arXiv subjects

Liangliang Ji

Publications and source records attributed to Liangliang Ji.

At least 19 recordsLinked to original sources

arXiv2026

Macroscopic Coherent Axion Production by Reverse Parametric Fluorescence

We propose a macroscopically coherent laboratory source of axion-like particles (ALPs) through the axion--electron coupling $g_{ae}$. Two counterpropagating optical modes drive reverse parametric fluorescence in a crystal, where two pump photons are converted into a relativistic ALP through virtual ionic transitions, while the medium returns to its initial state. Phase matching enables emission amplitudes from many ions to add coherently without preparing material coherence. The pump frequencies determine the ALP energy, making the source continuously tunable. The production rate scales with the product of the two pump powers and the square of the source length. Resonant absorption followed by fluorescence completes the detection scheme. For benchmark crystal and laser parameters, a one-year operation gives a reach of $g_{ae}\simeq2.8\times10^{-11}$, substantially improving the sensitivity of purely laboratory-based searches for low-mass ALPs.

hep-ph↗

arXiv2026

Wakefield-Dressed Relativistic Vortex Electrons in Plasma Accelerators

Plasma wakefield acceleration is usually regarded as a classical mechanism for producing high- energy charged-particle beams. Here we show that an axisymmetric plasma wakefield can also act as a moving quantum structure that supports relativistic vortex electron states. Starting from the Dirac equation, we derive the electron spinor eigenstates with definite total angular momentum in an ideal bubble-regime wakefield. The transverse focusing field confines and quantizes the electron transverse motion into Laguerre-Gaussian vortex modes, while the longitudinal electric field acceler- ates the electron without destroying the symmetry-protected angular momenta. We further analyze the localized and off-axis vortex electron wave-packets, and non-ideal wakefield perturbations, and identify the conditions for preserving electron-vortex-state purity. These results suggest plasma wakefield as a route toward high-energy vortex electrons and extend plasma-based acceleration from classical beam dynamics to quantum-state control of relativistic particles.

physics.acc-ph↗

arXiv2026

Axion generation and detection in laser-plasma wakefields

The axions are compelling candidates for cold dark matter, but their extremely weak interaction with photons makes laboratory searches challenging. We show that the quasi-static electromagnetic fields of a laser-plasma wakefield, which can exceed $10^{11}$\,V/m, enable axion generation without an external production magnet and enhance the conversion rate by two orders of magnitude over a conventional magnetic production region. Self-consistent particle-in-cell simulations reveal two complementary routes to detection. In the first route, axions are reconverted into photons within the wakefield and laser fields, eliminating the need for a separate regeneration magnet but requiring to suppress the intense laser-plasma background. The regenerated photons have polarization, harmonic-frequency, and Laguerre-Gaussian transverse-mode signatures that are largely absent from the driving fields, allowing successive filters to isolate the signal. In the second route, axions traverse a wall and undergo reconversion in a downstream magnet, providing a much lower background at the cost of requiring both the magnet and a seed pulse for coherent amplification. For axion masses below $0.1$\,meV, meter-scale wakefield guiding under our stated assumptions yields a projected coupling sensitivity down to $3.9\times10^{-12}\,\mathrm{GeV}^{-1}$, surpassing the projected constraint of next-generation laboratory searches. These results establish ultra-strong plasma wakefields as a magnet-free axion source with two experimentally distinct and complementary detection strategies.

physics.plasm-ph↗

arXiv2026

A plasma photocathode for spin-polarized electron beams via state-selected hydrogen halide photofragments

Spin-polarized electron beams are essential tools for probing fundamental symmetries and for the search beyond the Standard Model. While plasma-based accelerators are a promising pathway towards higher-energy frontiers, they have so far failed to deliver a competitive polarized source: existing proposals are challenging to realize and achievable polarizations remain far below conventional sources. Here, we introduce a photocathode-like scheme, applied to a gas of pre-polarized hydrogen and halogen atoms. A VUV and a visible laser pulse excite the halogen atoms to create a two-component ionization medium, consisting of low-threshold excited halogen atoms and high-threshold polarized hydrogen. Particle-in-cell simulations show witness beams with tens of pC charge retaining up to 97% of the initial polarization, rivaling state-of-the-art conventional sources.

