications

Koya Shimaoka, Yusuke Kondo, Kazunori Shibata et al. (+1 more)

Dielectric multilayer mirrors are essential components in optical experiments using high-power lasers, where titanium dioxide (TiO$_2$) is widely employed as a high-refractive-index dielectric material. In this study, we investigate the nonlinear optical response of TiO$_2$ under intense ultrashort laser pulses using real-time first-principles electron-dynamics simulations based on time-dependent density functional theory (TDDFT). We reveal intensity-dependent absorption driven by multiphoton excitation and optically excited free carriers, and simulate the resulting electron-light coupled dynamics in TiO$_2$ nanofilms using a multiscale Maxwell-TDDFT framework. Direct evaluation of the reflected and transmitted fields shows reduced reflectance at high intensities ($I \sim 10^{13}$ W/cm$^2$), demonstrating a pronounced nonlinear optical response. Furthermore, the optical response properties are compared among various stable and metastable crystalline phases of TiO$_2$-rutile, anatase, brookite, TiO$_2$-II, and TiO$_2$-B-as well as an amorphous supercell model. These results provide microscopic insight into intensity-dependent optical degradation in TiO$_2$-based dielectric optical components exposed to intense femtosecond laser fields.
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All authors Koya Shimaoka, Yusuke Kondo, Kazunori Shibata, Mitsuharu Uemoto

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

Carrier-Resolved Attosecond Valley Polarimetry of Monolayer MoS$_2$

Navdeep Rana, Lun Yue and Mette B. Gaarde

In recent years, all-optical writing and switching of valley polarization in two-dimensional semiconductors has been demonstrated on femtosecond timescales. Reading this polarization out on the same timescale, carrier by carrier, has so far remained out of reach. Employing semiconductor Bloch equation simulations of monolayer MoS$_2$, we show that attosecond transient absorption closes this gap by turning the Mo $4p$ semicore edge into a quantitative valley polarimeter. We find that pump-enabled core-to-valence absorption probes the holes while core-to-conduction bleaching probes the electrons, so that a single spectrum identifies each carrier by its photoabsorption energy. The hole channel, Pauli-blocked in equilibrium, emerges background-free. Its circular dichroism reverses sign with the pump helicity, and its normalized magnitude is proportional to the valley polarization. Finally, we show that scanning the probe delay clocks the few-femtosecond write in real time. Thus, attosecond core-level dichroism is a carrier-sensitive, quantitative probe of the creation and evolution of valley polarization.
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Optics

Single-Mode Control of High-Speed and Low-Threshold III-V/Si Quantum Dot Microring Lasers via Azimuthal Gratings

Xucheng Yang, Yingtao Hu, Eunso Shin et al. (+9 more)

Hybrid III-V/silicon quantum-dot microring lasers are compact, energy-efficient O-band sources, but their whispering-gallery cavities are inherently multimode and bidirectional, producing unstable mode hopping that is incompatible with dense wavelength-division multiplexing. We show that an azimuthal grating patterned into the silicon ring - a single lithographic degree of freedom - converts this multimode cavity into a wavelength-addressed, single-mode source. A coupled-mode analysis derives the angular-momentum selection rule from first principles and shows that the inner-wall corrugation replaces the degenerate counter-propagating pair with symmetric and anti-symmetric standing-wave supermodes of unequal radiative loss. At the second-order Bragg condition the anti-symmetric mode is symmetry-protected, yielding a high-quality-factor state at exactly one azimuthal order; finite-element simulations confirm this and identify grating depth as the primary loss-engineering handle. Devices fabricated in-house on a 100 mm silicon-on-insulator platform hold a single longitudinal order with a side-mode suppression ratio of 37.9 dB and continuous, hop-free tuning, while the emission wavelength stays fixed across a factor-of-two change in cavity loading, set lithographically rather than by the gain peak. Because the grating decouples the lasing wavelength from the quantum-dot gain, the detuning becomes a mask-level design variable that sets the temperature of minimum threshold current, reaching 1.95 mA near 50 {\deg}C. Combined with side-mode suppression beyond 37 dB and multi-gigahertz direct modulation, these lasers are practical building blocks for cascaded, wavelength-addressed transmitter arrays in data communication and co-packaged optics.
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All authors Xucheng Yang, Yingtao Hu, Eunso Shin, Antoine Descos, Yatiraj Ramanujam, Bassem Tossoun, Yuan Yuan, Geza Kurczveil, Jonathan Wierer, Ray Beausoleil, Di Liang, Stanley Cheung

