Showing 1–26 of 26 results for author: Liang, M

Multi-quantum-channel mediated tunable single-photon skyrmions from metasurfaces

Authors: Yan Wang, Zhenyu Guo, Minggui Liang, Shuangchun Wen, Yijie Shen, Hailu Luo

Abstract: Quantum optical skyrmions, as topologically robust quantum information carriers, hold transformative potential for resilient high-dimensional quantum information networks. However, their practical exploitation was still restricted to a single quantum channel, which precludes the multiplexing essential for practical high-capacity quantum networks. Here, we utilize a metasurface to achieve multi-cha… ▽ More Quantum optical skyrmions, as topologically robust quantum information carriers, hold transformative potential for resilient high-dimensional quantum information networks. However, their practical exploitation was still restricted to a single quantum channel, which precludes the multiplexing essential for practical high-capacity quantum networks. Here, we utilize a metasurface to achieve multi-channel quantum state distribution of the polarization-entangled photon pairs, inducing a two-photon bunching effect in both the spin and spatial dimensions with compact flat optics. At the spatial bunching port, controlled manipulation of the spin-orbit interaction enables the generation of a tunable single-photon skyrmion pair. In contrast to any prior skyrmion generation, the single-photon skyrmions are mediated and topologically controlled by quantum measurement in multiple channels. Concurrently, during the amplitude and phase modulation process, both the skyrmion localization and the texture helicity can be precisely customized. The proposed tunable single-photon skyromions offer multidimensional controllability and topological stability provide a viable path toward noise-resilient high-dimensional quantum information processing. △ Less

Submitted 14 August, 2026; originally announced August 2026.

CLARE: Classification-based Regression for Electron Temperature Prediction

Authors: Michael Liang, Blake DeHaas, Naomi Maruyama, Xiangning Chu, Takumi Abe, Koh-Ichiro Oyama

Abstract: Electron temperature (Te) is an important parameter governing space weather in the upper atmosphere, but has historically been underexplored in the space weather machine learning literature. We present CLARE, a machine learning model for predicting electron temperature in the Earth's plasmasphere trained on AKEBONO (EXOS-D) satellite measurements as well as solar and geomagnetic indices. CLARE use… ▽ More Electron temperature (Te) is an important parameter governing space weather in the upper atmosphere, but has historically been underexplored in the space weather machine learning literature. We present CLARE, a machine learning model for predicting electron temperature in the Earth's plasmasphere trained on AKEBONO (EXOS-D) satellite measurements as well as solar and geomagnetic indices. CLARE uses a classification-based regression architecture that transforms the continuous Te output space into 150 discrete classification intervals. Training the model on a classification task improves prediction accuracy by 6.46% relative compared to a traditional regression model while also outputting uncertainty estimation information on its predictions. On a held out test set from the AKEBONO data, the model's Te predictions achieve 69.67% accuracy within 10% of the ground truth and 46.17% on a known geomagnetic storm period from January 30th to February 7th, 1991. We show that machine learning can be used to produce high-accuracy Te models on publicly available data. △ Less

Submitted 12 March, 2026; originally announced March 2026.

Comments: 19 pages, 8 figures. Submitted to JGR: Machine Learning and Computation. Research conducted at CU Boulder LASP with support from NASA and JAXA

Toroidal helical pulses

Authors: Shuai Shi, Hongcheng Zhou, Junjie Shao, Pan Tang, Bing-Zhong Wang, Mu-Sheng Liang, Yanhe Lyu, Boris A. Malomed, Yijie Shen, Ren Wang

Abstract: Toroidal topologies and helicity are pervasive in nature and hold basic importance in scientific research. In particular, the interplay between these features gives rise to fascinating toroidal helical electromagnetic excitations. Here, we present a theoretical framework and experimental realization to introduce a family of toroidal helical pulses, exploring the intersection of the helicity and pr… ▽ More Toroidal topologies and helicity are pervasive in nature and hold basic importance in scientific research. In particular, the interplay between these features gives rise to fascinating toroidal helical electromagnetic excitations. Here, we present a theoretical framework and experimental realization to introduce a family of toroidal helical pulses, exploring the intersection of the helicity and propagating toroidal modes. For this purpose, we propose a configuration combining a coaxial horn emitter and an equiangular spiral grating to directly generate such single-cycle pulses. In addition to their inherent non-transverse toroidal topology and space-time nonseparability, such pulses also possess controllable helicity. This work gives rise to a helical version of propagating toroidal electrodynamics, thereby paving the way for advanced applications, such as nontrivial light-matter interactions and data transfer. △ Less

Submitted 14 May, 2026; v1 submitted 10 March, 2026; originally announced March 2026.

Comments: To be published in Communications Physics

Fluorescence intensity correlations enable 3D imaging without sample rotations

Authors: Robert G. Radloff, Felix F. Zimmermann, Siqi Li, Stephan Kuschel, Anatoli Ulmer, Yanwen Sun, Takahiro Sato, Peihao Sun, Johann Haber, Diling Zhu, Miklós Tegze, Gyula Faigel, Matthew R. Ware, Jordan T. O'Neal, Jumpei Yamada, Taito Osaka, Robert Zierold, Carina Hedrich, Dimitrios Kazazis, Yasin Ekinci, Makina Yabashi, Ichiro Inoue, Andrew Aquila, Meng Liang, Agostino Marinelli , et al. (1 additional authors not shown)