physics.plasm-ph↗

arXiv2026

$λ$PIC: A callback-centric particle-in-cell framework

We present $λ$PIC, a Python-based electromagnetic particle-in-cell framework built around a callback-centric architecture. Existing PIC codes typically tie high performance to static, pre-compiled timestep loops, hindering implementation of custom physics, diagnostics, or output logic. $λ$PIC breaks this coupling by exposing every stage of the loop as a named stage (hook), permitting attaching arbitrary Python functions that operate on the full simulation state, enabling custom algorithms and in-situ analysis without modifying the core algorithms. Under this flexible framework, performance-critical kernels are written in C extensions and Numba, fields and particles are stored in NumPy arrays, and MPI parallelism is paired with graph partitioning to support dynamic load balancing and non-rectangular domains. Although $λ$PIC is designed as general-purpose, it has special focus on intense laser-plasma interactions. Future work will extend the framework to GPU acceleration and additional physics modules including implicit solvers and nuclear physics.

physics.comp-ph↗

arXiv2026

Radiation Reaction effects on Coherent Emission in Relativistic Magnetized Shocks

Relativistic magnetized shocks are natural sources of coherent radiation, representing a promising framework for fast radio bursts (FRBs). This study explores how the radiation reaction (RR) effect, triggered by high-energy photon emissions during shock radiation, significantly alters particle dynamics and coherent radiation properties. Using kinetic particle simulations, we demonstrate that RR severely suppresses electron energies from shock acceleration, resulting in multiple coherent gyration cycles at the shock front. It amplifies the intensity of coherent radiation and boosts energy efficiency by several fold, as compared to the single gyration cycle in the standard model of relativistic magnetized shocks. We further find that the coherent radiation spectrum from RR-mediated shocks is characterized by upshift peak frequency, broaden bandwidth, and narrow spectral peak. These RR-induced radiation changes may be related with several observed FRB phenomena, including the statistically positive correlation between luminosity and bandwidth in repeating and one-off FRBs, the narrow spectra seen in some FRB events, and the bimodal energy distribution reported in FRB 20121102A.

astro-ph.HE↗

arXiv2026

Vacuum-Triggered Instability in Paired Superradiance

Paired superradiance (PSR) is a macro-coherent two-photon process capable of very large gain, making it promising for detecting ultra-weak signals induced by neutrinos or dark matter. A major goal has been to increase the system volume $V$ and density $n$, since the signal intensity scales as $(nV)^2$. We recast finite PSR as a parametric amplifier driven by the electromagnetic vacuum. The usual zero-field semiclassical initial condition is replaced by vacuum inputs fixed by the quantum two-point function. Combining this formulation with Maxwell--Bloch evolution and finite-length stability analysis, we find that PSR produces an irreducible vacuum background that can develop into macroscopic bursts once the gain-length product exceeds $ΓL=π/2$ for a sufficient coherence time. These results, together with a closed-form formula for estimating the vacuum-seeded photon yield, establish a previously overlooked constraint for high-gain PSR, with direct implications for proposed neutrino and dark-matter studies.

physics.optics↗

arXiv2026

Radiative depolarization of high-energy electron beams in wakefield accelerators

The preservation of witness beam polarization in wakefield accelerators will be crucial for future collider applications. While extensive theoretical studies on the injection and initial acceleration of polarized electrons exist, a study concerning higher-energy regimes has been neglected thus far. Besides the spin precession usually considered in wakefield-related research, radiative effects could become increasingly relevant at higher energies as the witness electrons perform betatron oscillations during which they will emit photons. In the present study, we use particle-in-cell simulations extended with Monte-Carlo routines to study the influence of radiative spin-flips on beam polarization. We find that at high energies, the importance of radiative effects on beam polarization mainly comes down to the alignment of the witness beam with respect to the wakefield.

physics.plasm-ph↗

arXiv2026

Efficient Generation of Neutrons Based on Ultrashort Laser-driven Direct Acceleration in Microwire-Array Targets

We report on an experimental demonstration of efficient neutron generation based on direct laser acceleration in microwire-array targets irradiated by ultrashort (tens of femtoseconds) laser pulses. The optimal array period was identified, at which the maximum proton energy and the number of protons with energies exceeding $1~\mathrm{MeV}$ were significantly increased. Using a $1~\mathrm{PW}$, $\sim25~\mathrm{fs}$ laser at a moderate intensity of $\sim10^{20}~\mathrm{W/cm^2}$, a high neutron yield of up to $(8.33\pm0.84)\times10^{6}~\mathrm{n/sr/J}$ was detected from the LiD converter via $^7\mathrm{Li}(p,n)$ and $\mathrm{D}(p,n+p)$ nuclear reactions. Self-consistent integrated simulations reproduced the experimental results and predicted that with a Be converter, a forward pulsed neutron source with an unprecedented yield per joule of $3.67\times10^{7}~\mathrm{n/sr/J}$ can be obtained under identical laser conditions. This type of neutron source is favorable for applications that require a high repetition rate utilizing compact and economical laser systems.