Optics · Cross-listed from cond-mat.str-el

High-harmonic fingerprints of sharp spin twists in a chiral soliton lattice

Atsushi Ono

A magnetic field applied perpendicular to the helical axis of a monoaxial chiral helimagnet compresses the spin helix into a coplanar chiral soliton lattice (CSL). We show that optically driven high-harmonic generation from itinerant electrons coupled to a frozen CSL resolves the lattice-scale structure of the localized twist, rather than the continuum soliton shape. High-order harmonics remain perturbative for the uniform helix. As the winding localizes at fixed magnetic period, they grow by many orders of magnitude and acquire a nonperturbative dependence on the drive amplitude. The growth originates from a spatially nonuniform effective hopping that turns each soliton into a localized dip in the hopping amplitude. When the degree of winding localization is held fixed, high-order intensities fall by many orders of magnitude as the magnetic period increases toward the continuum limit, where the hopping modulation is spatially smoothed. High-order harmonics thus resolve a real-space characteristic of the coplanar CSL, even in the absence of scalar chirality and an emergent magnetic field.
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Optics · Cross-listed from cond-mat.mtrl-sci

Predicting THz Generation Capability of Organic Crystals through Data Mining and Crystal Nonlinearity Models

Sin Hang Ho, Ashton Roma, Connor Barlow et al. (+5 more)

We report the use of DFT computation and mathematical models to predict the nonlinear dielectric polarization (P^{NL}) and nonlinear susceptibility coefficients (\chi^{(2)}_{IJK}) of organic materials based on their crystal structures. We apply this computation approach on single-component crystals, co-crystals and ionic crystals found through data mining the Cambridge Structural Database. We verify these computational results with experimental terahertz (THz) generation efficiencies for known THz generators, demonstrating consistency between the measurements and the computed values. Several mined structures show similar or larger PNL values compared to state-of-the-art THz generation crystals DAST, OH1 and BNA, suggesting great potential for their use in nonlinear optical (NLO) applications. Importantly, we also compared the resulting model of nonlinear optical tensor components with commonly-used simplifications of nonlinearity, showing that the comprehensive approach should be the standard method to evaluate the nonlinear optical properties of single-crystalline materials.
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All authors Sin Hang Ho, Ashton Roma, Connor Barlow, Matthew Lutz, Natalie Green, Stacey Smith, David Michaelis, Jeremy A Johnson

Optics

Effects of Quantum Noise and Source Blurring on Dark-Field Signal Retrieval in X-ray Speckle-Based Imaging

Hunwoo Lee, Jingcheng Yuan and Mini Das

X-ray speckle-based dark-field imaging offers high sensitivity to sub-pixel structural features, yet its quantitative reliability in clinical and preclinical settings remains constrained by low photon flux and finite focal spot sizes. However, how hardware-induced noise and source blurring propagate through retrieval algorithms to degrade signal integrity is not fully understood. Here, we systematically evaluate algorithm robustness quantified by signal linearity, sensitivity, and bias under photon starvation and source blurring across two mathematically distinct frameworks: differential-based intrinsic tracking (Low-Coherence System, LCS) and patch-wise explicit tracking (X-ray Speckle-Tracking Speckle-Vector-Tracking, XST-XSVT). Our experimental results demonstrate that input speckle pattern distortions propagate through retrieval algorithms in fundamentally different ways depending on algorithm architecture. As an example, using our setup, under severe photon starvation, derivative noise amplification in LCS causes its dark-field signal linearity and sensitivity to drop precipitously, while sharply elevating baseline bias. In contrast, XST-XSVT restricts these losses for sensitivity while maintaining a stable baseline, as its patch-wise variance calculation inherently suppresses stochastic noise. Similarly, under blur-limited conditions , source blurring washes out the speckle pattern, directly reducing dark-field sensitivity for both LCS and XST-XSVT. This characterization establishes operational boundaries for low-power and low-coherence X-ray systems, guiding algorithm selection and framework optimization to realize quantitative dark-field imaging in preclinical and clinical applications.
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Optics

Ultrafast tuning of the focusing efficiency of a nonlinear atomically thin lens

Rahil Rezwan, Bernardo Dias, Tom Hoekstra et al. (+10 more)

