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Physics-informed genetic algorithms (PIGAs) facilitating LIBS spectral normalization with shockwave characteristics
Authors:
Ying Zhou,
Jian Wu,
Mingxin Shi,
Minxin Chen,
Jinghui Li,
Xinyu Guo,
Yuhua Hang,
Cuixiang Pei,
Xingwen Li
Abstract:
Inspired by physics-informed neural networks (PINNs) inheriting both the interpretability of physical laws and the efficient integration capability of machine learning, we propose a framework based on stoichiometric ablation for LIBS spectral normalization, encoding physical constraints between LIBS intensities and shockwave characteristics (temperature Tshock and pressure P) into optimization alg…
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Inspired by physics-informed neural networks (PINNs) inheriting both the interpretability of physical laws and the efficient integration capability of machine learning, we propose a framework based on stoichiometric ablation for LIBS spectral normalization, encoding physical constraints between LIBS intensities and shockwave characteristics (temperature Tshock and pressure P) into optimization algorithms with multiple independent objectives, named physics-informed genetic algorithms (PIGAs). It is characterized by its applicability to the wider laser energy range covering laser-induced breakdown to significant plasma shielding and spectral lines undergoing self-absorption outperforming the widely-used physical linear or multivariate data-driven normalization methods. The home-made end-to-end LAP-RTE codes serves as the benchmark to validate the physical reciprocal-logarithmic transformation and its extensibility to self-absorption spectral lines for PIGAs. Next experimental spectral lines are statistically used to validate PIGAs correction effects, the median RSDs of spectral intensities can be effectively reduced by 85% (corrected by P) and 88% (corrected by Tshock) for 108 Fe I lines, while for 33 Fe II lines, reduced by 77% (corrected by P) and 86% (corrected by Tshock). Seventeen self-absorption lines are also corrected effectively, with RSDs being reduced by 78% (corrected by P) and 89% (corrected by Tshock). Our proposed idea of combining optimization methods to quantify unknown parameters in normalization strategies can also be extended to excavate the correlation between parameters for other low-temperature plasma fields with similar processes.
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Submitted 24 July, 2026;
originally announced August 2026.
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Measurement of multiple mechanical properties from multi-dimensional signals in nanosecond laser ablation via PINN
Authors:
Ying Zhou,
Jian Wu,
Ziyuan Song,
Jinghui Li,
Xinyu Guo,
Hao Sun,
Yuhua Hang,
Cuixiang Pei,
Xingwen Li
Abstract:
Accurate evaluation of mechanical properties in steels under ageing or service conditions remains a major challenge. We propose a thermo-mechanical coupling framework for nanosecond laser ablation based on energy conservation, which is embedded into a physics-informed neural network (PINN) to enable simultaneous inversion of multiple mechanical properties. A thermo-mechanical coupling coefficient…
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Accurate evaluation of mechanical properties in steels under ageing or service conditions remains a major challenge. We propose a thermo-mechanical coupling framework for nanosecond laser ablation based on energy conservation, which is embedded into a physics-informed neural network (PINN) to enable simultaneous inversion of multiple mechanical properties. A thermo-mechanical coupling coefficient is defined to uniformly describe the dynamic allocation of input laser energy among thermal diffusion, mechanical work and plasma shielding across different deformation stages under laser irradiation. Furthermore, hard-to-measure physical characteristics in the coupled equation are replaced with experimentally accessible features obtained through the simultaneous acquisition of spectroscopic, shockwave and surface-wave signals. Using 210 experimental datasets, the framework simultaneously recovers Young's modulus, yield strength, ultimate tensile strength and micro-Vickers hardness with high accuracy (R2=0.9927, 0.9912, 0.9916 and 0.9959 respectively), significantly outperforming the baseline method (ultrasonic velocity regression for E, R2=0.0012). Comparisons with linear normalization and unconstrained neural networks demonstrate that PINN achieves near-unity accuracy through the embedding of conservation-law constraints. Partial dependency analysis further uncovers the nonlinear coupling laws between input features and mechanical properties. The proposed paradigm, integrating conservation laws, measurable features and physics-informed learning, offers a universal approach for non-contact, high-precision and physically consistent multi-to-multi inversion of multiple material properties under nanosecond laser ablation conditions.
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Submitted 29 July, 2026;
originally announced July 2026.