Abstract: Lensless X-ray imaging provides element-specific nanoscale insights into thick samples beyond the reach of conventional light and electron microscopy. Coherent diffraction imaging (CDI) methods, such as ptychographic tomography, can recover three-dimensional (3D) nanoscale structures but require extensive sample rotation, adding complexity to experiments. X-ray elastic-scattering patterns from a s… ▽ More Lensless X-ray imaging provides element-specific nanoscale insights into thick samples beyond the reach of conventional light and electron microscopy. Coherent diffraction imaging (CDI) methods, such as ptychographic tomography, can recover three-dimensional (3D) nanoscale structures but require extensive sample rotation, adding complexity to experiments. X-ray elastic-scattering patterns from a single sample orientation are highly directional and provide limited 3D information about the structure. In contrast to X-ray elastic scattering, X-ray fluorescence is emitted mostly isotropically. However, first-order spatial coherence has traditionally limited nanoscale fluorescence imaging to single-crystalline samples. Here, we demonstrate that intensity correlations of X-ray fluorescence excited by ultrashort X-ray pulses contain 3D structural information of non-periodic, stationary objects. In our experiment, we illuminated a vanadium foil within a sub-200 nm X-ray laser beam focus. Without changing the sample orientation, we recorded 16 distinct specimen projections using detector regions covering different photon incidence angles relative to the X-ray free-electron laser (FEL) beam. The projections varied systematically as the fluorescing volume was translated along an astigmatism, confirming that FEL-induced fluorescence reflects real-space structural changes. Our results establish a new approach for lensless 3D imaging of non-periodic specimens using fluorescence intensity correlations, with broad implications for materials science, chemistry, and nanotechnology. △ Less

Submitted 29 October, 2025; v1 submitted 28 October, 2025; originally announced October 2025.

Validation of ERMES 20.0 finite element code for MAST Upgrade O-X mode conversion

Authors: Ruben Otin, Ying Hao Matthew Liang, Thomas Wilson, Simon Freethy, Valerian Hall-Chen

Abstract: This study presents the validation of the frequency-domain finite element code ERMES 20.0, benchmarked against Finite Difference Time Domain (FDTD) solvers. The simulations focus on Ordinary-Extraordinary (O-X) mode conversion in the Electron Bernstein Wave (EBW) regime of the MAST Upgrade experiment. Validation is performed in terms of mode conversion efficiency and wave propagation characteristi… ▽ More This study presents the validation of the frequency-domain finite element code ERMES 20.0, benchmarked against Finite Difference Time Domain (FDTD) solvers. The simulations focus on Ordinary-Extraordinary (O-X) mode conversion in the Electron Bernstein Wave (EBW) regime of the MAST Upgrade experiment. Validation is performed in terms of mode conversion efficiency and wave propagation characteristics. Several finite element formulations are tested and compared with the FDTD results. The simulations demonstrate excellent agreement between the different approaches, confirming the accuracy and robustness of ERMES 20.0 for modeling cold plasma wave interactions. △ Less

Submitted 30 September, 2025; originally announced September 2025.

A Doppler backscattering diagnostic for the EXL-50U spherical tokamak: plasma considerations and preliminary quasioptical design

Authors: Ying Hao Matthew Liang, Valerian Hongjie Hall-Chen, Terry L. Rhodes, Yumin Wang, Yihang Zhao

Abstract: The EXL-50U spherical tokamak was built by Energy iNNovation to develop technologies for proton-boron fusion in spherical tokamaks (Liu et al., Phys. Plasmas 2024). We present a conceptual design of the Doppler backscattering (DBS) diagnostic for the EXL-50U spherical tokamak. DBS is a diagnostic capable of measuring plasma turbulence, which is especially important for transport in tokamaks. Start… ▽ More The EXL-50U spherical tokamak was built by Energy iNNovation to develop technologies for proton-boron fusion in spherical tokamaks (Liu et al., Phys. Plasmas 2024). We present a conceptual design of the Doppler backscattering (DBS) diagnostic for the EXL-50U spherical tokamak. DBS is a diagnostic capable of measuring plasma turbulence, which is especially important for transport in tokamaks. Starting from a set of physical design constraints, such as port window availability and in-vessel space, we used SCOTTY (Hall-Chen et al., PPCF 2022), an in-house beam tracing code, to predict the location of the cutoffs and the corresponding scattering wavenumbers for several EXL-50U plasma scenarios. We find that we are able to measure scattering locations of 0.15 $<$ $ρ$ $<$ 1, with corresponding turbulent wavenumbers of 2.47 cm$^{-1}$$<$ $k_{\perp}$ $<$ 9.49 cm$^{-1}$. Here, $ρ$ is the normalised radial coordinate of the scattering location, and $k_{\perp}$ is the corresponding turbulent wavenumber. We then determine the optimal toroidal launch angles to ensure that the probe beam's wavevector is perpendicular to the magnetic field at the cutoff location, thereby maximising the backscattered signal. This matching is crucial due to the EXL-50U's high magnetic pitch angle, $\sim35^{\circ}$ at the outboard midplane. Given our results, we propose the use of toroidal steering and tunable frequency channels to ensure beams are well-matched with the magnetic pitch angle. We propose a quasioptical system that covers the U-band range (40--60 GHz). △ Less

Submitted 19 April, 2026; v1 submitted 22 September, 2025; originally announced September 2025.

Journal ref: Fusion Engineering and Design, Volume 228, July 2026, 115770

Robust Circularly Polarized Luminescence via Quasi-Bound States in the Continuum in Intrinsic Chiral Silicon Metasurfaces

Authors: Xiao-ke Zhu, Yu-Chen Wei, Jose L. Pura, Matthijs Berghuis, Minpeng Liang, Beatriz Castillo López de Larrinzar, Shunsuke Murai, Antonio García-Martín, José A. Sánchez-Gil, Sailing He, Jaime Gómez Rivas

Abstract: We demonstrate a circularly polarized photoluminescence emission, with dissymmetry factors $g_\mathrm{PL}$ over 0.1, from achiral organic dye molecules by leveraging quasi-bound states in the continuum (quasi-BICs) and surface lattice resonances (SLRs) in intrinsic silicon chiral metasurfaces. We find that the $g_\mathrm{PL}$ associated with the quasi-BIC mode remains robust against variations in… ▽ More We demonstrate a circularly polarized photoluminescence emission, with dissymmetry factors $g_\mathrm{PL}$ over 0.1, from achiral organic dye molecules by leveraging quasi-bound states in the continuum (quasi-BICs) and surface lattice resonances (SLRs) in intrinsic silicon chiral metasurfaces. We find that the $g_\mathrm{PL}$ associated with the quasi-BIC mode remains robust against variations in emission angle and dye thickness owing to its strong lateral field confinement. In contrast, the $g_\mathrm{PL}$ of the SLR mode exhibits sign inversion depending on the emission energy and dye layer thickness. The experimental results are supported by mode decomposition analysis, helicity density analysis, and near-field spatial distribution of the electric field. These findings illustrate the relevance of the emitter's layer thickness in optimizing the emission of circularly polarized light. They also elaborate on the robustness of chiral quasi-BICs, offering insights into chiral light-matter interactions and advancing the design of circularly polarized light-emitting devices. △ Less

Submitted 26 August, 2025; originally announced August 2025.