Control over light focusing is paramount for optical and imaging systems. However, its implementation in active and integrated nanophotonic devices is hindered by the bulky and static nature of standard lenses. Here, we show that Fresnel Zone Plate Lenses (FZPL) based on a monolayer Transitional Metal Dichalcogenide are a viable solution to the challenges of miniaturization, integration, and active control of the focusing efficiency, featuring both ultrafast and large modulation depth. Using a monolayer $WSe_2$ FZPL, we demonstrate all-optical ultrafast ($\sim$ ps) modulation of the focusing efficiency close to $\sim$30%, that we achieve by exploiting the nonlinear exciton-resonant enhancement and modulation of second harmonic generation.
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All authors Rahil Rezwan, Bernardo Dias, Tom Hoekstra, Mehmet At{\i}f Durmuş, Bauke van der Vorm, Till Weickhardt, Omid Ghaebi, Zhuoyuan Lu, Devapriyo Mithun, Carsten Ronning, Yuerui Lu, Jorik van de Groep, Giancarlo Soavi

Optics

Phase-controlled super-modes in a `lossy' tri-waveguide coupled micro-ring resonator system

Tianrui Li, Max Goodwin, Matthew P. Halsall et al. (+1 more)

In coupled micro-ring resonator (MRR) systems, the coupling process plays a critical role in determining the optical response, yet models of these structures typically assume this process to be either lossless, or dissipative with either purely real or purely imaginary coupling rate, respectively. Dissipative coupling is contingent on having appropriately phase engineered structures with intricate coupling geometries, but systems exhibiting `lossy coupling', i.e., characterized by complex-valued coupling rates, have received comparatively little attention. In this work, we investigate the effect of such `lossy' coupling, by modelling the optical response of a tri-waveguide coupled MRR system, using Temporal Coupled-Mode Theory (TCMT). The `lossy' coupling occurs via a common bus waveguide, positioned between a pair of MRRs, leading to the emergence of a pair of intrinsic resonances, whose frequency and linewidth may be tailored by controlling the respective coupling rates from either MRR. We develop these ideas, and by connecting the input (driving) waveguides, using a 3dB y-splitter, demonstrate a novel, coherently driven, lossy-coupled MRR, which exhibits either an absorptive or transparent resonance peak on demand by phase-controlled super-modes.
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All authors Tianrui Li, Max Goodwin, Matthew P. Halsall, Iain F. Crowe

Optics

AlGaAs nanowires as a universal platform for GaAs, InGaAs, and InAs quantum dots

Rohan Radhakrishnan, Rodion Reznik, Gilles Patriarche et al. (+5 more)

Optical quantum dots (QDs) are central to photonic quantum technologies, with fabrication approaches tailored to different spectral ranges. A key challenge, however, is the realization of a unified platform$\unicode{x2014}$a single growth method combined with a host material offering a designable architecture$\unicode{x2014}$enabling wavelength tunability across the full emission range and co-integration of multiple quantum dots. Here, we introduce AlGaAs nanowires as a universal host for GaAs, InGaAs, and InAs QDs. Building on our previous demonstration of high-quality GaAs QDs, we realize InGaAs QDs with tunable emission by varying the growth duration from 2 to 5 s, achieving emission at 780 and 920 nm. We further showcase the platform's versatility for multi-quantum-dot devices by co-integrating two InGaAs QDs, as well as GaAs and InGaAs QDs within a single nanowire. Finally, we initiate a first step toward pure InAs QDs by growing a pristine InAs segment on AlGaAs nanowires, demonstrating material compatibility.
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All authors Rohan Radhakrishnan, Rodion Reznik, Gilles Patriarche, Igor Ilkiv, Konstantin Kotlyar, Anna Andreeva, George Cirlin, Nika Akopian

Optics · Cross-listed from physics.chem-ph

Quantum Vibronic Dynamics Shape Catalytically Relevant Au-Ligand Interfaces in Atomically Precise Gold Nanoclusters

Mengyuan Cui, Tianrui Chen, Junhua Zhou et al. (+6 more)

Atomically precise gold nanoclusters are versatile for photocatalysis and energy conversion because their electronic structure stems from strong metal-ligand interactions. However, these interactions are mostly discussed statically, leaving dynamic reorganization of Au-ligand interfaces under photoexcitation unclear. We investigate rod-shaped [Au25(PPh3)10(SC2H5)5Cl2]2+ using ultrafast transient-grating spectroscopy, two-dimensional electronic spectroscopy, ab initio calculations, and hierarchical equations-of-motion simulations. The multidimensional spectra resolve multiple electronic relaxation pathways and a hierarchy of coherent structural motions, from localized Au-ligand distortions to collective framework vibrations. Wavelet analysis reveals that high-frequency Au-ligand vibrations emerge immediately after excitation, whereas low-frequency collective modes appear later through interstate vibronic coupling, indicating sequential redistribution of structural coherence. Simulations reproduce the nonlinear response and identify the microscopic vibronic couplings responsible. The results show that photoexcitation drives continuous ultrafast reorganization of the Au-ligand bonding network, transiently reshaping interfacial electronic structure before thermalization. This work establishes dynamic Au-ligand interfaces as the microscopic link between excited-state energy flow and photochemical function in atomically precise nanoclusters.
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All authors Mengyuan Cui, Tianrui Chen, Junhua Zhou, Xiangmei Duan, Vandana Tiwari, Chao Mei, Ajay Jha, Fulu Zheng, Hong-Guang Duan