physics.plasm-ph↗

arXiv2026

Pinching injection in wakefields for spin-polarized electron beams

Pinching of the driver beam in plasma wakefield acceleration is generally considered an unwanted effect that needs to be mitigated. Here, we propose that this effect can be utilized for the injection of spin-polarized electron beams from hydrogen halide targets into wakefields. Particle-in-cell simulations show that the electron spin is preserved on a level of 50% for a wide range of parameters due to the injection geometry. The presented injection scheme provides a possible pathway to alleviate some of the restrictions associated with pre-polarized hydrogen halide targets.

physics.plasm-ph↗

arXiv2026

Enhanced electron injection for efficient proton acceleration and neutron production in femtosecond laser-driven nano-structured targets

Micro- or nano-structured targets are advantageous in enhancing and manipulating laser-proton acceleration, due to the increased absorption of laser energy and onset of direct laser acceleration for high-energy electrons. Here, we experimentally demonstrate that nano-wire-array printed on a flat substrate is an efficient nano-injector of relativistic electrons that leads to a significant boost of laser-driven proton acceleration and neutron production beyond normal geometry. By employing an ultra-intense (2*1021 W/cm2) femtosecond laser pulse to irradiate nano-wire-array targets, protons with cut-off energies of 62.8 MeV are generated, and notably, the energy conversion efficiency from laser to protons reaches up to 9% - 3.5 times higher than that of flat foils. After bombarding a beryllium converter, 1.1*1010 neutrons are produced. Full 3D particle-in-cell simulations have reproduced experimental results and reveal interference mechanisms between the nano-wires and substrate, leading to continuous pumping of electrons from the substrate and standing-wave enhanced re-injection from the wire tip. This efficient injection finally results in the large sheath field and thus high yield of energetic protons and neutrons. Dependence on the wire length and scaling with laser amplitude are further discussed. These results suggest that 3D-printed structures are promising in developing compact laser-driven high-flux proton and neutron sources for numerous applications.

physics.plasm-ph↗

arXiv2025

Plasma acceleration of polarized particle beams

Spin-polarized particle beams are of interest for applications like deep-inelastic scattering, e.g. to gain further understanding of the proton's nuclear structure. With the advent of high-intensity laser facilities, laser-plasma-based accelerators offer a promising alternative to standard radiofrequency-based accelerators, as they can shorten the required acceleration length significantly. However, in the scope of spin-polarized particles, they bring unique challenges. This paper reviews the developments in the field of spin-polarized particles, focusing on the interaction of laser pulses and high-energy particle beams with plasma. The relevant scaling laws for spin-dependent effects in laser-plasma interaction, as well as acceleration schemes for polarized leptons, ions, and gamma quanta, are discussed.

physics.plasm-ph↗

arXiv2025

Collimated QED Cascades with Curved Plasma Mirror

Converting light into matter has been a longstanding goal in physics, particularly the creation of electron-positron pairs through quantum electrodynamic (QED) processes. While current approaches using multiple colliding laser pulses can achieve this conversion, they struggle to produce well-collimated particle beams - a crucial requirement for practical applications. Here we demonstrate that a single ultra-intense laser pulse, when reflected from a curved plasma mirror, can generate highly collimated electron-positron pairs with unprecedented efficiency. By focusing the laser to field strengths exceeding $a_0 > 2000$, our method triggers QED cascades that produce tightly focused particle beams, distinctly different from the diffuse plasmas created by conventional multi-laser setups. The technique works even at relatively modest laser powers of 13PW, making it immediately testable at existing facilities. This breakthrough opens new possibilities for studying fundamental QED processes and generating controlled matter-antimatter plasmas.

physics.plasm-ph↗

arXiv2025

Production of Iodine Isotopes via Ultra-intense Laser Driven Photonuclear Reactions

The investigation and production of proton-rich iodine isotopes predominantly rely on conventional accelerator-based methods, typically requiring prolonged irradiation periods to measure or achieve quantifiable yields for isotopic isolation. Bremsstrahlung radiation sources generated by high-power laser-plasma-accelerated electron beams with ultrahigh charge (tens of nanocoulombs) bombarding high-Z targets demonstrate extraordinary photon flux characteristics. An electron beam with a total charge of approximately 47.7 nC (E$_e$ $\gt$ 10.4 MeV) was generated in our experiment by focusing a ultra-intense laser pulse onto a deuterium gas jet. Laser-driven bremsstrahlung was employed to induce $^{127}I$$(γ,xn)$ ($x$ = 1,3,4,6-8), and the product yields and the corresponding flux-weighted average cross sections are reported. Our results demonstrate production of medical isotopes, with average yields of $^{124}$I and $^{123}$I at approximately $9.83\pm0.45\times10^{5}$/shot and $2.81\pm0.11\times10^{5}$/shot, respectively. This method, utilizing high-power lasers to generate bremsstrahlung radiation, shows significant potential for medical applications and opens new avenues for studying photonuclear processes in astrophysical contexts.