Toward Efficient and Accurate EMRI Parameter Estimation: A Machine Learning-Enhanced MCMC Framework

Authors: Bo Liang, Chang Liu, Hanlin Song, Zhenwei Lyu, Minghui Du, Peng Xu, Ziren Luo, Sensen He, Haohao Gu, Tianyu Zhao, Manjia Liang, Yuxiang Xu, Li-e Qiang, Mingming Sun, Wei-Liang Qian

Abstract: The detection of gravitational waves from extreme-mass-ratio inspirals (EMRIs) in space-based antennas like Taiji and Laser Interferometer Space Antenna promises deep insights into strong-field gravity and black hole physics. However, the complex, highly degenerate, and nonconvex likelihood landscapes characteristic of EMRI parameter spaces pose severe challenges for conventional Markov chain Mont… ▽ More The detection of gravitational waves from extreme-mass-ratio inspirals (EMRIs) in space-based antennas like Taiji and Laser Interferometer Space Antenna promises deep insights into strong-field gravity and black hole physics. However, the complex, highly degenerate, and nonconvex likelihood landscapes characteristic of EMRI parameter spaces pose severe challenges for conventional Markov chain Monte Carlo (MCMC) methods. Under realistic instrumental noise and broad priors, these methods demand impractical computational costs but are prone to becoming trapped in local maxima, leading to biased and unreliable parameter estimates. To address these challenges, we introduce flow-matching MCMC (FM-MCMC), a novel Bayesian framework that integrates continuous normalizing flows (CNFs) with parallel tempering MCMC (PTMCMC). By generating high-likelihood regions via CNFs and refining them through PTMCMC, FM-MCMC enables robust exploration of the nontrivial parameter spaces, achieves orders-of-magnitude improvement in computational efficiency, and, more importantly, ensures statistically unbiased inference. By enabling real-time, unbiased parameter inference, FM-MCMC could unlock the full scientific potential of EMRI observations, and would serve as a scalable pipeline for precision gravitational-wave astronomy. △ Less

Submitted 18 August, 2026; v1 submitted 1 August, 2025; originally announced August 2025.

Journal ref: Research 9, 1055 (2026)

Ray-tracing image simulations of transparent objects with complex shape and inhomogeneous refractive index

Authors: Armin Kalita, Bryan Oller, Thomas Paula, Alexander Bußmann, Sebastian Marte, Gabriel Blaj, Raymond G. Sierra, Sandra Mous, Kirk A. Larsen, Xinxin Cheng, Matt J. Hayes, Kelsey Banta, Stella Lisova, Peter Nguyen, Serge A. H. Guillet, Divya Thanasekaran, Silke Nelson, Mengning Liang, Stefan Adami, Nikolaus A. Adams, Claudiu A. Stan

Abstract: Optical images of transparent three-dimensional objects can be different from a replica of the object's cross section in the image plane due to refraction at the surface or in the body of the object. Simulations of the object's image are thus needed for the visualization and validation of physical models. We report ray-tracing image simulations that achieved high physical fidelity, reproducing opt… ▽ More Optical images of transparent three-dimensional objects can be different from a replica of the object's cross section in the image plane due to refraction at the surface or in the body of the object. Simulations of the object's image are thus needed for the visualization and validation of physical models. We report ray-tracing image simulations that achieved high physical fidelity, reproducing optical behaviors and image features not rendered in previous studies. We replicated brightfield microscopy images of drops with complex shapes and images of pressure and shock waves traveling inside them. For high physical fidelity, the simulations must replicate the spatial and angular distribution of illumination rays, and both the experiment and the simulation must be designed for accurate optical modeling. The simulations are highly sensitive to the properties of the drops and can be used to diagnose and refine fluid dynamics models. The simulated images can also be optimized to extract multiple 3D properties from experimental images. Compared to specialized single-shot 3D imaging methods, this approach has the advantage that it preserves the experimental simplicity, the high resolution, and the visual interpretability characteristic to basic optical imaging. The techniques introduced here are directly applicable to optical microscopy, so they can be used in other fields, such as microfluidics and biology, to expand the type and the accuracy of three-dimensional information that can be extracted from basic optical images. △ Less

Submitted 21 April, 2026; v1 submitted 30 July, 2025; originally announced July 2025.

Comments: 9 figures, see journal version for high resolution figures and supplementary materials

Journal ref: Phys. Rev. Fluids, 11, 044908 (2026)

Imaging valence electron rearrangement in a chemical reaction using hard X-ray scattering

Authors: Ian Gabalski, Alice Green, Philipp Lenzen, Felix Allum, Matthew Bain, Surjendu Bhattacharyya, Mathew A. Britton, Elio G. Champenois, Xinxin Cheng, James P. Cryan, Taran Driver, Ruaridh Forbes, Douglas Garratt, Aaron M. Ghrist, Martin Graßl, Matthias F. Kling, Kirk A. Larsen, Mengning Liang, Ming-Fu Lin, Yusong Liu, Michael P. Minitti, Silke Nelson, Joseph S. Robinson, Philip H. Bucksbaum, Thomas J. A. Wolf , et al. (2 additional authors not shown)