Optics

Nonlocal-nonlinear phonon polaritons

Gonzalo Álvarez-Pérez, Line Jelver, Alexander Paarmann et al. (+1 more)

When light is confined to deeply subwavelength volumes, optical responses can become nonlocal. Yet how nonlocality reshapes nonlinear light-matter interactions remains largely unexplored, particularly in dielectrics. Here, we theoretically uncover a new class of nonlinear optical processes arising from the interplay between optical-phonon propagation and ionic-bond anharmonicity in polar crystals. We show that, unlike conventional local nonlinearities, this mechanism enables second-order responses even in centrosymmetric materials. Moreover, these responses can be tuned by the confinement and resonantly enhanced near optical-phonon resonances. Using density functional perturbation theory, we quantify the resulting nonlocal second-order susceptibilities in representative polar crystals. Our results establish nonlocal-nonlinear optics as a new regime of light-matter interaction in dielectrics.
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All authors Gonzalo Álvarez-Pérez, Line Jelver, Alexander Paarmann, Simone De Liberato

Optics · Cross-listed from astro-ph.IM

Quantum-optimal instruments for high-contrast imaging with multi-plane light converters

Sebastiaan Y. Haffert, Yinzi Xin and Rico Landman

Spatial Mode Demultiplexers (SPADE) are devices that split an incoming wavefront into a particular set of electric field modes. SPADEs have been shown to be quantum-optimal for many measurement problems including coronagraphy, wavefront sensing and interferometric (nulling) beam combiners. We will show how quantum optimal SPADEs can be implemented using Multi Plane Light Converters (MPLC). MPLCs are devices that use several phase plates in sequence to achieve arbitrary unitary transformations. The phase plates themselves are implemented using liquid-crystal technology that allows us to create high-quality broadband phase plates. The accurate control of the local phase through the direct write method results in MPLCs with minimal background scatter. We will show the designs and simulated performance for each of the proposed use cases for the ELTs, HWO and LIFE and show how they improve over current concepts.
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Optics

Metalens stereoscopic optical palpation for imaging cancer mechanics

Haoyi Yu, Rhys Jones, Chi Li et al. (+13 more)

Accurate intraoperative margin assessment is critical for complete resection of solid tumours. However, surgeons routinely rely on manual palpation, which is highly subjective and fundamentally limited by poor spatial resolution, and pre-operative imaging lacks real-time feedback. While emerging optical elastography techniques offer quantitative mechanical contrast, their reliance on bulky optical components necessitates cumbersome alignment and hinders integration into miniaturised surgical instruments. Here, we report metalens stereoscopic optical palpation (MSOP), a nanophotonic imaging platform leveraging a binocular metalens integrated with a single CMOS sensor to achieve high-fidelity, self-aligned elastography. By replacing complex bulk optics with a compact stereoscopic architecture, MSOP enables robust, high-contrast mapping of tissue surface stress. Following validation in heterogeneous silicone phantoms, we demonstrate MSOP's translational potential by characterising the mechanical signatures of malignancies in fresh mouse pancreatic cancer models, as well as excised human breast and liver specimens. By providing reliable, label-free mechanical contrast across diverse oncological landscapes, MSOP offers a compact tool for precise intraoperative margin delineation to reduce re-excision rates and improve surgical outcomes.
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All authors Haoyi Yu, Rhys Jones, Chi Li, Bo He, Renate Zilkens, Louise N. Winteringham, Laura Gale, Mireille Hardie, Fiona Bellamy, Saud Hamza, Christobel M. Saunders, Liver Cancer Collaborative, Stefan A. Maier, Brendan F. Kennedy, Haoran Ren, Qi Fang

Optics

Design and numerical performance analysis of efficient Ag3TaX4 (X = S, Se, Te) thin film solar cells

Md. Nahid Hasan, Tanvir Ahmed, Md. Abdur Rashid et al. (+3 more)