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Coupling model of metallic target ablation-plasma evolution-radiation under nanosecond laser irradiation
Authors:
Ying Zhou,
Jian Wu,
Hao Sun,
Jinghui Li,
Xiaoxuan Li,
Shuzhi Huang,
Jiayao He,
Xingyu Liu,
Yuhua Hang,
Cuixiang Pei,
Xingwen Li
Abstract:
The interaction of nanosecond laser pulses with metallic materials involves multiple complex physical processes. It is challenging to construct a self-consistent model capable of uniformly describing all stages. This work establishes a multi-physics coupling model for pure iron, encompassing laser energy deposition, solid-liquid phase transition, gas-liquid interfacial kinetic transport, plasma ex…
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The interaction of nanosecond laser pulses with metallic materials involves multiple complex physical processes. It is challenging to construct a self-consistent model capable of uniformly describing all stages. This work establishes a multi-physics coupling model for pure iron, encompassing laser energy deposition, solid-liquid phase transition, gas-liquid interfacial kinetic transport, plasma expansion and ionization, and spectral radiation. The numerical solution adopts a partition method, utilizing an implicit compact difference scheme for the target and a Mac-Cormack explicit scheme for the plasma. The simulations elucidate the emergence of plasma shielding and its inhibitory effect on the evaporation process, thereby confirming that 81.6% of the early-stage ablation products are transported through a supersonic expansion mode. The model successfully captures the complete evolution of the plasma plume from a high-temperature, highly ionized state to a low-temperature, neutral atomic state. Based on this, spectral calculations demonstrate the dynamic evolution of radiative characteristics from an early stage featuring a strong continuum background dominated by ion lines to a later stage where the continuum attenuates, atomic lines become prominent, and self-absorption appears. The emergence of self-absorption proves the ability of the model to effectively capture the optical thickness effects arising from spatial inhomogeneity within the plasma. Through systematic comparison between experimentally measured spectra and calculated results from the PrismSPECT and NIST LIBS spectral programs, the model presented here achieves the highest comprehensive scores in quantitative evaluations of multiple channels. This validates the necessity and superiority of the full-chain self-consistent modeling approach, especially in describing plasma inhomogeneity and radiation transport.
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Submitted 24 July, 2026;
originally announced July 2026.
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A nuclear clock based on $^{229}$Th
Authors:
Beichen Huang,
Gaowei Yan,
Qi Xiao,
Wenhao Bu,
Zhen Zhang,
Chengchun Zhao,
Chao Yan,
Zhi-Ang Chen,
Peixiong Zhang,
Gleb Penyazkov,
Zhenhai Zhan,
Lingfeng Yan,
Yuefei Wang,
Lin Li,
Shanming Li,
Xiaobo Qian,
Xuegang Liu,
Qiange He,
Taoxiang Sun,
Haochen Tian,
Binkun Lu,
Ningyuan Ma,
Juxian Li,
Yanzhang Wu,
Qiaorui Gong
, et al. (13 additional authors not shown)
Abstract:
Atomic clocks have made time and frequency the most precisely measured quantities in physics, progressing from microwave standards that realize the SI second to optical clocks that now reach unprecedented levels of precision. A nuclear clock would shift the frequency reference from an electronic transition to the uniquely low-lying, laser-accessible isomeric transition in the $^{229}$Th nucleus, o…
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Atomic clocks have made time and frequency the most precisely measured quantities in physics, progressing from microwave standards that realize the SI second to optical clocks that now reach unprecedented levels of precision. A nuclear clock would shift the frequency reference from an electronic transition to the uniquely low-lying, laser-accessible isomeric transition in the $^{229}$Th nucleus, offering a route to compact, robust timekeeping and sensitive tests of fundamental physics. However, turning recent advances in spectroscopy of the $^{229}$Th nuclear resonance into clock operation requires the nuclear transition to serve as a stable discriminator for steering a traceable oscillator. Here we demonstrate the operation of a $^{229}$Th nuclear clock by stabilizing a continuous-wave narrow-linewidth 148.4 nm vacuum-ultraviolet (VUV) laser to a resolved nuclear transition in a solid-state host. This clock operation is enabled by fast frequency discrimination based on phototube photocurrent readout of the transmitted VUV power. The 10 $μ$W VUV laser, generated by four-wave mixing in cadmium vapour, provides a high-signal-to-noise absorption signal from a home-grown $^{229}$Th:CaF$_2$ crystal, allowing the laser to be locked to a weakly temperature-sensitive nuclear transition. The clock reaches a fractional frequency instability of $2\times10^{-12}/\sqrt{τ/s} $, where $τ$ is the averaging time. Remarkably, nuclear-clock frequencies measured with two distinct crystals agree at the $10^{-13}$ level, demonstrating the reproducibility of solid-state nuclear frequency references. By making a laser-addressed atomic nucleus an operational clock reference, this work extends quantum metrology from electronic to nuclear transitions, and opens a new platform for compact clocks, solid-state nuclear quantum sensors and precision tests of fundamental physics.
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Submitted 7 June, 2026;
originally announced June 2026.