Abstract: We have observed the signatures of valence electron rearrangement in photoexcited ammonia using ultrafast hard X-ray scattering. Time-resolved X-ray scattering is a powerful tool for imaging structural dynamics in molecules because of the strong scattering from the core electrons localized near each nucleus. Such core-electron contributions generally dominate the differential scattering signal, ma… ▽ More We have observed the signatures of valence electron rearrangement in photoexcited ammonia using ultrafast hard X-ray scattering. Time-resolved X-ray scattering is a powerful tool for imaging structural dynamics in molecules because of the strong scattering from the core electrons localized near each nucleus. Such core-electron contributions generally dominate the differential scattering signal, masking any signatures of rearrangement in the chemically important valence electrons. Ammonia represents an exception to the typically high core-to-valence electron ratio. We measured 9.8 keV X-ray scattering from gas-phase deuterated ammonia following photoexcitation via a 200 nm pump pulse to the 3s Rydberg state. We observed changes in the recorded scattering patterns due to the initial photoexcitation and subsequent deuterium dissociation. Ab initio calculations confirm that the observed signal is sensitive to the rearrangement of the single photoexcited valence electron as well as the interplay between adiabatic and nonadiabatic dissociation channels. The use of ultrafast hard X-ray scattering to image the structural rearrangement of single valence electrons constitutes an important advance in tracking valence electronic structure in photoexcited atoms and molecules. △ Less

Submitted 23 June, 2025; originally announced June 2025.

Accelerating Stochastic Gravitational Wave Backgrounds Parameter Estimation in Pulsar Timing Arrays with Flow Matching

Authors: Bo Liang, Chang Liu, Tianyu Zhao, Minghui Du, Manjia Liang, Ruijun Shi, Hong Guo, Yuxiang Xu, Li-e Qiang, Peng Xu, Wei-Liang Qian, Ziren Luo

Abstract: Pulsar timing arrays (PTAs) are essential tools for detecting the stochastic gravitational wave background (SGWB), but their analysis faces significant computational challenges. Traditional methods like Markov-chain Monte Carlo (MCMC) struggle with high-dimensional parameter spaces where noise parameters often dominate, while existing deep learning approaches fail to model the Hellings-Downs (HD)… ▽ More Pulsar timing arrays (PTAs) are essential tools for detecting the stochastic gravitational wave background (SGWB), but their analysis faces significant computational challenges. Traditional methods like Markov-chain Monte Carlo (MCMC) struggle with high-dimensional parameter spaces where noise parameters often dominate, while existing deep learning approaches fail to model the Hellings-Downs (HD) correlation or are validated only on synthetic datasets. We propose a flow-matching-based continuous normalizing flow (CNF) for efficient and accurate PTA parameter estimation. By focusing on the 10 most contributive pulsars from the NANOGrav 15-year dataset, our method achieves posteriors consistent with MCMC, with a Jensen-Shannon divergence below \(10^{-2}\) nat, while reducing sampling time from 50 hours to 4 minutes. Powered by a versatile embedding network and a reweighting loss function, our approach prioritizes the SGWB parameters and scales effectively for future datasets. It enables precise reconstruction of SGWB and opens new avenues for exploring vast observational data and uncovering potential new physics, offering a transformative tool for advancing gravitational wave astronomy. △ Less

Submitted 26 December, 2024; originally announced December 2024.

Rapid Parameter Estimation for Extreme Mass Ratio Inspirals Using Machine Learning

Authors: Bo Liang, Hong Guo, Tianyu Zhao, He wang, Herik Evangelinelis, Yuxiang Xu, Chang liu, Manjia Liang, Xiaotong Wei, Yong Yuan, Peng Xu, Minghui Du, Wei-Liang Qian, Ziren Luo

Abstract: Extreme-mass-ratio inspiral (EMRI) signals pose significant challenges in gravitational wave (GW) astronomy owing to their low-frequency nature and highly complex waveforms, which occupy a high-dimensional parameter space with numerous variables. Given their extended inspiral timescales and low signal-to-noise ratios, EMRI signals warrant prolonged observation periods. Parameter estimation becomes… ▽ More Extreme-mass-ratio inspiral (EMRI) signals pose significant challenges in gravitational wave (GW) astronomy owing to their low-frequency nature and highly complex waveforms, which occupy a high-dimensional parameter space with numerous variables. Given their extended inspiral timescales and low signal-to-noise ratios, EMRI signals warrant prolonged observation periods. Parameter estimation becomes particularly challenging due to non-local parameter degeneracies, arising from multiple local maxima, as well as flat regions and ridges inherent in the likelihood function. These factors lead to exceptionally high time complexity for parameter analysis while employing traditional matched filtering and random sampling methods. To address these challenges, the present study applies machine learning to Bayesian posterior estimation of EMRI signals, leveraging the recently developed flow matching technique based on ODE neural networks. Our approach demonstrates computational efficiency several orders of magnitude faster than the traditional Markov Chain Monte Carlo (MCMC) methods, while preserving the unbiasedness of parameter estimation. We show that machine learning technology has the potential to efficiently handle the vast parameter space, involving up to seventeen parameters, associated with EMRI signals. Furthermore, to our knowledge, this is the first instance of applying machine learning, specifically the Continuous Normalizing Flows (CNFs), to EMRI signal analysis. Our findings highlight the promising potential of machine learning in EMRI waveform analysis, offering new perspectives for the advancement of space-based GW detection and GW astronomy. △ Less

Submitted 12 September, 2024; originally announced September 2024.

Hybrid electromagnetic toroidal vortices

Authors: Ren Wang, Beier Ying, Shuai Shi, Junsong Wang, Bing-Zhong Wang, Musheng Liang, Yijie Shen