Silver-based ternary chalcogenides have recently emerged as promising absorber materials for thin film photovoltaics. Nevertheless, their photovoltaic performance in complete device architectures has not yet been systematically explored. In this work, three-dimensional (3D) n-CdS/p-Ag3TaX4 (X = S, Se, Te)/p+-GeS thin-film solar cells have been designed and numerically investigated using the Semiconductor Module of COMSOL Multiphysics. Herein, the various performance matrices of the proposed devices have been analysed in accordance with the changing of depth, carrier, and defect concentration in each layer of the structures. The optimized Ag3TaS4-based device delivers a power conversion efficiency, PCE of 24.66%, open circuit voltage, VOC of 1.4V, short circuit current density, JSC of 20.68 mA/cm2, and fill factor, FF of 85.16%. The Ag3TaSe4-based solar cell exhibits the PCE of 28.1% with VOC = 1.19V, JSC = 27.0 mA/cm2, and FF = 87.44%. The Ag3TaTe4 solar device shows a PCE of 27.56% with a VOC of 0.88 V, JSC of 36.14 mA/cm2, fill factor of 86.65%. These results provide a deeper insight into device operation and offer practical design guidelines for fabricating efficient Ag3TaX4 (X = S, Se, T e)-based novel next-generation solar cells.
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All authors Md. Nahid Hasan, Tanvir Ahmed, Md. Abdur Rashid, Tanzina Rahman, Dinesh Pathak, Jaker Hossain

Optics

An Ab initio Framework for Simulating Ultrafast Nonlinear Cavity Quantum Electrodynamics Spectra

Luis Vasquez, Kewei Sun, Haibo Ma et al. (+1 more)

In this letter we introduce a theoretical framework for the simulation of ultrafast transient absorption pump-probe spectra of molecular polaritons. We derive and implement the cavity quantum electrodynamics (QED) evolution equations of polaritonic states within the framework of the quasi-classical doorway-Window pproximation, hereto referred cQUEDA /sikeda/. This framework uses outputs from mixed quantum-classical dynamics simulations in the absence of the cavity. Then by including cavity parameters accounting for cavity rate loss, coupling strength, and frequency detuning, we simulate transient absorption pump-probe spectra. Consequently, we address one of the main standing problems of cavity QED, the simulation of polaritons ultrafast dynamics and nonlinear optical properties. We demonstrate the performance of our method by computing the ground-state bleach (GSB), stimulated emission (SE), and excited-state absorption (ESA) contributions of transient absorption pump-probe spectra of pyrazine strongly coupled to a cavity. The cQUEDA is an on-the-fly computationally efficient framework with low computer requirements: the pyrazine calculations, for example, took minutes on modern laptops. cQUEDA offers wide-ranging applicability and can be generalized to model diverse nonlinear spectroscopic signals and quantum optics responses.
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All authors Luis Vasquez, Kewei Sun, Haibo Ma, Maxim F. Gelin

Optics

Mesa Orientation Engineering for Polarization Locking in VCSELs

Zifeng Yuan, Wenkai Shan, Tingting Chen et al. (+2 more)

While polarization stability is common in many optical systems, intentional polarization bi-stability is also important for polarization-encoded computing. We propose a mesa orientation strategy to engineer the polarization switching of vertical-cavity surface-emitting lasers (VCSELs). Further experiments demonstrate improved polarization locking performance.
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All authors Zifeng Yuan, Wenkai Shan, Tingting Chen, Beibei Lin, Aaron Danner

Monday 24 August

Optics

Coverage-information uncertainty for single-helicity light

Hyoseok Park

A circularly polarized far field must be dark somewhere: its amplitude is a section of a twisted line bundle. We prove this exacts a joint coverage-rate cost that cannot vanish faster than the inverse fourth power of the mode order, and we construct an explicit family of fields attaining that exponent. At lowest order the global optimum is the spin-1 anticoherent state, independently known as optimal for rotations about an unknown axis. The same floor caps photon collection in single-helicity quantum links; the opposite helicity removes it at a cost set by the inverse mode count.
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Optics · Cross-listed from cond-mat.mes-hall