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Thorium doped strontium fluoride crystal: a unique candidate for solid nuclear optical clock material
Authors:
Qiaorui Gong,
Shanming Li,
Shulong Zhang,
Siliang Tao,
Guoliang Deng,
Peixiong Zhang,
Chengchun Zhao,
Yin Hang,
Shining Zhu,
Longsheng Ma
Abstract:
We report a candidate with unique advantages in the cultivation of solid-state nuclear clock material, Th:SrF2 crystal. It not only has a segregation coefficient close to 1, which can achieve highly efficient and uniform doping of Th, but also ensures a high transmittance (~69% at 150 nm) while achieving extremely high doping concentration (232Th>6*10^20 cm^(-3). In addition, SrF2 crystal will not…
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We report a candidate with unique advantages in the cultivation of solid-state nuclear clock material, Th:SrF2 crystal. It not only has a segregation coefficient close to 1, which can achieve highly efficient and uniform doping of Th, but also ensures a high transmittance (~69% at 150 nm) while achieving extremely high doping concentration (232Th>6*10^20 cm^(-3). In addition, SrF2 crystal will not be irradiated-colored under strong α radiation like CaF2 crystal, Th:SrF2 crystal is expected to fully unleash its high concentration doping characteristics while ensuring its transmission performance in nuclear transition band not be severely affected by 229Th radiation damage.
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Submitted 3 July, 2024;
originally announced July 2024.
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Unraveling Ultrafast Photoionization in Hexagonal Boron Nitride
Authors:
Lianjie Xue,
Song Liu,
Yang Hang,
Adam M. Summers,
Derrek J. Wilson,
Xinya Wang,
Pingping Chen,
Thomas G. Folland,
Jordan A. Hachtel,
Hongyu Shi,
Sajed Hosseini-Zavareh,
Suprem R. Das,
Shuting Lei,
Zhuhua Zhang,
Christopher M. Sorensen,
Wanlin Guo,
Joshua D. Caldwell,
James H. Edgar,
Cosmin I. Blaga,
Carlos A. Trallero-Herrero
Abstract:
The non-linear response of dielectrics to intense, ultrashort electric fields has been a sustained topic of interest for decades with one of its most important applications being femtosecond laser micro/nano-machining. More recently, renewed interests in strong field physics of solids were raised with the advent of mid-infrared femtosecond laser pulses, such as high-order harmonic generation, opti…
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The non-linear response of dielectrics to intense, ultrashort electric fields has been a sustained topic of interest for decades with one of its most important applications being femtosecond laser micro/nano-machining. More recently, renewed interests in strong field physics of solids were raised with the advent of mid-infrared femtosecond laser pulses, such as high-order harmonic generation, optical-field-induced currents, etc. All these processes are underpinned by photoionization (PI), namely the electron transfer from the valence to the conduction bands, on a time scale too short for phononic motion to be of relevance. Here, in hexagonal boron nitride, we reveal that the bandgap can be finely manipulated by femtosecond laser pulses as a function of field polarization direction with respect to the lattice, in addition to the field's intensity. It is the modification of bandgap that enables the ultrafast PI processes to take place in dielectrics. We further demonstrate the validity of the Keldysh theory in describing PI in dielectrics in the few TW/cm2 regime.
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Submitted 26 January, 2021; v1 submitted 25 January, 2021;
originally announced January 2021.
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A Se vacancy induced localized Raman mode in two-dimensional MoSe2 grown by CVD
Authors:
Shudong Zhao,
Meilin Lu,
ShaSha Xue,
Lin Yan,
Peng Miao,
Yan Hang,
Xianjie Wang,
Zhiguo Liu,
Yi Wang,
Lei Tao,
Yu Sui,
Yang Wang
Abstract:
Defects play a significant role in optical properties of semiconducting two-dimensional transition metal dichalcogenides (TMDCs). In ultra-thin MoSe2, a remarkable feature at ~250 cm-1 in Raman spectra is ascribed to be a defect-related mode. Recent attempts failed to explain the origin of this peak, leaving it being a mystery. Here in this work, we demonstrate that this peak is a Se vacancy induc…
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Defects play a significant role in optical properties of semiconducting two-dimensional transition metal dichalcogenides (TMDCs). In ultra-thin MoSe2, a remarkable feature at ~250 cm-1 in Raman spectra is ascribed to be a defect-related mode. Recent attempts failed to explain the origin of this peak, leaving it being a mystery. Here in this work, we demonstrate that this peak is a Se vacancy induced defect mode. Heat effect and hydrogen etching are two main factors to introduce Se vacancies in CVD process of growing MoSe2. A phonon confinement model can well explain the behaviors of intrinsic Raman modes. Density functional theory (DFT) calculation reveals that single Se vacancy (VSe) is responsible for the appearance of Raman peak at ~250 cm-1 and this mode is an A1g-like localized mode which is also confirmed by polarized Raman scattering experiment. The relative strength of this mode can be a characterization of the quality of 2D MoSe2. This work may offer a simple method to tailor chalcogenide vacancies in 2D TMDCs and provide a way to study their vibrational properties.
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Submitted 22 April, 2019;
originally announced April 2019.