Abstract: The ubiquitous occurrence of toroidal vortices or vortex rings in fluid-dynamic scenarios in nature has garnered significant attention of scientific frontier, whilst, the electromagnetic counterparts of which were only proposed recently with two distinct manifestations: vector toroidal pulses [Nat. Photon. 16, 523 (2022)] and scalar phase toroidal vortices [Nat. Photon. 16, 519 (2022)]. This dicho… ▽ More The ubiquitous occurrence of toroidal vortices or vortex rings in fluid-dynamic scenarios in nature has garnered significant attention of scientific frontier, whilst, the electromagnetic counterparts of which were only proposed recently with two distinct manifestations: vector toroidal pulses [Nat. Photon. 16, 523 (2022)] and scalar phase toroidal vortices [Nat. Photon. 16, 519 (2022)]. This dichotomy in the understanding of toroidal vortex phenomena has prompted a reassessment of their fundamental nature. Herein, we theoretically propose a novel form of electromagnetic toroidal vortex solutions, that uniquely integrate both scalar and vector characteristics, challenging the prevailing notion of their mutual exclusivity. We also present the experimental generation of the hybrid toroidal vortex pulses by a compact coaxial horn emitter augmented with a metasurface. This methodology not only demonstrates the feasibility of creating such complex vortex structures but also endows the resulting pulses with unique properties, including the coexistence of transverse orbital angular momentum, electromagnetic vortex streets, and topological skyrmion textures. These attributes introduce new dimensions in topologically complex structured waves, opening avenues for enhanced free-space information transmission, topologically nontrivial light-matter interaction and microscopy techniques. △ Less

Submitted 19 August, 2024; originally announced August 2024.

Towards a dynamically reconfigurable pixelated reflective display: Focused ion beam for phase-change metapixel structures

Authors: Daniel T. Yimam, Minpeng Liang, Jianting Ye, Bart J. Kooi

Abstract: The switching and optical properties of phase-change thin films are actively investigated for future smart optical devices. The possibility of having more than one stable state, the large optical contrast between phases, and the fast and reversible switching are some attractive properties driving the research interest. Optical devices based on phase change alloys are considered the frontier conten… ▽ More The switching and optical properties of phase-change thin films are actively investigated for future smart optical devices. The possibility of having more than one stable state, the large optical contrast between phases, and the fast and reversible switching are some attractive properties driving the research interest. Optical devices based on phase change alloys are considered the frontier contenders for tunable photonics. The combination of vivid structural color formation, with partial amorphization/crystallization of phase change alloys, and the associated optical tunability could be integrated into an energy-efficient reflective display device with high pixel density. This work demonstrates a contrast formation due to relative height differences from isolated pixelated structures. A reflective heterostructure device consisting of a low-loss Sb2Se3 alloy on a gold substrate was produced. With a focused ion beam, a pixelated metasurface structure was produced. Moreover, the ability to create local height differences using an ion beam was employed to create a structural color combination mimicking traditional LED like RGB pixels. We believe our approach in creating metapixels on phase change thin film surfaces could open up research interest in phase change alloys and moving away from semi/static plasmonic systems into truly dynamic display devices. △ Less

Submitted 13 February, 2024; originally announced February 2024.

FPM-INR: Fourier ptychographic microscopy image stack reconstruction using implicit neural representations

Authors: Haowen Zhou, Brandon Y. Feng, Haiyun Guo, Siyu Lin, Mingshu Liang, Christopher A. Metzler, Changhuei Yang

Abstract: Image stacks provide invaluable 3D information in various biological and pathological imaging applications. Fourier ptychographic microscopy (FPM) enables reconstructing high-resolution, wide field-of-view image stacks without z-stack scanning, thus significantly accelerating image acquisition. However, existing FPM methods take tens of minutes to reconstruct and gigabytes of memory to store a hig… ▽ More Image stacks provide invaluable 3D information in various biological and pathological imaging applications. Fourier ptychographic microscopy (FPM) enables reconstructing high-resolution, wide field-of-view image stacks without z-stack scanning, thus significantly accelerating image acquisition. However, existing FPM methods take tens of minutes to reconstruct and gigabytes of memory to store a high-resolution volumetric scene, impeding fast gigapixel-scale remote digital pathology. While deep learning approaches have been explored to address this challenge, existing methods poorly generalize to novel datasets and can produce unreliable hallucinations. This work presents FPM-INR, a compact and efficient framework that integrates physics-based optical models with implicit neural representations (INR) to represent and reconstruct FPM image stacks. FPM-INR is agnostic to system design or sample types and does not require external training data. In our demonstrated experiments, FPM-INR substantially outperforms traditional FPM algorithms with up to a 25-fold increase in speed and an 80-fold reduction in memory usage for continuous image stack representations. △ Less

Submitted 31 October, 2023; v1 submitted 27 October, 2023; originally announced October 2023.

Comments: Project Page: https://hwzhou2020.github.io/FPM-INR-Web/

Structural colors and enhanced resolution at the nanoscale: Local structuring of phase-change materials using focused ion beam

Authors: Daniel T. Yimam, Minpeng Liang, Jianting Ye, Bart J. Kooi

Abstract: In the past few years, phase-change materials have become increasingly important in nano-photonics and optoelectronics. The advantages of sizeable optical contrast between phases and the additional degree of freedom from phase switching have been the driving force. From multilevel reflectance to dynamic nanoprinting and structural colors, phase-change materials have achieved outstanding results wi… ▽ More In the past few years, phase-change materials have become increasingly important in nano-photonics and optoelectronics. The advantages of sizeable optical contrast between phases and the additional degree of freedom from phase switching have been the driving force. From multilevel reflectance to dynamic nanoprinting and structural colors, phase-change materials have achieved outstanding results with prospects for real-world applications. The local crystallization/amorphization of phase-change materials and the corresponding reflectance tunning by the crystallized/amorphized region size have potential applications for future dynamic display devices. Although the resolution is much higher than current display devices, the pixel sizes in those devices are limited by the locally switchable structure size. Here, we reduce the spot sizes further by using ion beams instead of laser beams and dramatically increase the pixel density, demonstrating the capability of having superior resolution. In addition, the power to sputter away materials can be utilized in creating nanostructures with relative height differences and local contrast. Our experiment focuses on one archetypal phase-change material, Sb$_2$Se$_3$, prepared by pulsed-laser deposition on a reflective gold substrate. We demonstrate that we can produce structural colors and achieve reflectance tunning by focused ion beam milling/sputtering of phase change materials at the nanoscale. Furthermore, we show that the local structuring of phase-change materials by focused ion beam can be used to produce high pixel density display devices with superior resolutions. △ Less

Submitted 29 January, 2023; originally announced January 2023.