Quantum encoding of structured light into in-plane topological spin textures

Pavel A. Vorobyev, Daichi Kurebayashi and Oleg A. Tretiakov

Structured light offers a powerful means of controlling light-matter interactions through multiple tunable optical degrees of freedom. Using micromagnetic simulations, we investigate the nucleation of asymmetric bimerons and antibimerons by pulsed Laguerre-Gaussian optical vortices in chiral ferromagnetic thin films with $C_{nv}$ and $D_{2d}$ symmetries, respectively. For optical vortices with orbital angular momentum (OAM) $|m|=1$, circularly polarized beams deterministically nucleate a single bimeron or antibimeron via the interplay of spin angular momentum, OAM, and magnetic chirality, whereas linearly polarized beams produce textures whose topological charge directly follows the OAM ($Q=m$). Optical vortices with OAM $|m|>1$ nucleate clusters and other configurations composed of multiple spin textures, whose morphology and topological charge depend sensitively on the optical quantum numbers and pulse parameters. These findings reveal a route to topology-selective writing through the encoding of optical quantum numbers into distinct in-plane topological magnetic states.
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Optics

Classification of Non-Hermitian Flat Bands

Chang-geun Oh and Jun-Won Rhim

Exact flat bands provide a versatile setting for correlated and topological phenomena, yet their properties are controlled not only by their dispersion but also by the structure of their Bloch projectors. Here, we establish a projector-based classification of non-Hermitian flat bands. In contrast to Hermitian flat bands, non-Hermiticity introduces a biorthogonal projector whose left-right pairing permits a distinct norm-pole singularity. We identify four classes: analytic NH-A, continuous but nonanalytic NH-C, bounded but discontinuous NH-D, and pole-singular NH-E. We show that continuity of the biorthogonal projector preserves the locking of the right, left, and biorthogonal Chern numbers, $C_R=C_L=C_{\rm bi}$, thereby realizing non-Hermitian critical topological flat bands. Once continuity is lost, this locking can break down; in particular, a mismatch $C_R\neq C_L$ can occur in the NH-E class. Finally, we show that this Chern number mismatch ensures to produce an anomalous enhancement of resonant cross-orbital transfer. Our results establish biorthogonal projector regularity as the organizing principle linking compact localized states, topology, and driven response in non-Hermitian flat bands.
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Optics · Cross-listed from quant-ph

Sustained macroscopic quantum coherence in a superradiant solid under ambient conditions

Wei-Jiang Wu, Da-Wu Xiao, Wen-Tao Wang et al. (+5 more)

Macroscopic quantum coherence, such as in laser, Bose-Einstein condensates, superfluids, and superconductors, is important to fundamental physics and useful for quantum technologies. Superradiance provides a mechanism to produce coherence among a large number of particles and photons. Its implementation, however, has been limited to gaseous systems, solids at very low temperature, or short pulses. Here we demonstrate a solid-state superradiant maser under ambient conditions, which establishes long-lived coherence among about $10^{14}$ nitrogen-vacancy center spins in diamond and about $10^9$ photons in a microwave cavity. By varying the system parameters to access the above-threshold, well-above-threshold, and deep-above-threshold regimes, we observed continuous-wave masing, periodic amplitude modulation, and sequences of superradiant bursts, which are attributed, correspondingly, to macroscopic spin coherence synchronized at a fixed frequency, a coherent time crystal of large spins, and unsynchronized superradiant transients. This work demonstrates that macroscopic quantum coherence can be spontaneously generated and maintained in solids under ambient conditions and provides a solid-state platform for exploring bright quantum lights with many-body correlations.
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All authors Wei-Jiang Wu, Da-Wu Xiao, Wen-Tao Wang, Xin-Yu Chen, Xian-Feng Wang, Ming-Zhong Ai, Quan Li, Ren-Bao Liu

Optics

Collective Topological Dark Solitons, Platicons, and Bright-Like Solitons in Normal Dispersion Optical Frequency Combs

Seyed Danial Hashemi, Ankitkumar Maisuriya and Sunil Mittal

Bright dissipative Kerr solitons generated in anomalous-dispersion microresonators underpin integrated optical frequency combs that have enabled applications including precision metrology, spectroscopy, coherent communications, and optical frequency synthesis. In contrast, Kerr resonators operating in the normal-dispersion regime can support dark solitons and platicons, but even the initiation of frequency comb generation typically requires auxiliary mechanisms, such as avoided mode crossings or pulsed pumping, to satisfy the phase-matching condition for four-wave mixing. Here we show that topological edge states in two-dimensional Kerr resonator lattices intrinsically satisfy this phase-matching condition, enabling the generation of optical frequency combs and novel coherent dissipative structures in the normal-dispersion regime without any auxiliary mechanisms. The resulting frequency combs self-organize into collective dark solitons that exhibit large-scale spatiotemporal synchronization across multiple resonators at the entire lattice edge. By tuning the pump detuning, we demonstrate the continuous evolution of topological dark solitons into topological platicons while preserving collective synchronization. Remarkably, we show that the topological lattice also supports collective bright-like soliton states despite all constituent resonators operating in the normal-dispersion regime. Our results establish topological Kerr resonator arrays as a versatile route for engineering a broad family of coherent dissipative structures, ranging from dark solitons to bright-like soliton states, within a single platform. They also provide a route toward integrated frequency-comb generation in material platforms and wavelength ranges where normal material dispersion has traditionally constrained comb generation in conventional single-resonator systems.
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Optics