nucl-ex↗

arXiv2025

Zeptosecond Gamma-Ray Pulses Generation via FEL-Driven Microbunching and Laser-Compton Scattering

We introduce a novel and reliable approach to generate zeptosecond(10^{-21} s,zs), high-energy photon pulse bursts by synergistically exploiting the inherent characteristics of Free-Electron Lasers (FELs) and laser-Compton scattering. The feasibility of this scheme is validated through comprehensive numerical simulations. In a representative simulation, a 4 GeV electron beam, undergoing the FEL process, emits radiation at 0.7 nm and develops a microbunched structure. These microbunches subsequently interact with a 2 ps, 9 micrometers laser pulse in a head-on Compton scattering configuration. Our simulation results demonstrate that under conditions of well-established electron beam microbunching, the proposed method successfully yields high-brightness gamma-photon pulse bursts with durations approaching 800 zeptoseconds and exhibiting exceptional signal-to-noise ratios, consistent with theoretical expectations. This technique opens up avenues for exploring ultrafast nuclear dynamics and provides unprecedented perspectives for delving into the Quantum Zeno and Anti-Zeno effects.

physics.acc-ph↗

arXiv2025

Super light-by-light scattering in vacuum induced by intense vortex lasers

Collision of ultra-intense optical laser and X-ray free electron laser (XFEL) pulses is a promising approach to detecting nonlinear vacuum polarization (VP), a long-standing prediction of quantum electrodynamics remaining to be tested. Identifying the signals induced by polarized vacuum relies on purifying the X-ray polarization and poses significant challenges due to strongly reduced signal and low signal-to-noise ratio (SNR). Here we propose an approach that allows one to directly detect VP signals without the need for an X-ray polarizer. We identify a new VP effect in collision of an X-ray probe with an intense laser in a vortex mode, which we call the super light-by-light scattering (super-LBL), through which signal photons are kicked out of the X-ray background with large tangential momentum. Super-LBL originates from the gradient force of the vortical vacuum current in azimuthal direction and induces momentum exchange beyond the transverse momentum of laser-photon. This effect efficiently sets the scattered signal photons apart from the X-ray background, producing observable signals with both the strength and SNR more than two orders of magnitude higher than those from the known VP effects. This finding paves the way for single-shot detection of nonlinear VP phenomena with current ultra-intense laser and XFEL technologies.

physics.optics↗

arXiv2025

Self-seeded photon acceleration by electron beam-driven transition radiation

Photon acceleration (PA) driven by ultra-relativistic electron beams offers a promising approach to generating high-power, high-frequency coherent radiation sources. While current methods typically rely on external optical laser pulses injected into beam-driven plasma wakefields, they face significant challenges in synchronization and alignment between electron accelerators and laser systems. We propose utilizing transition radiation (TR) generated by the drive electron bunch transversing the vacuum-gas interface as the seed photons of PA. Using a 1 GeV electron bunch, we demonstrate acceleration of TR from 4.4 μm to 184 nm in 1.6 mm of two-stage uniform plasma, achieving more than a 20-fold frequency boost. Further frequency increases can be achieved with optimized setups. This scheme addresses the synchronization and alignment issues present in previous approaches, providing a practical path toward beam-driven photon acceleration.

physics.plasm-ph↗

arXiv2025

Superkick Effect in Vortex Particle Scattering

Vortex states of photons or electrons are a novel and promising experimental tool across atomic, nuclear, and particle physics. Various experimental schemes to generate high-energy vortex particles have been proposed. However, diagnosing the characteristics of vortex states at high energies remains a significant challenge, as traditional low-energy detection schemes become impractical for high-energy vortex particles due to their extremely short de Broglie wavelength. We recently proposed a novel experimental detection scheme based on a mechanism called "superkick" that is free from many drawbacks of the traditional methods and can reveal the vortex phase characteristics. In this paper, we present a complete theoretical framework for calculating the superkick effect in elastic electron scattering and systematically investigate the impact of various factors on its visibility. In particular, we argue that the vortex phase can be identified either by detecting the two scattered electrons in coincidence or by analyzing the characteristic azimuthal asymmetry in individual final particles.

hep-ph↗