Comments: nanophotonics, focused ion beam, nanoprinting, pulsed laser deposition, phase change materials

Search for relativistic fractionally charged particles in space

Authors: DAMPE Collaboration, F. Alemanno, C. Altomare, Q. An, P. Azzarello, F. C. T. Barbato, P. Bernardini, X. J. Bi, M. S. Cai, E. Casilli, E. Catanzani, J. Chang, D. Y. Chen, J. L. Chen, Z. F. Chen, M. Y. Cui, T. S. Cui, Y. X. Cui, H. T. Dai, A. De-Benedittis, I. De Mitri, F. de Palma, M. Deliyergiyev, A. Di Giovanni, M. Di Santo , et al. (126 additional authors not shown)

Abstract: More than a century after the performance of the oil drop experiment, the possible existence of fractionally charged particles FCP still remains unsettled. The search for FCPs is crucial for some extensions of the Standard Model in particle physics. Most of the previously conducted searches for FCPs in cosmic rays were based on experiments underground or at high altitudes. However, there have been… ▽ More More than a century after the performance of the oil drop experiment, the possible existence of fractionally charged particles FCP still remains unsettled. The search for FCPs is crucial for some extensions of the Standard Model in particle physics. Most of the previously conducted searches for FCPs in cosmic rays were based on experiments underground or at high altitudes. However, there have been few searches for FCPs in cosmic rays carried out in orbit other than AMS-01 flown by a space shuttle and BESS by a balloon at the top of the atmosphere. In this study, we conduct an FCP search in space based on on-orbit data obtained using the DArk Matter Particle Explorer (DAMPE) satellite over a period of five years. Unlike underground experiments, which require an FCP energy of the order of hundreds of GeV, our FCP search starts at only a few GeV. An upper limit of $6.2\times 10^{-10}~~\mathrm{cm^{-2}sr^{-1} s^{-1}}$ is obtained for the flux. Our results demonstrate that DAMPE exhibits higher sensitivity than experiments of similar types by three orders of magnitude that more stringently restricts the conditions for the existence of FCP in primary cosmic rays. △ Less

Submitted 9 September, 2022; originally announced September 2022.

Comments: 19 pages, 6 figures, accepted by PRD

Report number: 106, 063026

Journal ref: Physical Review D 106.6 (2022): 063026

Computational Approaches to Model X-ray Photon Correlation Spectroscopy from Molecular Dynamics

Authors: Shaswat Mohanty, Christopher B. Cooper, Hui Wang, Mengning Liang, Wei Cai

Abstract: X-ray photon correlation spectroscopy (XPCS) allows for the resolution of dynamic processes within a material across a wide range of length and time scales. X-ray speckle visibility spectroscopy (XSVS) is a related method that uses a single diffraction pattern to probe ultrafast dynamics. Interpretation of the XPCS and XSVS data in terms of underlying physical processes is necessary to establish t… ▽ More X-ray photon correlation spectroscopy (XPCS) allows for the resolution of dynamic processes within a material across a wide range of length and time scales. X-ray speckle visibility spectroscopy (XSVS) is a related method that uses a single diffraction pattern to probe ultrafast dynamics. Interpretation of the XPCS and XSVS data in terms of underlying physical processes is necessary to establish the connection between the macroscopic responses and the microstructural dynamics. To aid the interpretation of the XPCS and XSVS data, we present a computational framework to model these experiments by computing the X-ray scattering intensity directly from the atomic positions obtained from molecular dynamics (MD) simulations. We compare the efficiency and accuracy of two alternative computational methods: the direct method computing the intensity at each diffraction vector separately, and a method based on fast Fourier transform that computes the intensities at all diffraction vectors at once. The computed X-ray speckle patterns capture the density fluctuations over a range of length and time scales and are shown to reproduce the known properties and relations of experimental XPCS and XSVS for liquids. △ Less

Submitted 5 January, 2023; v1 submitted 27 April, 2022; originally announced April 2022.

Comments: 31 pages, 11 figures, submitted to Modelling and Simulations in Materials Science and Engineering

Journal ref: Modelling and Simulation in Materials Science and Engineering 30 (2022) 075004

Probabilistic Bearing Fault Diagnosis Using Gaussian Process with Tailored Feature Extraction

Authors: Mingxuan Liang, Kai Zhou

Abstract: Rolling bearings are subject to various faults due to its long-time operation under harsh environment, which will lead to unexpected breakdown of machinery system and cause severe accidents. Deep learning methods recently have gained growing interests and extensively applied in the data-driven bearing fault diagnosis. However, current deep learning methods perform the bearing fault diagnosis in th… ▽ More Rolling bearings are subject to various faults due to its long-time operation under harsh environment, which will lead to unexpected breakdown of machinery system and cause severe accidents. Deep learning methods recently have gained growing interests and extensively applied in the data-driven bearing fault diagnosis. However, current deep learning methods perform the bearing fault diagnosis in the form of deterministic classification, which overlook the uncertainties that inevitably exist in actual practice. To tackle this issue, in this research we develop a probabilistic fault diagnosis framework that can account for the uncertainty effect in prediction, which bears practical significance. This framework fully leverages the probabilistic feature of Gaussian process classifier (GPC). To facilitate the establishment of high-fidelity GPC, the tailored feature extraction with dimensionality reduction method can be optimally determined through the cross validation-based grid search upon a prespecified method pool consisting of various kernel principal component analysis (KPCA) methods and stacked autoencoder. This strategy can ensure the complex nonlinear relations between the features and faults to be adequately characterized. Furthermore, the sensor fusion concept is adopted to enhance the diagnosis performance. As compared with the traditional deep learning methods, this proposed framework usually requires less labeled data and less effort for parameter tuning. Systematic case studies using the publicly accessible experimental rolling bearing dataset are carried out to validate this new framework. Various influencing factors on fault diagnosis performance also are thoroughly investigated. △ Less

Submitted 19 September, 2021; originally announced September 2021.