Diffractive optical element for super-Gaussian beam shaping on intersatellite optical communications

Mario Badás Aldecocea, Ziheng Wang, Mohammad Dabiri et al. (+1 more)

Pointing jitter can significantly degrade the performance of intersatellite optical communication links. This work investigates diffractive optical beam shaping as a means of generating super-Gaussian profiles with reduced sensitivity to transmitter misalignment. Phase screens are designed using a Gerchberg–Saxton phase-retrieval algorithm and evaluated for different super-Gaussian orders. Lower-order profiles are reproduced accurately, whereas higher orders are increasingly limited by numerical discretization and finite-aperture effects. The practical implementation of the phase screens using fused-silica diffractive optical elements is assessed through sensitivity analyses of radial manufacturing resolution, phase quantization, phase-depth errors, and incident-beam wavefront aberrations. The results provide manufacturing tolerances and wavefront-quality requirements for preserving the desired beam shape.
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All authors Mario Badás Aldecocea, Ziheng Wang, Mohammad Dabiri, Iman Tavakkolnia

Optics

Nonlocality is the missing design rule for topological photonics

Fatemeh Davoodi

Topological photonics has provided powerful design rules for routing and localizing light through geometry, symmetry and engineered coupling. However, fabricated nanophotonic and plasmonic devices rarely realize only the local or short-range interaction networks assumed in compact topological models. Long-range near-field coupling, retardation, radiation leakage, substrate-assisted hybridization, material dispersion and fabrication disorder can reshape the optical modes that are interpreted as topological. In this Perspective, I argue that nonlocality should be treated as a design parameter rather than as a residual perturbation. This shift requires moving from ideal phase labels toward calibrated interaction models, finite-structure observables, robustness maps and graded confidence measures. I discuss how full-wave simulations, experiments and physics-informed learning can connect geometric design variables to effective electromagnetic interaction networks. Such calibrated workflows can clarify when a topological design rule is reliable, when it fails, and how nonlocal coupling can be exploited for robust nanophotonic devices.
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Optics · Cross-listed from q-bio.OT

Beyond chlorophyll: machine learning estimates of diagnostic phytoplankton pigments from multispectral ocean colour data

David Moffat, Angus Laurenson, Victor Martinez-Vicente et al. (+4 more)

Phytoplankton play a central role in marine ecosystems and the global carbon cycle, with different groups contributing differently to ocean biogeochemical processes. While standard techniques exist for monitoring phytoplankton concentration from ocean-colour data, their community composition remains difficult to observe at large scales. Chlorophyll-a, widely available from satellite ocean-colour observations, is commonly used as a measure of phytoplankton biomass but provides limited information on taxonomic composition. Accessory pigments, some of which are diagnostic of important phytoplankton groups, offer additional information on community structure, but their retrieval from ocean-colour data is challenging because of limited spectral resolution and strong covariance with chlorophyll-a. In this study, we evaluate machine learning methods for estimating diagnostic pigment concentrations from multispectral satellite observations. Using a global dataset of 33,640 High Performance Liquid Chromatography (HPLC) measurements matched with ESA Ocean Colour Climate Change Initiative (OC-CCI) reflectance data, we compare Random Forest and TabPFN models trained on multispectral reflectance with baseline models using chlorophyll-a alone. A temporally stratified validation scheme is employed to reduce the effects of autocorrelation. Results show that multispectral models consistently outperform approaches based solely on satellite-derived chlorophyll-a, demonstrating that ocean-colour reflectance contains additional information relevant to pigment discrimination. Improvements vary by pigment, with those strongly correlated with chlorophyll-a showing limited gains, while others exhibit substantial improvement. These findings highlight the potential of machine learning to extract ecologically relevant information from satellite data beyond conventional chlorophyll-based approaches.
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All authors David Moffat, Angus Laurenson, Victor Martinez-Vicente, Gemma Kulk, Xuerong Sun, Robert J. W. Brewin, Shubha Sathyendranath