Realization of Qi-Wu-Zhang model in spin-orbit-coupled ultracold fermions

Authors: Ming-Cheng Liang, Yu-Dong Wei, Long Zhang, Xu-Jie Wang, Han Zhang, Wen-Wei Wang, Wei Qi, Xiong-Jun Liu, Xibo Zhang

Abstract: Based on the optical Raman lattice technique, we experimentally realize the Qi-Wu-Zhang model for quantum anomalous Hall phase in ultracold fermions with two-dimensional (2D) spin-orbit (SO) coupling. We develop a novel protocol of pump-probe quench measurement to probe, with minimal heating, the resonant spin flipping on particular quasi-momentum subspace called band-inversion surfaces. With this… ▽ More Based on the optical Raman lattice technique, we experimentally realize the Qi-Wu-Zhang model for quantum anomalous Hall phase in ultracold fermions with two-dimensional (2D) spin-orbit (SO) coupling. We develop a novel protocol of pump-probe quench measurement to probe, with minimal heating, the resonant spin flipping on particular quasi-momentum subspace called band-inversion surfaces. With this protocol we demonstrate the first Dirac-type 2D SO coupling in a fermionic system, and detect non-trivial band topology by observing the change of band-inversion surfaces as the two-photon detuning varies. The non-trivial band topology is also observed by slowly loading the atoms into optical Raman lattices and measuring the spin textures. Our results show solid evidence for the realization of the minimal SO-coupled quantum anomalous Hall model, which can provide a feasible platform to investigate novel topological physics including the correlation effects with SO-coupled ultracold fermions. △ Less

Submitted 20 July, 2022; v1 submitted 18 September, 2021; originally announced September 2021.

Comments: 7 pages, 4 figures in the main text, and 6 pages, 3 figures in the supplemental material

Journal ref: Physical Review Research 5, L012006 (2023)

Non-iterative complex wave-field reconstruction based on Kramers-Kronig relations

Authors: Cheng Shen, An Pan, Mingshu Liang, Changhuei Yang

Abstract: A new computational imaging method to reconstruct the complex wave-field is reported. Due to the existence of zero frequency component, the measured signal by amplitude modulation of pupil has a spectrum similar to the one of off-axis hologram. The mathematical analogy between them is established in this paper. Based on this observation and analyticity of band-limited signal under any diffraction-… ▽ More A new computational imaging method to reconstruct the complex wave-field is reported. Due to the existence of zero frequency component, the measured signal by amplitude modulation of pupil has a spectrum similar to the one of off-axis hologram. The mathematical analogy between them is established in this paper. Based on this observation and analyticity of band-limited signal under any diffraction-limited system, an algorithm from Kramers-Kronig (KK) relations is utilized to recover the phase information only from the intensity patterns. From the sensing side, only two measurements are required at least. From the reconstruction algorithm side, our method is iteration-free and parameter-free, also without any assumption on sample characteristics. It owns several advantages over existing phase imaging methods and could provide a unique perspective to understand current computational imaging methods. △ Less

Submitted 11 May, 2020; originally announced May 2020.

X-ray diffractive imaging of controlled gas-phase molecules: Toward imaging of dynamics in the molecular frame

Authors: Thomas Kierspel, Andrew Morgan, Joss Wiese, Terry Mullins, Andy Aquila, Anton Barty, Richard Bean, Rebecca Boll, Sébastien Boutet, Philip Bucksbaum, Henry N. Chapman, Lauge Christensen, Alan Fry, Mark Hunter, Jason E. Koglin, Mengning Liang, Valerio Mariani, Adi Natan, Joseph Robinson, Daniel Rolles, Artem Rudenko, Kirsten Schnorr, Henrik Stapelfeldt, Stephan Stern, Jan Thøgersen , et al. (3 additional authors not shown)

Abstract: We report experimental results on the diffractive imaging of three-dimensionally aligned 2,5-diiodothiophene molecules. The molecules were aligned by chirped near-infrared laser pulses, and their structure was probed at a photon energy of 9.5 keV ($λ\approx130 \text{pm}$) provided by the Linac Coherent Light Source. Diffracted photons were recorded on the CSPAD detector and a two-dimensional diffr… ▽ More We report experimental results on the diffractive imaging of three-dimensionally aligned 2,5-diiodothiophene molecules. The molecules were aligned by chirped near-infrared laser pulses, and their structure was probed at a photon energy of 9.5 keV ($λ\approx130 \text{pm}$) provided by the Linac Coherent Light Source. Diffracted photons were recorded on the CSPAD detector and a two-dimensional diffraction pattern of the equilibrium structure of 2,5-diiodothiophene was recorded. The retrieved distance between the two iodine atoms agrees with the quantum-chemically calculated molecular structure to within 5 %. The experimental approach allows for the imaging of intrinsic molecular dynamics in the molecular frame, albeit this requires more experimental data which should be readily available at upcoming high-repetition-rate facilities. △ Less

Submitted 7 February, 2020; v1 submitted 29 October, 2019; originally announced October 2019.

The DArk Matter Particle Explorer mission

Authors: J. Chang, G. Ambrosi, Q. An, R. Asfandiyarov, P. Azzarello, P. Bernardini, B. Bertucci, M. S. Cai, M. Caragiulo, D. Y. Chen, H. F. Chen, J. L. Chen, W. Chen, M. Y. Cui, T. S. Cui, A. D'Amone, A. De Benedittis, I. De Mitri, M. Di Santo, J. N. Dong, T. K. Dong, Y. F. Dong, Z. X. Dong, G. Donvito, D. Droz , et al. (139 additional authors not shown)

Abstract: The DArk Matter Particle Explorer (DAMPE), one of the four scientific space science missions within the framework of the Strategic Pioneer Program on Space Science of the Chinese Academy of Sciences, is a general purpose high energy cosmic-ray and gamma-ray observatory, which was successfully launched on December 17th, 2015 from the Jiuquan Satellite Launch Center. The DAMPE scientific objectives… ▽ More The DArk Matter Particle Explorer (DAMPE), one of the four scientific space science missions within the framework of the Strategic Pioneer Program on Space Science of the Chinese Academy of Sciences, is a general purpose high energy cosmic-ray and gamma-ray observatory, which was successfully launched on December 17th, 2015 from the Jiuquan Satellite Launch Center. The DAMPE scientific objectives include the study of galactic cosmic rays up to $\sim 10$ TeV and hundreds of TeV for electrons/gammas and nuclei respectively, and the search for dark matter signatures in their spectra. In this paper we illustrate the layout of the DAMPE instrument, and discuss the results of beam tests and calibrations performed on ground. Finally we present the expected performance in space and give an overview of the mission key scientific goals. △ Less

Submitted 14 September, 2017; v1 submitted 26 June, 2017; originally announced June 2017.

Comments: 45 pages, including 29 figures and 6 tables. Published in Astropart. Phys

Journal ref: Astropart. Phys. 95 (2017) 6-24

Strongly aligned gas-phase molecules at Free-Electron Lasers

Authors: Thomas Kierspel, Joss Wiese, Terry Mullins, Joseph Robinson, Andy Aquila, Anton Barty, Richard Bean, Rebecca Boll, Sébastien Boutet, Philip Bucksbaum, Henry N. Chapman, Lauge Christensen, Alan Fry, Mark Hunter, Jason E. Koglin, Mengning Liang, Valerio Mariani, Andrew Morgan, Adi Natan, Vladimir Petrovic, Daniel Rolles, Artem Rudenko, Kirsten Schnorr, Henrik Stapelfeldt, Stephan Stern , et al. (5 additional authors not shown)

Abstract: We demonstrate a novel experimental implementation to strongly align molecules at full repetition rates of free-electron lasers. We utilized the available in-house laser system at the coherent x-ray imaging beamline at the Linac Coherent Light Source. Chirped laser pulses, i. e., the direct output from the regenerative amplifier of the Ti:Sa chirped pulse amplification laser system, were used to s… ▽ More We demonstrate a novel experimental implementation to strongly align molecules at full repetition rates of free-electron lasers. We utilized the available in-house laser system at the coherent x-ray imaging beamline at the Linac Coherent Light Source. Chirped laser pulses, i. e., the direct output from the regenerative amplifier of the Ti:Sa chirped pulse amplification laser system, were used to strongly align 2,5-diiodothiophene molecules in a molecular beam. The alignment laser pulses had pulse energies of a few mJ and a pulse duration of 94 ps. A degree of alignment of $\left<\cos^2\!θ_{2D}\right>$ = 0.85 was measured, limited by the intrinsic temperature of the molecular beam rather than by the available laser system. With the general availability of synchronized chirped-pulse-amplified near-infrared laser systems at short-wavelength laser facilities, our approach allows for the universal preparation of molecules tightly fixed in space for experiments with x-ray pulses. △ Less

Submitted 17 October, 2015; v1 submitted 11 June, 2015; originally announced June 2015.

Comments: 10 pages, 5 figures

Journal ref: J. Phys. B: At. Mol. Opt. Phys. 48 (2015) 204002

Experimental study of a terahertz time-domain spectrometer based on photoconductive antenna

Authors: Jitao Zhang, Wei-Ren Ng, Mingguang Tuo, Min Liang, M. E. Gehm, Hao Xin

Abstract: We construct a terahertz time-domain spectrometer (THz-TDS) system based on photoconductive antenna (PCA). A 800 nm Ti sapphire femtosecond laser with 80 MHz repetition rate provides the pump and probe laser pulse, which has a 45 fs pulse width (as short as 15 fs is available) and as much as 400 mW power. Two commercial PCAs with 34 um and 6 um gap size are used as the emitter and receiver, respec… ▽ More We construct a terahertz time-domain spectrometer (THz-TDS) system based on photoconductive antenna (PCA). A 800 nm Ti sapphire femtosecond laser with 80 MHz repetition rate provides the pump and probe laser pulse, which has a 45 fs pulse width (as short as 15 fs is available) and as much as 400 mW power. Two commercial PCAs with 34 um and 6 um gap size are used as the emitter and receiver, respectively. We characterize this system by measuring its absolute radiated THz power, spectral bandwidth, signal-to-noise ratio (SNR), dynamic range and beam profile at the focal plane. We further analyze the noise sources of the THz-TDS system and specifically discuss the possibility to improve the DR and SNR. In addition, using this system, we study the response of the PCA to various parameters, such as laser power, biased voltage, beam spot's location and laser's polarization. △ Less

Submitted 7 August, 2014; v1 submitted 9 February, 2014; originally announced February 2014.

Comments: 13 pages,8 figures. This paper has been withdrawn by the author due to an supplement of a new result

Cryptotomography: reconstructing 3D Fourier intensities from randomly oriented single-shot diffraction patterns

Authors: N. D. Loh, M. Bogan, V. Elser, A. Barty, S. Boutet, S. Bajt, J. Hajdu, T. Ekeberg, F. R. N. C. Maia, J. Schulz, M. M. Seibert, B. Iwan, N. Timneanu, S. Marchesini, I. Schlichting, R. L. Shoeman, L. Lomb, M. Frank, M. Liang, H. N. Chapman

Abstract: We reconstructed the 3D Fourier intensity distribution of mono-disperse prolate nano-particles using single-shot 2D coherent diffraction patterns collected at DESY's FLASH facility when a bright, coherent, ultrafast X-ray pulse intercepted individual particles of random, unmeasured orientations. This first experimental demonstration of cryptotomography extended the Expansion-Maximization-Compres… ▽ More We reconstructed the 3D Fourier intensity distribution of mono-disperse prolate nano-particles using single-shot 2D coherent diffraction patterns collected at DESY's FLASH facility when a bright, coherent, ultrafast X-ray pulse intercepted individual particles of random, unmeasured orientations. This first experimental demonstration of cryptotomography extended the Expansion-Maximization-Compression (EMC) framework to accommodate unmeasured fluctuations in photon fluence and loss of data due to saturation or background scatter. This work is an important step towards realizing single-shot diffraction imaging of single biomolecules. △ Less

Submitted 5 April, 2010; v1 submitted 3 March, 2010; originally announced March 2010.

Comments: 4 pages, 4 figures