Optics · Cross-listed from physics.chem-ph

Tracking molecular hydrogen formation from ionized water in real time

Chuan Cheng, Chi-Hong Yuen, Eleanor Weckwerth et al. (+8 more)

Removing an electron from a water molecule can drive its two hydrogen atoms to pair up and depart as molecular hydrogen. However, even for this elementary reaction, the route from start to finish has remained hidden because measurements have yet to follow the electronic and nuclear motion simultaneously. Combining correlated photoelectron and ion imaging, few-femtosecond pump–probe measurements, and nonadiabatic simulations, we track the complete pathway in isolated heavy water (D$_2$O) molecules. The reaction takes an indirect route and dissociates along three distinct pathways (direct, roaming, and delayed) with formation times of about 34 and 72 femtoseconds for the direct and delayed branches. Yet bond formation requires the molecule to first break its own symmetry. Only random asymmetric motion enables the electronic-state switch at a conical intersection, joining the two hydrogen atoms before the oxygen–hydrogen bond breaks. These results establish a time-resolved picture of molecular hydrogen formation from water and provide a general strategy for linking electronic excitation to chemical outcomes in settings from radiation damage to hydrogen production.
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All authors Chuan Cheng, Chi-Hong Yuen, Eleanor Weckwerth, Ian Gabalski, Aaron M. Ghrist, Haoran Ma, Andrew J. Howard, Mathew Britton, Yunquan Liu, Eric Wells, Philip H. Bucksbaum

Optics

Revealing Hidden Orbital Pathways in NonThermal Hot Carrier Relaxation of MXenes via NonSecular Redfield Quantum Kinetics

Ali Asghar Molavi Choobini, Abbas Chimeh and Jinhui Zhong

Non-thermal carrier relaxation is routinely inferred from population dynamics or spectroscopic observables, yet neither class of quantity uniquely identifies the microscopic channels through which energy and coherence are redistributed. We introduce a pathway-resolved quantum-kinetic framework that simultaneously projects ultrafast relaxation onto orbital populations, directional inter-orbital transferes, coherence, spectroscopic visibility, and a hidden-pathway sector of the dynamical transfer network. Application to MXenes exposes strongly non-uniform orbital redistribution together with material-specific hierarchies of microscopic transfer channels. Temperature, excitation amplitude, and dissipative parameters modulate pathway competition and spectral amplitudes while leaving the identity of the dominant channels largely intact. Instantaneous transfer contributions, cumulative directional transfer, coherence, and spectroscopic visibility are shown to follow inequivalent hierarchical orderings. This non-equivalence isolates a set of hidden pathways that remain dynamically consequential despite weak conventional spectroscopic signatures. The resulting time energy coherence representation recasts nonthermal relaxation as a structured dynamical network comprising observable and hidden sectors, thereby providing a general methodology for resolving microscopic orbital transfer pathways in driven quantum materials.
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Optics

Quantum Hydrodynamic Framework of Coherent Terahertz Emission in MXenes Driven via Engineered Femtosecond Waveforms

Ali Asghar Molavi Choobini, Abbas Chimeh and Jinhui Zhong

Coherent terahertz (THz) emitters based on low dimensional quantum materials have attracted significant interest for compact broadband photonic technologies. However, theoretical descriptions that consistently connect microscopic quantum dynamics to emitted THz radiation remain limited for MXenes, whose electronic properties are governed by transition metal d orbitals and chemically tunable surface terminations. A multiscale density-matrix formalism for coherent THz generation in metallic MXenes driven by engineered three color femtosecond waveforms is developed. Material-specific electronic structures are described by parameterized multiband tight binding Hamiltonians, while ultrafast carrier dynamics are treated using a non-secular Redfield master equation that explicitly retains interband coherence, carrier populations, electron phonon interactions, impurity scattering, and environment-induced relaxation. The transient photocurrent is explicitly decomposed into population and coherence driven contributions and linked to the emitted THz field through its time derivative, establishing a direct connection between microscopic quantum dynamics and macroscopic radiation. The results show that environmental coupling does not merely attenuate THz emission, but redistributes coherent and population currents and reshapes the emitted waveform in both the time and frequency domains. Systematic investigations of optical waveform parameters, effective electronic structure, and open system relaxation identify physically grounded strategies for enhancing broadband THz generation. The proposed methodology establishes a transferable microscopic design platform for connecting material specific electronic structure, quantum coherence, open system relaxation, nonlinear carrier transport, and coherent THz emission across MXenes and related low dimensional quantum materials.
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